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If coral didn't exist, would jellyfish not exist either? (Or vice versa)

If coral didn't exist, would jellyfish not exist either? (Or vice versa)


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Is the evolution of corals, sea anenomes and jellyfish intrinsically linked to the point where if say corals did not evolve, neither would jellyfish? Or vice versa.


I found this article with phylogenetic trees of Cnidaria answering your question. You should note that phylogenetic tress are statistical models based on sequencing. They may change depending on the methods used, the organismed sampled and the genes used for comparison I translated the groups you mentioned to the following biological names: Corals - Hexocorallia and Octocorallia Sea anenomes - Actinaria (Hexocorallia) Jellyfish - Medusozoa (Not the same levels)

Judging by Figure 3 (don't know if I'm allowed to post the figure to this site) And my limited knowledge in the subjet they each group could've evolve seperatley with a higher linkage between jellyfish & corals(octocorallia) than to sea anenomas. Sea anenomas and corals(hexocorallia) are very closly linked and sea anenomas appear at the first junction of the tree which means that if sea anenomas did not exists neither the rest of the group.


Comparison of 15 dinoflagellate genomes reveals extensive sequence and structural divergence in family Symbiodiniaceae and genus Symbiodinium

Dinoflagellates in the family Symbiodiniaceae are important photosynthetic symbionts in cnidarians (such as corals) and other coral reef organisms. Breakdown of the coral-dinoflagellate symbiosis due to environmental stress (i.e. coral bleaching) can lead to coral death and the potential collapse of reef ecosystems. However, evolution of Symbiodiniaceae genomes, and its implications for the coral, is little understood. Genome sequences of Symbiodiniaceae remain scarce due in part to their large genome sizes (1–5 Gbp) and idiosyncratic genome features.

Results

Here, we present de novo genome assemblies of seven members of the genus Symbiodinium, of which two are free-living, one is an opportunistic symbiont, and the remainder are mutualistic symbionts. Integrating other available data, we compare 15 dinoflagellate genomes revealing high sequence and structural divergence. Divergence among some Symbiodinium isolates is comparable to that among distinct genera of Symbiodiniaceae. We also recovered hundreds of gene families specific to each lineage, many of which encode unknown functions. An in-depth comparison between the genomes of the symbiotic Symbiodinium tridacnidorum (isolated from a coral) and the free-living Symbiodinium natans reveals a greater prevalence of transposable elements, genetic duplication, structural rearrangements, and pseudogenisation in the symbiotic species.

Conclusions

Our results underscore the potential impact of lifestyle on lineage-specific gene-function innovation, genome divergence, and the diversification of Symbiodinium and Symbiodiniaceae. The divergent features we report, and their putative causes, may also apply to other microbial eukaryotes that have undergone symbiotic phases in their evolutionary history.


As it happens, photosynthetic animals are not an example of something evolution hasn't stumbled upon. There are photosynthetic animals. Some of these, like the golden jellyfish, involve symbiosis with algae contained within the animal's body, but in contrast to this the oriental hornet converts sunlight directly into electrical energy using a pigment called xanthopterin, an entirely different approach to plants using chlorophyll. The pea aphid produces carotinoids, which animals were previously thought to be unable to make, requiring them to eat plants containing them instead. The aphid appears to be able to use the carotinoids it manufactures in order to produce ATP (Adenosine Triphosphate), which animals use for energy transfer.

Not all of the claims are undisputed: for the various species of green sea slug it is not yet clear whether the chloroplasts that they incorporate into their body provide them with sugar for energy, lipids for cell building, or nothing (just stored as camouflage colouring and something to digest later).

Humans also use sunlight to drive chemical reactions, although not as a source of stored energy. Humans can produce vitamin D when their skin is exposed to sunlight.


Methods

OMS Culture on Small Islands in the Coral Triangle: Case History of a Kuda Laut Demonstration Project

A demonstration project to culture H. barbouri as a sustainable livelihood in a land-based system was established on the small Spermonde Island of Pulau Badi (Fig.  1 ). Several of the authors developed the business model for the project and have been involved from inception to the present, allowing a rare opportunity for a case history.

The profit-and-loss business model for a production unit was calculated for 2014 based on the three units in production, the allowable quota, and price paid by exporter ex producer. Establishment costs were calculated assuming a 10-year lifespan of the main assets of tanks, solar panels, and batteries. Energy was calculated separately because it can change greatly if the island is completely electrified. Operational energy costs include purchase of power from the grid (when operating) and running a generator when solar power is low.

Based on the demonstration project, we generalized the process of establishing OMS culture as a livelihood option in the Spermondes and the Coral Triangle into three consecutive stages: (1) culture development and early adoption, (2) scale-up to franchise, and (3) large-scale adoption including risk management of the supply chain integrity and product quality. We then summarized the important aspects of successful culture in a Strengths, Weaknesses, Opportunities, and Threats analysis (‘SWOT’, Valentin 2001). Strengths were identified as advantages in competition, knowledge, human, and financial assets. Weaknesses were assessed as disadvantages including vulnerabilities in human and financial resources, infrastructure, and markets. Opportunities focused on the global market and potential offshoot livelihoods. Threats included competition, quality control, and environmental factors.

Indonesia OMS Exporters Interested in Cultured Kuda Laut

The kuda laut culturers sell directly to exporters. Exporters are critical links in the supply chain of OMS, and the OMS culture enterprise depends on them for transferring and air-freighting animals and export documentation, yet there is limited information on the OMS trade or culture from their perspective (Reksodihardjo-Lilley and Lilley 2007). We met with owners and/or executives of three of the largest, most experienced marine ornamental species exporter businesses in Indonesia (two on Bali, one in Jakarta) in March 2013 for a free-form discussion with each independently and a tour of their facilities. We specifically selected these exporters as opposed to a random sample because each was considered a ‘model’ exporter for the kuda laut project. Based on their high professionalism and experience, each had been approached initially about their interest in obtaining the licenses to sell the kuda laut product. One then obtained the licenses to sell seahorses from the project the others remained interested in doing so. All had been in business for 㸥 years and two generations, and belonged to the Indonesian Coral, Shell, and Ornamental Fish Association (AKKII, Asosiasi Koral, Kerang dan Ikan Hias Indonesia). One exporter previously also had an import business in southern California, a major destination for OMS exports (see “Results” section). These exporters are 𠆎nlightened’ sensu Reksodihardjo-Lilley and Lilley (2007) in that they provide training for their suppliers and have holding facilities that buffer offsets in supply and demand, allowing suppliers a more continuous income. The discussions were conducted in English and Bahasa Indonesia, and lasted until exporters decided that they had nothing more to impart (minimum 2 h each).

Indonesia’s OMS and Live Seahorse Trade

Seahorse and OMS culture must be considered both in the local Spermondes context as well as the international OMS trade originating in Indonesia. We thus gathered data on OMS exported from Indonesia to the United States, which is the largest importer of Indo-Pacific OMS, the majority of which enter through California (Balboa 2003 Wabnitz et al. 2003 Tissot et al. 2010). We obtained data on OMS imported from Indonesia into the ports of San Francisco and Los Angeles, California, USA, through a Freedom of Information request to the US Fish and Wildlife Service (USFWS)’s Law Enforcement Management Information System (LEMIS) for 2009, the most recent year for which data were considered complete by the agency. To supplement LEMIS records, we also observed a USFWS inspection at San Francisco International Airport (SFO) of a typical OMS shipment from Indonesia and obtained the invoice (exporter and importer information redacted). To our knowledge, the analysis is the most recent one for this major sector of the global OMS trade. For example, Rhyne et al. (2012b) reported quantities of ornamental marine fish importations into the entire United States in 2005 but not by country. Our data provide the first update of quantities of Indonesian OMS in the trade since Wabnitz et al. (2003), which reported fewer ornamental marine fishes imported globally from Indonesia between 1997 and 2002 than for California alone in 2009 (see “Results” section).

We also searched the CITES Trade Database (http://www.unep-wcmc-apps.org/citestrade United Nations Environmental Programme World Conservation Monitoring Centre, Cambridge, United Kingdom. Accessed 1 April 2014) to identify all import and export records for the genus Hippocampus from 2004 to 2012, which covers the first year of implementation for the species (starting in May) and the most recent year for which data are available. Only records designated with the importer term ‘Live’ were included in the analysis. Data were further parsed by combining the importer source codes 𠆌’ (bred in captivity as defined by CITES) and 𠆏’ (born in captivity to wild-caught parents as F1 or subsequent generations that do not otherwise fulfill definitions of 𠆋red in captivity’) compared to ‘W’ (taken from the wild).

OMS Culture: The Spermondes Food Fish Contrast

Culturing OMS cannot be evaluated fully without understanding the importance of food fishes and small-scale marine fishing integral to life in southwest Sulawesi. The Spermondes form the largest coral reef fishery in Indonesia, and fish is a major food source (Pet-Soede and Erdmann 1998 Budan Pusat Statistik, http://www.bps.go.id, accessed 10 April 2014). The fishery supplies both people in Makassar, the major city in southwest Sulawesi and where the catch is largely sold, and Spermondes islanders, who buy their daily fish back from Makassar as a consequence of the patron (‘middleman’)-client structure of the fishing industry (Ferse et al. 2012a). Makassar bills itself as a tourist destination for seafood, primarily fish. We sampled fishes in the Paotere fish market near Makassar, which is the largest of the two other fish markets in the region, for the quantity, diversity, and value of food fishes and numbers of people employed as vendors, to contrast with OMS culture. After a preliminary assessment visit to the market in 2012, we sampled the fishes being sold by randomly selected marine fish vendors on one day each in March (17 vendors) and September (25 vendors) in 2013 and March (25 vendors) 2014. We counted the total number of marine vendors at the market, photographed the fishes of each selected vendor, counted the number of individuals or estimated number if sold in baskets or piles, and asked vendors the price and where the fish were caught. Allen et al. (2003), White et al. (2013), Froese and Pauly (2013), and references therein were used for identification. We excluded tilapia and milkfish because they probably came from aquaculture.


Reafference and the origin of the self in early nervous system evolution

Discussions of the function of early nervous systems usually focus on a causal flow from sensors to effectors, by which an animal coordinates its actions with exogenous changes in its environment. We propose, instead, that much early sensing was reafferent it was responsive to the consequences of the animal's own actions. We distinguish two general categories of reafference—translocational and deformational—and use these to survey the distribution of several often-neglected forms of sensing, including gravity sensing, flow sensing and proprioception. We discuss sensing of these kinds in sponges, ctenophores, placozoans, cnidarians and bilaterians. Reafference is ubiquitous, as ongoing action, especially whole-body motility, will almost inevitably influence the senses. Corollary discharge—a pathway or circuit by which an animal tracks its own actions and their reafferent consequences—is not a necessary feature of reafferent sensing but a later-evolving mechanism. We also argue for the importance of reafferent sensing to the evolution of the body-self, a form of organization that enables an animal to sense and act as a single unit.

This article is part of the theme issue ‘Basal cognition: multicellularity, neurons and the cognitive lens’.

1. Introduction

Work on early nervous system evolution is generally shaped by the assumption that the main function of a nervous system is to control behaviour [1,2]. This task includes both adjusting action to the circumstances with the aid of the senses, and also the internal coordination of behaviour itself—shaping the micro-acts of parts of the body into the macro-acts of the whole [3–5]. Here, we look specifically at the side of neural evolution that involves behaviour and its relation to sensing we offer a reconceptualization of this aspect of neural evolution. The early functions of nervous systems probably also included the control of physiological processes and ontogeny [5], but these aspects are not considered here.

It has often been natural to explore this topic by considering ancient forms of sensing—chemotaxis, phototaxis, various forms of touch—and locating them in a causal flow in which external conditions are sensed and lead to a behavioural response. A tradition of work on more neurally complex animals, including arthropods and vertebrates, has argued for a different view of these relationships between sensing and action, one that makes central the concept of reafference: the effects of action on what is sensed [6] (see box 1 for a glossary of terms). Extending and redirecting these ideas, we develop the concept of reafference through the general principle that self-initiated action evokes sensory change, and then apply these ideas to early nervous system evolution. We show how reafference manifests itself in a number of senses—gravisensing, flow sensing, sensing associated with stretch—in non-bilaterian animals and simpler bilaterians. Through these examples, we also illustrate how the body's layout and form and its sensory systems have coevolved to use reafferent sensing. Reafference thus provides a unifying concept for neural and body-plan evolution. These considerations also shed new light on the origin of a ‘self’ in animal evolution, which we formalize in the concept of the body-self.

Box 1. Glossary of terms

Reafference: any effect on an organism's sensory mechanisms that is due to the organism's own actions

Reafference principle: self-initiated action evokes sensory effects that are correlated with these actions and, therefore, can be predicted and used

Exafference: any effect on an organism's sensory mechanisms that is due to external conditions or events

Corollary discharge: an internal pathway by which an animal tracks its own actions and their predicted reafferent consequences

Statocyst: specialized sensory cells or organs that track the motion of some part affected by gravity as the animal changes orientation

Proprioception: sensing of deformations, stresses and other mechanical changes within the body

Tensegrity: a design principle that is followed to build structures from rods under compression with attached cables imposing the compression

Deformational v. translocational reafference: reafference relating to body deformations as contrasted with reafference involving movement in relation to a medium or field

Body-self: a form of organization including motility, reafferent sensing and morphology enabling the organism to act as a single unit

Ctenophores: also called comb jellies, are gelatinous marine invertebrates that represent one of the earliest branching metazoan groups

Placozoa: disc-shaped millimetre-sized marine animals that glide upon surfaces by cilia

Choanocyte chamber: internal cavity in the aquiferous system of sponges with choanocytes that act as pumping and filtering units

Lateral line: a canal system with sensory ciliated cells that allows aquatic animals to detect fluid motion relative to the body

2. The reafference principle

The concept of reafference was introduced by von Holst & Mittelstaedt ([6] see also [7]) as part of a rival to a prevailing view of neural activity based on reflex arcs, with their simple flow from sensory stimulus to response. Von Holst and Mittelstaedt [6] argued for ‘a complete reversal of the usual way of looking at the system’, one that starts with action and inquires into the consequences of those actions on the senses—those consequences are reafference. Part of this reversal was a model in which animals continually establish and maintain states of ‘equilibrium’ by filtering their raw sensory input with ‘efference copies’ that register their own actions animals then refer the ‘residual’ of what is sensed to higher control centres as input that is indicative of externally caused events, or exafference.

This focus on efference copy and Sperry's [8] related notion of a corollary discharge tend to cast reafference as a disturbance of perception—and hence a problem—for which specific neural circuitry has evolved to compensate [9,10]. Here, we employ reafference in a more general way, one that stresses the importance of self-induced action as a central ingredient for perception. One way of casting this idea is in terms of a control loop where behaviour acts as a device that controls perceptual input [11–13]. A variety of related ideas are proposed in embodied approaches to cognition where action is held central to perception [14,15] and the role of the body is stressed in creating and shaping reafferent relations [16,17]. The way in which forward motion produces an optic flow across the visual field [18] is another example of a wider usage of reafference.

Here, we offer a view of reafference that goes beyond its original restricted use, but differs also from many of the broader theoretical claims that others have made for it. We do not hold that, in the light of reafference, perception itself becomes a form of action [15], or, conversely, that the function of action is to control perception [12] or to make it as predictable as possible [19]. From a biological point of view, action has many roles other than this. We do not use reafference to assimilate perception to action, or vice versa, though we do seek to reconceptualize their relationship.

Our discussion is guided, first, by what we will call the reafference principle: that self-initiated action evokes sensory effects that are correlated with these actions and, therefore, can be predicted and used. We understand reafference itself as any effect on an organism's sensory mechanisms that is due to the animal's own actions. A single sensory mechanism may on different occasions respond to reafferent or exafferent events reafference is a feature of sensory episodes, not mechanisms themselves. The paradigm examples involve motion of the body, but even a sessile animal can act with reafferent consequences, as when a filter-feeding animal generates a feeding current by motile cilia.

Second, reafference provides an opportunity, a resource, that can be exploited by animals. Many organisms use motion to elicit stimuli from the environment that would not otherwise arise. A bacterial example would be the way in which Escherichia coli and other bacteria use motility to assess the presence of a chemical gradient [20,21], while Gibson's ecological account of perception [18] articulated this idea in detail for animal vision. Self-initiated motion provides a stream of clues about environmental configurations. Reafference is not restricted to external motion but also applies to self-induced changes in body postures and feedback on imposed force as in active touch [22].

Third, given that self-initiated activities tend to have predictable consequences, reafference constitutes feedback concerning such predictions [13]. In this way, reafference provides a means by which organisms can evaluate these predictions and modify the activity involved. This need not involve a nervous system. For example, in sponges, sensory cilia keep track of the flow produced within the body and can signal when this flow ceases [23]. In animals with nervous systems, a corollary discharge is a more sophisticated mechanism that compensates for predicted sensory changes by registering the particular action underway at a time. With Crapse & Sommer [9], we use ‘corollary discharge’ rather than ‘efference copy’ to refer to this broad category.

Fourth, we differentiate between two forms of reafference, those relating to body deformations and those without shape changes but involving translocation or other movement (e.g. rotation) in relation to a medium or field (water, air, visual environment, magnetic or gravitational field). During deformational reafference, changes in the shape of the body lead to sensing, such as during proprioception. During translocational reafference, self-initiated motions induce an interaction with the environment with consequences for sensing (e.g. various flows). The impact of movement on statocysts and vestibular changes also belong in this category. The two categories are not mutually exclusive, and come together, for example, during active touch.

Most of the senses will be affected by the animal's own actions, and will hence give rise both to reafferent and to exafferent sensory episodes as seen below in the case of gravisensing, a sensory event may be due to self-caused motion or the action of waves. ‘Reafferent’ and ‘exafferent’ as defined here apply to episodes, classified according to their causes, rather than to mechanisms. However, we can also envisage a purely exafferent sensory mechanism—one that never produces reafferent episodes—such as an ambient light-sensing mechanism in a sessile organism, used to tune circadian metabolism. In that case, a stimulus guides an adaptive response, but the response has no effect on subsequent sensory events of that kind.

Here, we use the idea of reafference to cast light on early neural evolution and early animal life. Rather than a setting where specific neural circuits are being added to an already active animal, the question is how lumps of cells—with specific cell characteristics—evolved into organisms with many different cell types, a highly differentiated morphology and physiological organization, and sophisticated capacities for action and perception (figure 1).

Figure 1. Schematic of a basic and an evolutionary more advanced form of reafference. The scheme on the left represents an early animal with deformational reafference with an internal reciprocal influence between effector and sensory events. The schematic on the right depicts a more evolved animal with specialized sensors and effectors and corollary discharge mechanism. Deformational reafference is the sensory effect of a physical contraction of the body. Corollary discharge refers to a neuronal signal to filter reafferent sensing during action. (Online version in colour.)

3. The body-self

Another aim of this paper is to introduce and use a concept which we call the body-self. The term ‘self’ has many senses, some that involve complex thought and conscious experience, and some that are intended to be less demanding. Damasio [24] introduced the idea of a proto-self, to refer to a collection of brain devices that represent and maintain various states of the body in a range suitable for survival. His proposal, and others [25], can be seen as attempts to describe simpler precursors of the conscious human self. However, views like these still assume fairly high levels of biological organization, including the existence of a complex brain. Our concept is intended to pick out a more basic kind of self, one arising earlier in evolution, but one that is not trivially equivalent to the concept of an organism or physical object.

An organism has, or embodies, a body-self if it has a particular form of organization. That form of organization includes motility (of the whole or parts) and sensing, where action and sensing are tied together through reafference. The body-self then encompasses the devices and their activities that enable reafferent coupling between the animal's own actions and sensing. The body-self can thus include sensors and effectors, their activity or actions, and also the form of the body influencing reafferent coupling. In this view, brains, if they are present, are not the sole locus or even the centre of this self, but a part of the body that is characterized by this self. The body-self enables the organism to sense and act as a single unit, and thus a self that separates itself from the rest of the world.

A body-self has a non-arbitrary differentiation from its environment (though with some vagueness of boundaries) it marks itself off as a unit by the organization of its action, sensing and physical form. A body-self, when present, becomes a platform for further evolutionary innovation, including new kinds of sensing that draw on the prior demarcation of self from environment.

We apply the concept of the body-self to multicellular animal bodies. Unicellular organisms also have a form of self-hood, but it is simpler. They are divided from the environment by a single membrane and their activity is coordinated within that boundary (e.g. by ionic currents or second messengers). In a multicellular context, self-hood has to be reestablished by the coordination of parts and through reafferent sensorimotor loops. We acknowledge that reafference can also be relevant to describe the behaviour of single-celled eukaryotes but we do not discuss unicellular examples here (for an extensive discussion of single-celled behaviour, see [26]).

In the next sections, we discuss some forms of sensing and action that have a close relationship to the evolutionary emergence of the body-self in animals. These ‘self-forming’ sensory capacities feature reafference of various kinds, and also have a plausible role in early animal evolution.

4. Reafferent sensing and body-to-environment translocation

This section begins discussion of a range of examples of reafferent sensing in animals, especially non-bilaterian animals, and some other cases with relevance to the early history of animals. Early animals had limited bodily resources and simple nervous systems, when these were present at all. Our argument is that a significant and widespread feature of early animal evolution was putting available resources to work in handling and using reafferent connections between sensing and acting. No extant animals, even simple ones, can be assumed to resemble ancestral forms, but by means of a survey of present-day animals, we hope to show that a range of sensory capacities that plausibly feature in early animal evolution are capacities in which reafference plays an important role. Animals were building their ability to accommodate and use reafference as they were evolving their ability to sense and act. We begin our survey with cases of translocational reafference, one of two categories distinguished above.

(a) Gravity sensing

Once an animal is actively moving in any three-dimensional medium, it will tend to reorient in relation to Earth's gravity vector. If orientation is important (e.g. during vertical migration in the water column), a need will arise to control it by sensing and responding to orientation. Insofar as orientational changes to the gravity vector are produced by active motion, their sensory effects are reafferent in our sense.

The ability to sense the orientation of one's own body relative to Earth's gravity vector is present in many animals. Such active gravity sensing coupled to effector systems can lead to reorientation movements, maintaining or restoring a desired body orientation (as opposed to passive gravi-orientation). Gravity sensing relies on specialized cells or organs called statocysts in many animals [27]. Statocysts have a cavity containing small concretions or statoliths. When the animal changes its orientation relative to the gravity field, the statoliths move in the cavity and stimulate mechanosensory cells lining the cavity. The signal for the statocyst is generated by the tilt of the body and can lead to a response (e.g. the animal ‘righting’ itself). Such tilt may come about by self-generated movements or external forces (e.g. water turbulence). When actively induced tilt has sensory consequences, this qualifies as reafference. Reafferent gravisensing then contrasts both with exafferent gravisensing (in response, for example, to turbulence or waves), and with passive gravi-orientation, where the body acts as a buoy, as a consequence of the distribution of mass in its physical layout. Given that self-initiated activity almost inevitably leads to changes in the orientation of the body, reafferent gravity sensing will be useful as a means to compensatory reorientation.

The widespread use of statocysts across non-bilaterian animals suggests that they may have evolved early in animal evolution. In cnidarian medusae, there are several statocysts at regular intervals at the base of the tentacles [28–30] (figure 2). Ctenophores have a single statocyst in their aboral sense organ [32]. The statolith in this organ is attached to four groups of ciliated cells [33], one in each quadrant of the animal. Upon a change in body posture, the statolith presses the cilia and changes their beating frequency. This change propagates to the locomotor ciliary comb plates to reorient the body. The sensory excitation is graded with the beating frequency of the cilia changing as a function of statolith load [34].

Figure 2. Statocysts in a jellyfish and the placozoan T. adhaerens. (a) Scanning electron micrograph of a jellyfish, seen from below, showing the tentacles, statocysts (marked by asterisks), manubrium and gonads. Image by Jürgen Berger. (b) Schematic of a jellyfish changing its orientation. The statocysts are positioned around the circumference of the umbrella, and hence can signal body tilt in all directions. (c) Schematic of a Trichoplax and its crystal cells. Arrows show the orientation of the cup-shaped nuclei. Image from Mayorova et al. [31]. (d) Schematic of a crystal cell in different orientations relative to the gravity vector. The aragonite crystal in the cell moves relative to the nucleus. This movement likely induces a signal in the cell. After Mayorova et al. [31]. (Online version in colour.)

In the placozoan Trichoplax adhaerens, an animal lacking true muscles or a nervous system, there are crystal cells at regular intervals at the perimeter of the animal, each containing a 1–3 µm diameter aragonite crystal (figure 2). Upon changes in body orientation relative to gravity, the crystal shifts downwards within the cell. Animals lacking crystal cells are unable to move against gravity on a tilted plane [31]. Statocysts are also present in several bilaterians, including molluscs [35–37] and some annelids [38,39]. In gastropods, the pattern of responding hair cells in the statocyst is thought to allow the animal to determine its spatial orientation with respect to gravity [40].

There are also other types of gravity sensors. In flies, for example, the Johnston's organ is the gravity-sensing organ and it detects movements of the antenna [41,42]. A further example is the system of cercal gravity receptors in crickets with club-shaped sensilla that work like pendulums [43–45].

In gravity sensing and gravity responses, the reafferent coupling between actions and senses can only work if certain conditions are met. (i) The gravisensors need to be organized such that they can differentially signal the tilt of the body along all its cardinal axes, (ii) the sensory signals need to be graded in proportion to the magnitude of a tilt [34,46], and (iii) the statocysts need to control effector organs (muscles or cilia) such that the animal can right itself (gravi-orientation) and move up or down (gravitaxis). In such cases, we can speak of a gravisensory module of the body-self, encompassing the devices and their activities that deal with gravity in an active manner through reafferent coupling. As gravisensory modules evolve, this will affect nervous system organization because the body form affects the placement of sensors which influences nervous anatomy.

Elemental gravisensory systems can serve as a platform for the evolution of more complex circuitry and behaviours. One possible elaboration is to evolve the ability to switch the sign of gravitaxis depending on multimodal input deriving from other exterosensors. Such multimodal regulation of statocysts occurs, for example, in the pond snail Lymnaea stagnalis where low oxygen concentration switches gravitaxis from positive to negative [46]. In ctenophores, mechanosensory stimuli induce a switch in the sign of gravitaxis [34]. Another elaboration is to differentiate between reorientation caused by self-movement and reorientation due to external perturbations. Such differentiation is not essential for gravireception to function, but it could allow more elaborate motor control and would require a form of corollary discharge. In more advanced cases, statocysts can be recruited to the control of quite complex behaviours. In the marine planktonic pteropod mollusc, Clione limacina, the statocysts are involved in generating a complex swimming trajectory during hunting [36]. In evolution, statocyst networks can be elaborated, receive input other than orientational cues and even evolve intrinsic dynamics to guide complex behaviour through their motor connections.

(b) Flow sensing

Just as active motion induces changes in relation to the Earth's gravitational field, in aquatic organisms, it also induces flow. Flow sensors, widespread in aquatic animals, generally consist of one or more mechanosensory cells which have a sensory cilium deflectable by flow [27]. The cilium can be surrounded by microvilli, forming a mechanosensory apparatus where deflections are transduced into cellular signals by mechanosensory ion channels.

Through the example of flow sensation, we will illustrate how filter feeders and active swimmers use reafferent flow sensing and how reafferent sensing facilitates detection of exafferent causes of sensory change. We also show how reafferent feedback depends on the size and shape of the body and discuss some physical principles such as buoyancy, Reynolds numbers and flow fields, and how these impinge on reafference and corollary discharge.

Sensing changes in water flow can be relevant for both swimming and sessile organisms. Sessile or planktonic filter-feeding animals including sponges, ascidians, anthozoans and many other animals can generate feeding currents by cilia or muscular appendages (e.g. copepods) [47]. If the animal can sense this self-generated flow, it is readily enabled to detect deformations in the flow field caused by clogging or approaching objects such as predators distorting the flow field.

In sponges, putative flow-sensory cells in the osculum may sense a reduction in feeding flow from the choanocyte chambers due to clogging, initiating contractions to expel waste [23] (figure 3). Sponges also have an active control over the volume of water they filter and this depends on external flow [51]. In the demosponge Tethya wilhelma, a putative flow-regulating reticular cell type, the reticuloapopylocyte, has been described. This cell is situated at the excurrent pore of the filtering choanocyte chambers and has a fenestrated morphology with openings of variable diameter [49]. How self-induced flow, environmental flow and flow sensing interact to regulate flow rates is unclear, but it is possible that sponges have the ability to integrate information about the state of their canal system and environmental flows.

Figure 3. Flow-sensory systems in sponges and an annelid larva. (a) Schematic of the freshwater demosponge Ephydatia muelleri, after Leys & Meech [48]. Inset shows a slice of the internal wall of the osculum containing putative flow-sensory cells with 9 + 0 sensory cilia. (b) Schematic of a choanocyte chamber in T. wilhelma, after Hammel & Nickel [49]. (c) Scanning electron microscopy image of a reticuloapopylocyte in T. wilhelma from Hammel & Nickel [49]. (d) Scanning electron microscopy image of a 3-day-old P. dumerilii larva. (e) Flow field around a tethered P. dumerilii larva, beating with its locomotor cilia. Flow rates are very low at the stagnation point indicated by the white arrow. Red dots mark the position of the flow-sensory MS1 and MS2 cells. The flow was visualized by fluorescent microbeads. Image from Bezares-Calderón et al. [50]. (f) Morphology of two flow-sensory MS neurons in the 3-day-old P. dumerilii larva as reconstructed by serial electron microscopy [50]. (Online version in colour.)

Self-propelled ciliated larvae of metazoans can orient in flow fields [52] and can have flow-sensory cells. In larvae of the annelid Platynereis dumerilii, flow sensors (MS cells) are positioned at the most anterior tip of the head [50] (figure 3). In the flow field around the anterior tip of Platynereis, there is a stagnation point, where the local velocity of the fluid is zero. Such stagnation points are a general feature of the flow fields around self-propelled microswimmers (e.g. [53,54]). In Platynereis larvae, some of the MS cells are located at this stagnation point. This suggests that these cells will not be exposed to self-induced flow and may respond to external shear flow more efficiently. The filtering-out of reafferent stimulation, in a way akin to corollary discharge, is in this case achieved by the precise placement of sensors in a position defined by the hydrodynamics of the self-propelled body.

The shape and even the buoyancy of the body of small planktonic organisms can have various and non-intuitive hydrodynamic effects on the flow fields around a swimming body, the swimming trajectories and body orientation [55]. Larvae of the sand dollar, an echinoderm, are transported upwards or downwards in vertical flows depending on larval stage and morphology [56]. Detailed flow-field measurements around a swimming Volvox carteri—a colonial green alga—revealed that flows are dominated by a component due to gravity and the negative buoyancy of the colony [54]. Similar detailed measurements have not been carried out for planktonic animals, but many metazoan larvae are in the size range of Volvox (R ∼ 200 µm). If a planktonic organism has flow-sensory systems, these various hydrodynamic effects could thus dictate the optimal positioning of those sensors. This is one of many ways in which the physics of the body could feedback onto nervous system evolution.

A more advanced flow-sensing system is the lateral line in fish, tadpoles, lampreys [57] and possibly amphioxus [58]. During swimming, the lateral line experiences reafferent signals and the magnitude of these signals is tuned by modulatory efferent neurons. In tethered fish during fictive swimming, the spontaneous spiking rate of the lateral line afferent neurons decreases, in correlation with motoneuron activity [59].

The reafferent signal in swimming organisms also depends on the size of the body and size-related hydrodynamic effects. At the scale of ciliary microswimmers including animal larvae and other small plankton, viscous forces dominate over inertial forces (low Reynolds numbers). By contrast, larger animals like fish operate at higher Reynolds numbers where inertia is more important. A fish after a swim bout will glide in the water, without motor activity. During gliding, reafferent signals can still activate the lateral line. The corollary discharge can persist during the glide phase [59], suppressing reafferent signals even without a motor action. This is a good example to illustrate that in a corollary discharge system, it is not sufficient to have a simple ‘subtraction’ of the motor command itself, but the system needs to predict the consequences of the motor action, given the nature of the body and environmental setting. In the fish example, inertia, given the body and its milieu, is one physical aspect that will influence how an action plays out.

Similar principles could be applied to the evolution of visual systems and optic flow sensing. The first eyes in animal evolution likely already relied on reafferent sensing. The simplest eyes are non-visual phototactic eyespots that rely on the helical rotation of the swimming body to scan the light field [60–62]. For organisms with more complex visual eyes, self-induced optical flow provides an important mechanism to orient themselves with respect to the environment. The changes in visual texture, signalled by the light falling on an array of photoreceptors, provide the animal with information about objects, pathways to traverse and imminent collisions [18,63–65]. In a way that is comparable to the forward point of stasis in Platynereis larvae, the direction of movement is simply signalled by the point in the visual array from which all other points diverge. In addition, in many cases, corollary discharge mechanisms are present. In the fly compound eye, for example, voluntary turns are associated with an efference copy that suppresses the response to the turn in the visual cells [66]. A similar suppression of movement signal happens during saccades in the primate eye [67].

5. Reafferent sensing and body deformation

We now address forms of reafferent sensing that keep track of changes in the body itself. Although the term ‘reafference’ has been most often used for effects of action on exterosensors, the distinction between self-caused and other-caused sensory events (reafference and exafference) is also available in the case of interoception. Sensing body deformation involves a wide array of proprioceptors, for which we use Lissmann's long-standing definition: ‘Sense organs capable of registering continuous deformation (changes in length) and stress (tensions, decompressions) in the body, which can arise from the animal's own movements or may be due to its weight or other external mechanical forces' (cited by Mill [68, p. xvi]). In this context, the physical characteristics of the animal body are central, as well as the various ways in which it can be actively deformed by its own activity. Here, we will first describe the notion of tensegrity structures as a way to integrate a wide array of processes and forms of organization that are involved in body deformation and reafference, including biochemical, biomechanical, physiological and cytological processes, as well as the overall organization of animal body shape. This will provide the background to discuss reafferent sensing in touch and epithelial stretch, and in muscle proprioception.

(a) Animal bodies as tensegrity structures

At heart, the animal body is a soft deformable structure, built up from epithelia folded and expanded during development. In contrast with plants and fungi, animal cells have no rigid cell wall and the combined cells lack rigidity that has only secondarily, and not in all cases, been reinforced with specialized structures, including sponge spicules and a variety of internal and external skeletons made up from various materials (shell, bone, chitin, etc.). These skeletons notwithstanding, the animal organization remains one that can be dynamically deformed on short notice by contractions of muscle cells, or precursors thereof, that can both deform and stabilize body shape [69,70] and be used to initiate bodily movements.

The animal body shape is a dynamic feature even when it is outwardly unchanging. A useful concept here is tensegrity or tensional integrity. Tensegrity is a general design principle that is followed to build structures from rods under compression with attached cables imposing the compression. The integrity of the structure arises from a combination of rigid and elastic components combined under tension. This form of organization also applies to the animal body. Here, a skeleton constitutes the rigid parts that oppose compression, while muscle and tendons (mostly) constitute the flexible component that, by means of tensile forces, binds the skeleton together [22].

For early animal evolution, three differences with the original tensegrity concept are relevant. First, the tensile components can change length by muscle contraction and relaxation, making the tensegrity structure capable of dynamic and reversible changes. Second, early cases did not have hard skeletons, so the opposing force for a muscle system derives instead from more diffuse hydrostatic skeletons that, like water-filled balloons, provide a flexible but incompressible mass [71]. Third, the dynamically changing mechanical forces involved in these animal tensegrity structures themselves constitute signals that travel across large parts of the body—like using a connecting rope to ring a faraway bell—and influence biochemical processes at the cellular level. For example, mechanical connections between extracellular fibres and the cytoskeletons of individual cells modify the latter [72–74] and stretch-activated ion channels change their bioelectrical properties under mechanical stress [75,76]. At larger scales of aggregation, proprioceptive sensors add to the neural modulation of such changes [68].

Dynamic tensegrity structures constitute an active and very flexible motile organization, which requires suitable (and complex) coordinative control to maintain body shape [74,77] and organize behaviour [3,5,22] as also can be witnessed in work on soft robotics [78–80].

The sensitivity of cellular processes to the dynamically changing pattern of mechanical forces across the tensegrity structure makes reafference an intrinsic ingredient of this organization. Self-generated forces imposed on the structure will influence proprioceptive sensors both at a cellular and at a multicellular scale [81]. The importance of force-dependent molecular switches that react to developmental tissue deformations has been well established [73–77]. Here, we address behavioural examples involving body deformation where reafferent sensing plays various roles.

(b) Proprioception

All animals are able to actively change their body shape through actomyosin-mediated contractions. Ctenophores, cnidarians and bilaterians use muscles for shape changes. In placozoans, ultra-fast epithelial contractility underlies shape changes [82]. Some sponges also undergo coordinated contractions, involving various contractile cell types in their canal system and outer surface [83].

Cellular sensors responsive to deformation or contraction-induced stresses might evolve as an intrinsic ingredient of such dynamic shape changes. When the contractile effectors and connected tissues are stretched or compressed, this could induce mechanosensory currents, providing the basis for reafferent signals (figure 4). Compared to body-to-environment translocation, the presence and the nature of such proprioceptive reafference are more difficult to establish. We first give an overview of bilaterian cases of proprioception, before discussing the possibility of its presence in non-bilaterian animals and when in animal evolution it might have appeared.

Figure 4. Stretch sensation and proprioreception. (a) Schematic of a hypothetical early animal with orthogonal muscle fibres forming a tensegrity structure. (b) Cellular-level stretch sensation by mechanosensory channels. Upon deformation or contraction, stretch-sensitive channels (e.g. Piezo) can open, leading to an internal reafferent feedback. (c) Specialized neuronal proprioreceptors in the fly larva. The ddaE and ddaD neurons have sensory dendrites that deform during larval crawling. ddaE is more active during forward locomotion, while ddaD activates during backward locomotion. Sketch after He et al. [84]. (d) Sketch of a putative cnidarian proprioceptor in the cerianthid C. americanus, after Bezares-Calderón et al. and Peteya [27,85]. The sensory dendrite including the cilium and the stereovilli are embedded in a muscle cell. Muscle contraction may provide proprioceptive feedback. (Online version in colour.)

Proprioceptors sensing muscle stretch are widespread and well studied in bilaterians. In crawling Drosophila larvae, different proprioceptors sense body wall deformations either during muscle contractions or extension [86]. There are also different subtypes of proprioceptive neurons that either are more active during forward or during backward locomotion [84] (figure 4). Proprioception in the fly is dependent on the pan-metazoan transmembrane channel Tmc [87] that may sense the membrane curvature in proprioceptor dendrites [84]. The proprioceptors provide feedback about body position by synaptic connections to premotor neurons [88].

Adult Drosophila incorporate a broad variety of mechanoreceptors, many of which act as proprioceptors [89]. For example, chordotonal organs are found on exoskeletal joints and between joints within limb and body segments [90]. Campaniform sensilla are oval domes on the exoskeleton with a thin cuticle covering a sensory dendrite. They sense mechanical stresses that bend the exoskeleton. Stretch-sensitive receptors also occur in connective tissue or linked to muscle. The mechanosensitive ion channels TRP-N [91] and Piezo-like channels [92] are involved in proprioception. A detailed study of leg proprioceptors revealed subgroups encoding leg position, movement direction and vibration frequency [93]. Crabs have similar systems sensing muscle stretch and leg position [94].

Proprioception is also well understood in the nematode Caenorhabditis elegans [95]. One of the stretch-sensitive proprioceptive neurons, DVA, expresses a transient receptor potential (TRP) channel TRP-4 (a homologue of TRP-N/NompC) and regulates locomotion behaviour. Trp-4 mutant worms show abnormal body bending and posture [96]. SMDD is another proprioceptive neuron that is activated during head steering locomotion to modulate the curvature of forward motion. Two TRP channels, trp-1 and trp-2, are necessary for head proprioception [97]. In addition, the body wall muscles themselves are also mechanosensitive [98]. Movement not only affects neuronal activity through proprioception in C. elegans, but also through corollary discharge. Head motor commands during head movements are encoded by the RIA interneurons that are reciprocally connected to head motoneurons. Movements are encoded on a subcellular scale in RIA neurons through compartmentalized calcium dynamics [99,100].

In vertebrates, proprioceptors sensing stretch are found in muscle spindles and Golgi tendon organs [101]. Mechanosensitivity in these sensory cells is dependent on the ion channels Piezo2 and Tentonin3 (TTN3) [102–104]. The proprioceptive cells feed back onto motor neurons in the spinal cord [101]. Defects in proprioception can lead to abnormal gait and a loss of coordination of body movements [105]. In fish, mechanosensory feedback during movement is provided by spinal cord sensory neurons (Rohon–Beard neurons and Kolmer–Agduhr cells). The mechanosensitivity of the Kolmer–Agduhr cells depends on the polycystin channel Pkd2l1 [106,107].

The evidence supporting the presence of muscle or stretch proprioceptors in non-bilaterians is at best fragmentary. Cnidarians and ctenophores can have relatively complex muscular behaviours [32,108], and some form of proprioception may be present to ensure coordinated behaviour. An electron microscopic study by Peteya [85] reported putative proprioceptive cells in the cerianthid cnidarian Ceriantheopsis americanus (figure 4). These cells have a ciliated sensory apparatus that runs parallel to the long axis of the animal's body. The sensory cells have both afferent and efferent synapses suggesting a feedback system. The efferent synapses derive from the motoneurons innervating the body wall and may modulate the sensory cell's sensitivity during muscle contractions [85]. Similar cells with their cilia closely associated with epidermal circular muscles are found in the tentacles of the cubozoan jellyfish Carybdea marsupialis [109].

Placozoans undergo substantial and rapid changes in body shape by fast epithelial contractions [82]. It remains unclear whether these shape changes induce any stretch-dependent monitoring of body shape.

Some sponges can also actively change their body shape by contraction and extension [51,110–112]. A well-known case is the ‘sneeze’ of the freshwater sponge E. muelleri. This sponge uses peristaltic-like contractions to expel clumps of waste material from its water canal system, suggesting ‘that control over a hydrostatic skeleton evolved prior to the origin of nerves and true muscle’ [83, p. 3736 113]. The fine tuning of the canal diameter may be linked to flow sensation at the excurrent canals, as discussed above. Flow sensation of the contractile state of the canal system may be considered as an indirect form of proprioceptive feedback.

A further interesting example of putative proprioceptive systems comes from studies of sponge and coral larval settlement. Whalan et al. observed that sponge larvae preferentially settle in holes with a size that matches the size of the larva. This selective settlement guided by surface microtopography may be achieved by mechanosensation [114].

The ancestral presence of various mechanosensory ion channels in animals indicates that some form of mechanosensing was present at the origin of the animals. At least initially, this may only have been a form of cellular or tissue-level stretch sensing and without specialized mechanosensory cells. One class of ancient ion channels present in animals and many protists is the Piezo mechanosensory channels [115]. These channels are required for mechanically induced currents in cells and could serve as cell-autonomous stretch sensors. Piezo has also been identified in Trichoplax and may induce currents upon shape changes [116].

The mechanosensory TRP-N family (first described as NompC in Drosophila [117]) is also ancient and is present in cnidarians, ctenophores and placozoans but not poriferans [87,118]. TRP-N mediates many mechanosensory functions such as the control of body movement and perception of touch in nematodes [119] and in flies [91]. Besides TRP-N, up to six TRP channel families date back to the origin of animals or before [87].

Given the ubiquity of mechanotransduction channels, it may be that mechanosensation represents one of the oldest sensory processes that evolved in animals, directly connected to contraction-based motility [76].

6. Reafference and the evolution of animal bodies and nervous systems

Along with new species and new traits, evolution occasionally produces new kinds of living units—new kinds of selves. The nature of such a new form can include the layout and materials of the body, capacities for acting and sensing, and systems of coordination and control, such as nervous systems and others. The animal body-self is one such form of organization, resulting from evolutionary change in all these areas. The existence of a body-self is a matter of degree. In its paradigm cases, a body-self is unified by neural control, reafferent sensing and a suitable morphology, all of which facilitate action at a multicellular level. Non-neural animals can have a partial body-self of this kind, as can physically connected colonial forms where self-hood is distributed between a collective and its constituent zooids. During evolution, the mechanisms enabling unified sensing and action, with accompanying morphologies, became more elaborate, giving rise to body-selves of different varieties. We sketch here some possible pathways in early animal and neural evolution that relate to the body-self and draw on the ideas in earlier sections of this paper.

Unicellular organisms are compact enough to behave as units in quite complex ways without large-scale coordination of parts. The origin of animals produced larger units, composed of many cells, that were often invested in a lifestyle that puts a premium on coordinated action on their new spatial scale. Cell–cell signalling, eventually including nervous systems, became the basis of this coordination.

A plausible starting point for the animal body-self can be found in collections of cells that came to act as dynamically changing soft-bodied tensegrity structures. The shape changes of such structures depend on a self-imposed and self-maintained interplay of compressive and tensile forces that, in turn, can modify cellular signalling in various ways. An animal body is, therefore, not merely a collection of cells, but an integrated unit tied together by mechanical forces. When appropriately coordinated, the collective becomes a unit capable of doing mechanical work—changing its shape and moving—and also becomes a platform for various sensory devices.

In almost any unit that can both sense and act, alongside the theoretically familiar causal paths from sensing to action, there will be pathways from action to the senses. Reafference is an almost inevitable consequence of the combination of acting and sensing. Reafference brings with it both ambiguities in sensory input and opportunities to actively probe environments. It is a feature of sensing even before the evolution of nervous systems. The evolution of sensory systems will have been affected by the near-inevitability of reafference from early stages. This phenomenon will be particularly marked in the case of the sometimes neglected forms of sensing we have discussed in this paper: gravisensing, flow sensing, stretch sensing and proprioception. Sensitivity to the consequences of action of this kind may also establish, through its shaping of sensitivity on a multicellular scale, paths to new forms of exterosensing. These paths eventually yield forms of sensing in which reafference and exafference combine tightly together, in actively moving animals, including lateral line sensing in fish and active vision as discussed by Gibson [63].

Non-neural animals are restricted to limited coordination and agency. Their bodies, while materially unified, are not tied together as selves in the same way that a neuralian animal is. Despite this, their sensing will include reafference to some degree. Nervous systems then bring with them new possibilities for integration. As well as the familiar ways that a nervous system integrates control, the expansion of agency that nervous systems make possible can shape the form of the body itself. Work in Hydra has revealed several non-overlapping neural networks responsible for particular behaviours [120]. In most cases, these networks are each spread throughout the entire body, but remain distinct from each other they do not form a single connected ‘nerve net’. Though the networks are distinct, their interaction within a soft body may generate not only behavioural sequences but also aspects of the body's form. Dupre & Yuste suggest that the Hydra morphology may result from the ‘push–pull’ action of two opposed ectodermal networks, constituting a soft-bodied tensegrity organization.

Even unconnected neural networks within a single behaving body will be linked by reafference. Proprioception may also be present. However, a point can be made here about the different roles, within cnidarian lifestyles, of polyp and medusa forms. The polyp body plan is thought to be the ancestral form in cnidarian evolution, with the medusa appearing later. A medusa actively swimming in the water column engages in more organized, integrated behaviours. A polyp, in contrast, might get by with less integrated control, as seen in Hydra. Sensory systems are also more elaborate in the medusa form, with gravisensing (discussed above) and, in some cases, significant visual ability [121]. A related evolutionary pathway—perhaps overlapping at early stages—may exist in ctenophores. Here, too, a plausible scenario has a sessile polyp-like form as ancestral, perhaps existing before a branching that produced cnidarians and ctenophores, still with polyp-like bodies [122,123]. From there, both lineages evolved a more active medusa-like form. Ctenophores use cilia rather than body contraction for swimming, though muscle is employed in steering. In both cases, the more active, motile form brings with it a more integrated variant of the body-self. Sophisticated reafferent sensory systems such as statocysts also seem to have evolved independently in the medusoid form in ctenophores and cnidarians. The large degree of parallel evolution between ctenophores and cnidarians plus bilaterians—as evidenced by molecular comparisons [124]—may partly be due to their independent conquest of the pelagic zone.

The evolution of the bilaterian body plan brings with it a further expansion of behavioural repertoire, with new possibilities of mobility and manipulation. Common across a range of animals whose genealogies coalesce only in the protostome-deuterostome common ancestor (nematodes, arthropods, vertebrates and others), nervous system activity includes global or brain-wide dynamic patterns that are associated with particular actions [125]. In some cases, the expansive spread of these patterns makes problematic any simple distinction between ‘sensory’ and ‘motor’ areas in an animal. These are action-directed patterns that can also be modulated by impinging external events.

Across a similarly wide range of bilaterians, reafference is addressed and mobilized with corollary discharge mechanisms. Reafference becomes not just a standing fact about the relations between sensing and acting, but something whose presence shapes neural architecture, which now includes circuitry that modulates the processing of sensory signals according to what the animal is currently doing.

At present, corollary discharge mechanisms of this kind are not known in non-bilaterian animals. This has two possible explanations. First, it may be that the utility of these mechanisms is tied to the breadth of a behavioural repertoire. When an action is produced continually or routinely (a swimming motion, perhaps), its reafferent consequences can be handled implicitly, without a neural circuit indicating which action is being produced at a particular time. Alternatively, such mechanisms may be present, though not yet observed perhaps even routinely produced motions require registration of ongoing actions as part of regulatory feedback. If so, we hypothesized that if corollary discharge mechanisms are present in cnidarians, their likely location is in association with advanced sensory mechanisms in medusoid forms, such as statocysts and cubozoan eyes [121].

The evolution of corollary discharge mechanisms, in response either to an expansion of behavioural repertoire or the demands of fine control, has further consequences. An animal with this organization handles sensory events in a way that includes an active neuronal marking of the distinction between self and other. Its organization embodies a self in a richer sense. Organisms without a neuronal corollary discharge may already have the ability to distinguish self and other through intrinsic differences in sensory events (e.g. between active contraction or being squeezed). We mentioned Damasio's notion of the ‘proto-self’ as a candidate for a kind of implicit self-concept that is prior to a fully fledged, reflective human sense of self. As noted, Damasio's proto-self is dependent on extensive neural organization and internal sensing. Before the proto-self arose, animals were not just objects with various sensory and effective adaptations collected together. They were integrated in a way that gave them an earlier kind of self-hood. We introduced the concept of the body-self to describe the devices and activities that enable reafferent coupling between the animal's own actions and sensing, together with the body's own layout, all of which enable the organism to sense and act as a single unit. As we have argued throughout the paper, to get going as an animal, you need a body-self, with its utilization of reafference, pretty early. The body-self then provided a platform for further stages in animal evolution, including the evolution of complex nervous systems, and more elaborate and explicit forms of the self.

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All authors contributed to conceptualization and writing—all authors agreed to the submitted version of the manuscript.


Principle 4 &ndash Rights and responsibilities

Democracy is often thought of as majority rule which is true to the extent that 50% plus 1 of the votes will get people elected and pass legislation, but it is also an ideology holding that all people are equal, that by the fact of being human they are born with rights which are not dependent upon obligations and duties. Rights exist because of those obligations and duties. Liberalism maintains that the individual is the foundation of society. All of its insinuations are abstract and do not resemble the true nature of humans as revealed through history. By a person fulfilling obligations and performing duties to the State, each individual is entitled correspondingly to rights. Rights are not inalienable nor granted by appeal to metaphysics. They result only from one's interaction with the State.


Chapter 2 Vulnerability of Marine Turtles to Climate Change

Marine turtles are generally viewed as vulnerable to climate change because of the role that temperature plays in the sex determination of embryos, their long life history, long age-to-maturity and their highly migratory nature. Extant species of marine turtles probably arose during the mid–late Jurassic period (180–150 Mya) so have survived past shifts in climate, including glacial periods and warm events and therefore have some capacity for adaptation. The present-day rates of increase of atmospheric greenhouse gas concentrations, and associated temperature changes, are very rapid the capacity of marine turtles to adapt to this rapid change may be compromised by their relatively long generation times. We consider the evidence and likely consequences of present-day trends of climate change on marine turtles. Impacts are likely to be complex and may be positive as well as negative. For example, rising sea levels and increased storm intensity will negatively impact turtle nesting beaches however, extreme storms can also lead to coastal accretion. Alteration of wind patterns and ocean currents will have implications for juveniles and adults in the open ocean. Warming temperatures are likely to impact directly all turtle life stages, such as the sex determination of embryos in the nest and growth rates. Warming of 2 °C could potentially result in a large shift in sex ratios towards females at many rookeries, although some populations may be resilient to warming if female biases remain within levels where population success is not impaired. Indirectly, climate change is likely to impact turtles through changes in food availability. The highly migratory nature of turtles and their ability to move considerable distances in short periods of time should increase their resilience to climate change. However, any such resilience of marine turtles to climate change is likely to be severely compromised by other anthropogenic influences. Development of coastlines may threaten nesting beaches and reproductive success, and pollution and eutrophication is threatening important coastal foraging habitats for turtles worldwide. Exploitation and bycatch in other fisheries has seriously reduced marine turtle populations. The synergistic effects of other human-induced stressors may seriously reduce the capacity of some turtle populations to adapt to the current rates of climate change.

Conservation recommendations to increase the capacity of marine turtle populations to adapt to climate change include increasing population resilience, for example by the use of turtle exclusion devices in fisheries, protection of nesting beaches from the viewpoints of both conservation and coastal management, and increased international conservation efforts to protect turtles in regions where there is high unregulated or illegal fisheries (including turtle harvesting). Increasing research efforts on the critical knowledge gaps of processes influencing population numbers, such as identifying ocean foraging hotspots or the processes that underlie the initiation of nesting migrations and selection of breeding areas, will inform adaptive management in a changing climate.


The Case For Reality: Because Apparently Someone Needs to Make One

This morning, I read an article on consciousness and physics ("The Case Against Reality" in The Atlantic). The beginning of the article starts off with a broad statement: That our senses aren’t completely accurate that the world isn’t perfectly represented them.

It's a relative statement so it’s not worth disagreeing with. That is, given the scope of our space telescopes and quantum detectors -- yeah, we do a crappy job of perceiving. But, compared to the capabilities of a jellyfish or just total blindness, we do a great job at perceiving reality.

But then the article goes on to describe: (1) that external reality simply isn't there, (2) our science is flawed for assuming so and trying to measure it, (3) that the brain doesn’t exist, because it’s "a classical object" according to quantum mechanics, and, (4) that the whole universe is "conscious observers" all the way down.

"I’m emphasizing the larger lesson of quantum mechanics: Neurons, brains, space … these are just symbols we use, they’re not real. It’s not that there’s a classical brain that does some quantum magic. It’s that there’s no brain!"

I will dive into why quantum doesn't imply this, later in the article. If there is any "larger lessons" to be drawn from the sciences, it would be that relying on intuitive argumentation (the main tool of academic philosophy) has historically ended up being wrong. The larger lesson of psychological sciences actually shows that intuition is easily misled and completely biased by experience.

The professor's stance is based on the idea that perfect objectivity doesn't exist, and therefore, by extension, pure subjectivity is all that exists. He uses physics to back up this idea.

First, let's clarify the physics details.

The article says all observation, all science, all attempts at objectivity is belied by a major flaw: “Physics tells us that there are no public objects.”

Public objects is a made-up term, not a physics one if you're wondering implying that we all essentially live in our own private universe with our own private objects -- that is, you and I cannot perceive the same 'public' object. If you assume objects are 'public' -- that is, if you assume you and I can both perceive the same thing -- we will fail. He says that this dramatic personally-exclusive reality is implied by physics.

Classical physics describes 'public objects' all the time with great precision. You and I can both use our own telescopes, even be on different sides of the planet, observe the same comet, and use gravity equations to know where it will go next and when. We will observe the same thing, arrive at the same prediction.

The more modern physics of enormous objects ('theory of relativity') can successfully describe momentums, energies, velocities, and masses from any vantage point you pick in a system. Yes, counter to our initially-limited intuition, if one vantage point is travelling close to the speed of light, it will observe different masses, velocities, and even passages of time. But, all these vantage points within this system are consistent with each other.

In fact, using the theory, you can pick any vantage point ("observer"), and then proceed to describe the rest of the public objects.

"Snakes and trains, like the particles of physics, have no objective, observer-independent features."

Many physics-inspired word artists conflate our sense of self (consciousness, subjectivity, etc) with the use of the word "observer" in physics. Physics uses the word “observer” a lot. It uses the word in relativity theory as described above. In that case, it refers to from which vantage point you are looking at the rest of the system.

“Observer” is also used it in quantum physics. Specifically, the wave function collapse principle which predicts a particle's probable actions after its been "observed".

"Experiment after experiment has shown—defying common sense—that if we assume that the particles that make up ordinary objects have an objective, observer-independent existence, we get the wrong answers."

In this case, the principle he's attempting to refer to is that subatomic particles are probabilistic and we can’t determine ahead of time what they’ll do exactly. We use wave equations to describe the possibilities of what could happen and the probabilities associated with them. Once measured (usually by hitting these particles with a photon of light and seeing where it bounces), we can collapse the probabilities down to a narrower range of possibilities ('wave function collapse'). This measurement is sometimes referred to as an observation. Basically, these particles are "non-deterministic" or "indeterminate" between measurements.

At this very small scale, particles don’t have a perfectly determinable position and speed they take on a vibrational probabilistic quality that is only revealed or made less cloudy by colliding or becoming aggregate with a larger system. The larger system, whether it be a particle detector, a computer and a human scientist, is referred to as an observer. But, the vibrational and probabilistic path of a lone particle is unknown until it’s "observed" (that is, measured by a system).

Hopefully, its clear how quantum physicists are using those words.

Quantum Behavior Doesn't Imply that Our Subjectivity Is Super Important to the Universe

Nor does it imply, (and I get into this because this point gets implied a lot by "mind philosophers"), the system or measurement is required to include human eyeballs and a human brain. The particles don’t care whether someone is in the room to look at the data. Or whether that person is brain dead. Or whether another living species is looking at the screen. The word ‘observation’ does not imply an observer needing consciousness.

This might seem like an odd point, but this has been suggested by some since quantum behavior was discovered (1930's). "Observer" means when subatomic particle action is observable because it becomes aggregate with a larger system. Any larger system. But some people think that these words imply that "consciousness" pins down these particles, and minus that, the particle, and the entire universe, is libel to do anything.

The counter-joke to this, from physicists, is that would mean the universe was waiting around for billions of year for someone with a PhD to observe it, in order to manifest into a more determinate state.

Of course, we would tend to think our subjectivity is important. Hopefully, its clear how incredibly self-obsessed these philosophizing attempts are. Its like watching your friend on drugs proclaim his felt connected-ness to the moon because his visual system and empathy system are perturbed by drugs. And then insist to you that this feeling actually implies something about the moon rather than his brain.

Quantum Doesn't Mean That Everything is as Fuzzy as a Single Particle Is

I recently read the beginning of Max Tegmark’s book, describing a single calcium ion, particles small enough to be appreciably influenced by quantum action, rushing into a single neuron, theoretically causing a thought that in a parallel universe he wouldn’t have had. Yeah, if a single calcium ion could do that, that might be true. Except, it’s more like a million calcium ions. With another million waiting by if those didn’t rush into that single neuron. And the magnitude of a single firing of a single neuron on any of your thoughts being analogous (in terms of scope) of you forgetting to vote and that having any influence on the California primaries. He's trying to describe a system so sensitive and perilously on the edge, that a single "quantum" action gets biologically amplified all the way up to a macroscopic process.

We rush towards explanations that amplify incredibly tiny perturbations. Chaos theories. A single voice influencing social movements. A blinding insight or thought. Its a protective narrative to reinforce our focus on the tiny part we have control over. To associate motivating feelings of meaning with that narrative. But things happen in aggregate. You can, in fact, use mathematical models to demonstrate the robustness of the inertia of large systems to single, or even many, aberrant events.

Quantum behavior doesn't imply that all daily objects we clearly observe (and even manipulate), which are made up of these small particles, are now forever "un-determined" and that nothing is real. The reason we don't perceive the fuzziness of particles is because with any large number of objects (voters in elections, cells in human biology, wind currents in weather), seemingly chaotic individual behavior becomes pretty determinable in aggregate.

The "lessons" of quantum physics (such as the somewhat-indeterminate nature of particles) doesn't generalize to even a large set of particles joined together, much less, macroscopic objects. Even a single molecule (such as a large protein or DNA strand), an aggregate of thousands or more atoms, becomes visible and ceases to exhibit quirky quantum behavior of single particles.

Even with single particles, they aren't completely indeterminate. They just can't be completely pinned down with perfect accuracy. This isn't just because of measuring limitations its because these particles are literally buzzing around. All of science so far has observed this quantum behavior, only and precisely in the context of really small and individual particles, but not in large objects. Quantum physics doesn't imply the whole universe can't be pinned down at all.

Quantum and Free Will

This article didn't imply this point but I've seen this one also. Sometimes, errant metaphors are drawn between the probabilistic paths of particles and our perceived free will. The probabilistic nature of a particle having multiple path possibilities (which is what a wave function describes -- probability of it taking varying paths) and collapsing to one of these possible paths when measured should not be conflated with your mind’s ability to think of multiple futures and then (sometimes) having something similar to one of your previous thoughts, happen to you, as a perceived decision. The metaphor is possible, yes. But it doesn't go very far. It doesn't mean that free will is implied by quantum behavior.

It's just our anthropomorphic tendency to associate human-like qualities (a complex psychology with somewhat unpredictable behavior) to electrons. Its also our tendency to infer a causal link between two patterns that seem similar.

Just Use "Quantum" In Everything

The professor also describes failures in neuroscience progress is the failure to work in quantum rather than “Newtonian physics” when looking at neurons ("and yet my field says, 'We’ll stick with Newton, thank you. We’ll stay 300 years behind in our physics.'"). I've also heard this revelation from high and drunk scientists at parties before. That, somehow, the equations describing the fuzzy, probabilistic qualities of particles could somehow unlock all the other sciences (or predict the stock market, etc). That we just need to ram those equations onto the other sciences.

The action's of neuronal axon potentials, actions of atoms and molecules within a cell containing at least quadrillions (and more) atoms, the subtle electric fields given off by massive amounts of neural cells firing together, do not become even slightly more accurate with wavefunction descriptions.

It would be cool if one set of equations generalized to everything but these don't. As neither does Relativity Theory -- the equations describing the slight bending of space or warping of time that occurs with really huge objects (like our sun). We don't try to shove the equations of relativity into our neurosciences (or whatever else) either. They just don't work outside their context.

Again, the "lessons" of quantum physics doesn't just generalize to everything. We didn't find the Philosopher Stone when we examined particles. We just found out that at a really, tiny resolution, individual particles behave in such a vibrating and somewhat indeterminate manner (not infinitely indeterminate either), that they can hop around a bit, take on multiple fuzzy positions, even collide with themselves, and are just less tethered to space and time.

Nor does this imply that each one of us are (physically) living in our own exclusive universe. Obviously, from our mind's point of view, we each do each have our own exclusive biological reality connected to a personally exclusive brain -- but this doesn't extend to the world beyond or the entire universe.

The Philosopher's "Consciousness Field"

"I’m claiming that experiences are the real coin of the realm. The experiences of everyday life—my real feeling of a headache, my real taste of chocolate—that really is the ultimate nature of reality."

I recognize that people with a stated affiliation in cognitive neuroscience inherently contain self-centered tendencies (that is, obsessing about their own mind works) but the point of the field isn't to strive towards solipsism. The view of some "cognitive philosophers" is that consciousness is not just a vague term roughly summarizing complex phenomena from a helicopter view but, rather, a fundamental entity or field in the universe.

Perhaps, that last part slipped past you. Buckle in for this.

A literal entity or field (in case that wasn't emphasized enough). That, stay with me here, if you hack atoms down into electrons and protons, and then those into quarks, and then hacked those further, you would find "consciousness." Some kind of a fundamental consciousness entity/particle/field. This is a theory by some academic philosophers. Everything built on that "consciousness field", and that all of reality is tenuous, bending to pure subjectivity. Again, not how it just seems to us. But to use teenage vernacular, they mean everything is literally-literally consciousness. To use philosophical vernacular, you can see how this view would strike scientifically-striving individuals as probably the most solipsistic view one could have on the universe.

This concept of a "Consciousness Field" continually comes up, represented by academic philosophers keen on walling off a niche with obscuring language, and maintaining a cross-fire of grossly over-confident and data-less shots backed by self-obsessed and limited intuitive aim. This reenactment of academics scares off commentary from the scientific academics with loudness of the blanks they fire. Publicly, this phenomena is popularized by a large drug culture that is keen on proving meaning to their neural short-circuiting trips that feels so real, and spiritualists who reject old religion but still possess psychologies that find the universe to be not only simmering with meaning, but itself literally feeling meaning, an appealing reassurance.

Actual Consciousness

"Consciousness" is a term we use to roughly summarize complex behavior of other people. Usually it implies people are capable of responding in some way (e.g. an "unconscious" patient isn't responsive in any complex way other than the simpler spinal cord and brainstem reflex circuits). In locked-in syndrome, it means the person can't respond (direct any muscle movement including eyes and voice) but is still inputting information through their senses, comparing it against their memories, and updating their summaries of the world. They are conscious but we have a harder time telling because of general muscle paralysis.

The article refers to split brains and states that each half is conscious. But, then also, refers to whole brain, before it was split, being conscious. How is this possible?

Split brains are an interesting medical and neuroscientific example. You can show that each half of the brain processes information from its half of the body (and interprets that information with whatever abstraction centers are on that side -- language tends to be lateralized to one side), and is limited by the physical split. So, in that case, the side missing the language center can still perceive objects through the sensory nerves hooked up to that side,, but can't come up with the words for them.

This really points to the fragility of the concept of “consciousness” rather than proving you can split (or conjoin) “consciousness” infinitely. Consciousness refers to comparisons in input from whatever is in memory. Its a contrast of the environment (and senses of your body) filtered up into summary representations, that are constantly changing and are rich in informational detail. Awareness, feelings, and consciousness are explainable as physical deterministic processes.

"It suggests that I can take separate observers, put them together and create new observers, and keep doing this ad infinitum. It’s conscious agents all the way down."

No, if we hacked your brain down to bits, each one would not possess the same capacity of consciousness you have/feel now. In fact, if we stroked out small select parts of your brain, you would lose a lot.

Informational "Consciousness"

By the broadest and abstract-est of definitions, consciousness as an informational definition (past state + current inputs), can be applied to subatomic particles, the sun or anything. But it’s not experiencing the same spectrum of informational states, language, perception or anything else that you are experiencing, except in this extremely abstract sense that, it too, processes its current state against the context of its previous state. But again, not in any way remotely similar except by abstract metaphor. So that definition is poetic only, probably criminally confusing and almost completely unuseful.

And even this abstract definition that I've just described (as stripped down as it is to even work this generally) is more of a generalized information description that doesn't usefully relate to biological/medical consciousness that well. The various cognitive philosophers I've read, never even make a case this coherent for some kind of general information processing mechanism.

Even if you tried to push this information processing abstraction forward, particles don't possess complex memories from multiple points in time and containing thousands of features to compare against such as in a neural network or your brain. It also doesn't contain memories of how it was feeling (essentially summaries of your body's state) associated with those features or points in time. In fact, if we're drawing associative patterns here, much of the phenomena in quantum physics shows the opposite pattern. That is, the particle's past doesn't matter at all to how it will act next.

Again, any similarity the professor sees in brains and particle behavior, is a reflection of his own brain's biases in how it represents the world. Not in the world itself.

To extend it past that at all, is an anthropomorphic simulator in your head (evolved, useful, but limited) gone awry. These are the same circuits responsible for you cursing at your car or yelling at wind blasting you in the eyes. To simulate psychology in anything complicated in the world around you can be useful: It allows you to summarize and predict other people's (and animal's) actions --- useful in contexts with other people. But, again, easily overextended to other complex phenomena, where you're projecting psychologies and intent into the weather, laptops, or the universe.

Social "Consciousness"

The article also refers to a mathematical model of consciousness that say any group of interacting consciousness is essentially one consciousness.

Right, it could. As a social definition of consciousness. A team working together, a corporation, a bobsled team, could appear to be a single "consciousness" acting on its environment. But it depends on the resolution of your summaries (or "symbolic representations" in a model). On the other hand, an entire body of work (fictional dramas even) can be written on just two people, each sharing some secrets from each other, and having shared knowledge with each other, each with different histories to compare against. As a social definition, some consciousness is shared, but to the level that 'consciousness' (that is, memory, previous experiences, inputs) isn't shared is extremely relevant to us.

Evolution Of Our Mind

The obfuscation attempts are revealing when he uses physics to imply no reality exists, then jumps to evolution to prove it shaped us to aggressively filter out all reality (which apparently now exists).

"Evolution has shaped us with perceptions that allow us to survive. They guide adaptive behaviors. But part of that involves hiding from us the stuff we don’t need to know. And that’s pretty much all of reality, whatever reality might be."

The article elaborates on an evolutionary theorem that claims to prove evolution is driven by "fitness" over "reality perception":

"The mathematical physicist Chetan Prakash proved a theorem that I devised that says: According to evolution by natural selection, an organism that sees reality as it is will never be more fit than an organism of equal complexity that sees none of reality but is just tuned to fitness. Never."

Maybe, "reality-perceiving" (if that could even be captured as a stand-alone abstract definition. ) does take a backseat to another evolutionary driver, but is still really up there as a priority in evolution. Maybe reality-perceiving isn't identical to fitness but still overlaps with fitness. Maybe it overlaps almost completely with fitness. A lack of an absolute doesn't mean the complete opposite is true.

Also, there's a real issue with abstracting out fitness like this. You could try to put things like hair color or working metabolic enzymes on a spectrum somewhere between "mostly incidental" and "helped your fitness a lot". Your metabolic enzymes were required to survive and were probably aggressively selected for.

On the other hand, there are probably fitness contributions from minor aesthetic differences in hair color. Yes, hair color probably takes a huge backseat priority to your metabolic enzymes in terms of environmental survival. Yet, this doesn't prove that hair had no contribution at all to individual fitness (probably as a sexually competitive trait) or that the selection of good metabolism forced us to have the least sexy hair colors possible (which would be analogous to what he's claiming).

Fitness refers to all the properties that allow an agent to (1) thrive and persist against elements in an environment, (2) as a group against competing species, and, (3) if its not asexually-reproducing, to be selected for against other members of the same species. Perception of the environment with more accuracy and clarity (that is, more useful mental models) is part of this. But, so is skeletal frames, muscles, metabolic enzymes and other stuff.

In fact, the physical reality, ironically the thing that purportedly does not exist, shares influences in shaping evolutionary selection. So, yes, we don't evolve as ethereal, disembodied, conscious entities because the selection of our cognitive and mental faculties had to co-evolve with a bunch of physical stuff. This is precisely because the world is real, physical and not pure consciousness.

This isn't to say that, by evolutionary principle, organisms have to be driven only by 'survival against the elements' fitness. Evolution could do this only fractionally, and be mostly driven by something environmental like aesthetics (that is selected for, such as in dog-breeding), or model accuracy (such as in evolutionary-designed algorithms in a computer) or whatever the environment deems as fitness. It may be that in recent evolutionary history in humans, with our physical form mostly hashed out, clarity and perception got more emphasized by the environment and sexual selection.

Our Probably-Evolved Mental Bias

Yes, your mind's ability to interpret reality has a bias wired into it (and ability to bias) that is explainable by evolution. Again, this isn't about "quantum physics" telling us "public objects" aren't "available." Nor, it isn't about us actually living in some forty-two dimensional Gak-filled universe, our biology being able to sense that, but our minds not perceiving it because we cognitively filter it out because "snake avoidance" is quicker without it:

"But part of that involves hiding from us the stuff we don’t need to know. And that’s pretty much all of reality, whatever reality might be. If you had to spend all that time figuring it out, the tiger would eat you."

You do have a bias wired into your mind. It is probably evolutionary. Your brain does possess a resilient ability to maintain narrative summaries/explanations that seeks to ignore (and even become unaware of) what it can't control, and remain long-term statistically optimistic even when the immediate, local environment isn't promising.

Your brain can also filter inputs deftly, at many levels and without your awareness, to convince yourself these narratives are true. It may be that those individuals lacking this, in the evolutionary timescape, offed themselves or just sat down and died.

However, truth-wise, this cognitive bias means that you are, in essence, perceiving the genetic reality (that is, the extremely long-term reality) quite accurately even when the momentary reality all around you gives you only dismal evidence (or vice versa). Compared to the reality of a particular crappy day, your optimism (or pessimism) might seem inaccurate. But maybe, compared to the reality of the long-term, you may possess a genetically more wise viewpoint that is actually more true. In that case, you're wired for truth. Depends what the scope of the reality is that you're talking about.

This bias isn't anything to do with quantum probability equations. Its just a bias wired into your valuation and judgement algorithms in your brain. Algorithms that sometimes fail in some moments, but were hammered out with a billion years of reality immersion.

Models and Mathememagics

First, keep in mind, he can't state anything about the scope ("pretty much all of reality") from just a model.

Secondly, he also makes a conclusion from a model which selects for fitness, to conclude that fitness is more important than other features (ability to perceive reality). This is like judging dogs at a dog show purely by size, then commenting that its amazing that, according to a dog show that you're running, larger dogs always seem to be more aesthetically pleasing.

"The mathematical physicist Chetan Prakash proved a theorem that I devised that says: According to evolution by natural selection, an organism that sees reality as it is will never be more fit than an organism of equal complexity that sees none of reality but is just tuned to fitness. Never."

Yeah, any added specificity will limit "fitness", the general indicator of success, in a "fitness" model. If your model restricts any feature, only redheads, or tall people, or double-jointed thumbs -- then, yeah, it will be more limited overall. There's so many definitions and assumptions in this, it would be annoying to parse them all out.

The point is models are board games and you can design them however you wish. Just because the board game you designed happens to consistently bias the game for the first player over the second, doesn't generalize into some broad lesson about going first or second in life. And, it certainly doesn't "mathematically prove" anything.

The Problem with Philosophy From the Mind

The lesson from physics, if there is one, is that the very experiences we rely on, the ones feeding out intuition, are limited compared to the scope of light years or the smallness of sub-atomic particles.

We learn this, in fact, by probing reality with the least subjective approaches we can come up with. The take-away from all of this is to rely on sciences to continue to incrementally provide us with nuggets of reality. The lesson of human progress has shown that grand attempts at Holmesian inferences about the nature of all things, from a philosophical armchair, doesn't work.

That last statement is in reference to "cognitive" philosophers who pontificate on the "infiniteness" of "free will", or just claim, despite evidence, that the universe couldn't have arose from "physical nothing", or claim the universe is, itself, "consciousness." They rely on logic and words to make these conclusions, without realizing that word and logic actually have limits. Without realizing that our logic and words are completely based in limited experience and are actually being changed by our observations from science and new experiences.

Despite the progress of science, there are a slew of self-labeled "philosophers of the mind" who fall backwards into their own subjectivity, right after pointing to evidence of our successful progress to work around our subjectivity, and conclude that attempts at objectivity is pointless and that completely isolated subjectivity is all there could ever be in the universe.

"Here’s how I think about it. I can talk to you about my headache and believe that I am communicating effectively with you, because you’ve had your own headaches. The same thing is true as apples and the moon and the sun and the universe. Just like you have your own headache, you have your own moon."

Of course we have our own perceptions, interpretations, and preferences. It's important to note, though, he's not pointing how as biological creatures we tend to be obsessed with our subjectivity. That's true. It's super important to us. But, he (and other philosophers like him) claim that reality itself is just as fickle and varied and subjectivity-obsessed as our minds. He (and others) use physics to say that complete subjectivity is all there really is in the universe itself:

". the idea that objectivity results from the fact that you and I can measure the same object in the exact same situation and get the same results — it’s very clear from quantum mechanics that that idea has to go."

"Philosophy of the mind" continues to be a cognitively infantile view on the evidence of physics (and science in general). It's probably why I continue to be engaged by it. The field continues to serve as a concentrated demonstration of all our mind's tendencies and fallacies (despite being self-proclaimed experts in logic and fallacy). Cognitive tendencies and fallacies that are present everywhere in our world but they are particularly purified, refined and concentrated in their field. It's almost a human cognitive experiment in itself.

They generalize absolutist narratives about all of reality from one or two phenomena of physics, while being oblivious to the fact that these very actions [over-generalization of patterns creating idealized absolutes and trying to project them onto the world around us narratives with casual agents possessing empathy and personality self-protective and reinforcing explanations] are limited tendencies of the brain, not limitations of the universe itself.

Abstractions, Generalizations and Metaphors

"You could not form a true description of the innards of the computer if your entire view of reality was confined to the desktop. And yet the desktop is useful."

That's true. For the computer user, its an accurate-enough representation. For someone who needed to fix the hardware of the computer, they're going to need more or different representations.

Abstractions and representations may seem like an esoteric point to the reader. But if you have an image of yourself and an image of myself in Photoshop, these are symbolic representations of us. If you keep blasting them with filters long enough, they will eventually look similar. Perhaps even indistinguishable. You will get the shadows of two eyes, a shadow of a mouth. Those are just pictures though. Representations of two entirely different people.

Maybe you can say that's a "face."

You could really go crazy with Photoshop filters and do this with your face and a sunset. Eventually, you get two identical white blobs and they will appear the same.

Maybe you can say that's a "thing."

Symbols, words, cave paintings are just attempts (sometimes useful) to represent real things in abstraction (not just that one dog but all dogs, etc) by removing some detail. Its the same thing with models, math, equations and technical definitions.

Abstraction can be useful. But, it can also easily be so abstracted that you're just looking at two white pages that used to have colors and lines, saying "your face is basically the sun." Yeah, that's poetic but how is that even remotely useful? The universe and your brain both have "complicated structure", too. That really doesn't help much. Its just an association rather, than, a predictive pattern embedded in a specific context.

This is why you can't just drive all the way right off the idealized-absolutes-generalization cliff, even though your mind is driven to find broad pattern predictors (or one grand pattern predicting everything). That's what your mind does find associations. Sometimes, they are patterns. Sometimes they are predictively useful.

Sometimes you're shaking a stick at the sky and dancing in a circle hoping it will rain again. The field of physics and neuroscience have extremely reliable models for guessing what a object will do next or how strongly a group of neurons will fire next.

Within their respective contexts.

When you generalize or make metaphors, you need to stay slightly back in the context. In the details. Because the context is where the pattern becomes useful.

I hope you can see why extremely abstract representations of brains (to the point of losing any context or useful detail) and his representations of the universe, appearing identical or similar to each other, doesn't imply anything. Its just a useless exercise in abstraction, stripping out all relevant detail.

Really, whats going on is a borrowing of the most fragile concepts, to gain credibility and shroud in obscurity. Concepts like "consciousness," "observer" and "non-deterministic."

Purposely slamming around limited words like this well outside their context, borrowing the credibility of multiple fields while simultaneously discrediting them, doesn't contribute much in my opinion.

This particular example in The Atlantic takes this a step further than the usual consciousness-physics turdball by throwing a math spin on it to “prove” things (remember, math proofs can show that math is consistent with other math you can’t “prove” a principle of evolution, that's a misappropriation of the word "prove"), and then distracting the audience with the narrative that is evolutionary theory.

This article (and the theories of "cognitive philosophy") is really, a beautiful example of conflation. Conflation relies on misusing, stealing, and borrowing words. Words meant to represent a certain concept in a specific context. Fiat currency that is taken outside its borders and attempted to be redeemed.

The Chuck-E-Cheese tickets and Dave & Buster’s cards that are attempted to be redeemed at a third location altogether, include “observer” and “consciousness”. The key to this confusion is that few experts work at both of these establishments (physics, neuroscience).

Obscurantism has a lot of niche space to thrive in our modern era of knowledge. Poetic connections are not only possible, but in our brain's tendency. This should not discount the approaches we've taken to get this far:

"The idea that what we’re doing is measuring publicly accessible objects, the idea that objectivity results from the fact that you and I can measure the same object in the exact same situation and get the same results — it’s very clear from quantum mechanics that that idea has to go."

Essential part: "objectivity . that idea has to go."

Objectivity is a continuum. Of course, perfect objectivity isn't an achievable point. But our (increasing) ability to interpret reality more objectively lets us build skyscrapers and global cellphone networks. Something about reality, the way we interact with it, the way we and our systems interpret, is allowing us to manipulate it with increasing success. The very fields he references are testaments to that.

I hope you have a clearer summary of physics, consciousness, evolution, and models (or are at least motivated to find one) than what this bit of disreality has offered. Credit to The Atlantic, at least, for shining light even if not a disinfecting one, upon an ongoing epidemic that people sometimes tell me has long since been eradicated.


1. Introduction

Work on early nervous system evolution is generally shaped by the assumption that the main function of a nervous system is to control behaviour [1,2]. This task includes both adjusting action to the circumstances with the aid of the senses, and also the internal coordination of behaviour itself—shaping the micro-acts of parts of the body into the macro-acts of the whole [3𠄵]. Here, we look specifically at the side of neural evolution that involves behaviour and its relation to sensing we offer a reconceptualization of this aspect of neural evolution. The early functions of nervous systems probably also included the control of physiological processes and ontogeny [5], but these aspects are not considered here.

It has often been natural to explore this topic by considering ancient forms of sensing𠅌hemotaxis, phototaxis, various forms of touch𠅊nd locating them in a causal flow in which external conditions are sensed and lead to a behavioural response. A tradition of work on more neurally complex animals, including arthropods and vertebrates, has argued for a different view of these relationships between sensing and action, one that makes central the concept of reafference: the effects of action on what is sensed [6] (see box 1 for a glossary of terms). Extending and redirecting these ideas, we develop the concept of reafference through the general principle that self-initiated action evokes sensory change, and then apply these ideas to early nervous system evolution. We show how reafference manifests itself in a number of senses—gravisensing, flow sensing, sensing associated with stretch—in non-bilaterian animals and simpler bilaterians. Through these examples, we also illustrate how the body's layout and form and its sensory systems have coevolved to use reafferent sensing. Reafference thus provides a unifying concept for neural and body-plan evolution. These considerations also shed new light on the origin of a ‘self’ in animal evolution, which we formalize in the concept of the body-self.

Box 1.

Glossary of terms

Reafference: any effect on an organism's sensory mechanisms that is due to the organism's own actions

Reafference principle: self-initiated action evokes sensory effects that are correlated with these actions and, therefore, can be predicted and used

Exafference: any effect on an organism's sensory mechanisms that is due to external conditions or events

Corollary discharge: an internal pathway by which an animal tracks its own actions and their predicted reafferent consequences

Statocyst: specialized sensory cells or organs that track the motion of some part affected by gravity as the animal changes orientation

Proprioception: sensing of deformations, stresses and other mechanical changes within the body

Tensegrity: a design principle that is followed to build structures from rods under compression with attached cables imposing the compression

Deformational v. translocational reafference: reafference relating to body deformations as contrasted with reafference involving movement in relation to a medium or field

Body-self: a form of organization including motility, reafferent sensing and morphology enabling the organism to act as a single unit

Ctenophores: also called comb jellies, are gelatinous marine invertebrates that represent one of the earliest branching metazoan groups

Placozoa: disc-shaped millimetre-sized marine animals that glide upon surfaces by cilia

Choanocyte chamber: internal cavity in the aquiferous system of sponges with choanocytes that act as pumping and filtering units

Lateral line: a canal system with sensory ciliated cells that allows aquatic animals to detect fluid motion relative to the body


The importance of symbiotic relationships to all living organisms on the Earth cannot be understated. All across the globe, in every ecological community in the world, from those viewable with the naked eye to those only seen under the lens of the microscope, symbiotic relationships remain crucial to maintaining balance in nature's multiple processes.

Symbiotic relationships cross taxonomies and species and involve most all living creatures on the planet in some way or another. Symbiotic relationship help to provide people with food, populate the planet with trees and plants, and keep animal and plant populations in balance. Symbiotic relationships can help individual species to evolve or change and even thrive. Without symbiotic relationships, there would not be any coral reefs, trees might not proliferate as far and wide as they do, aided by the birds and insects that transport seeds afar, and even human beings might not have survived long enough to evolve into Homo sapiens – Earth's modern humans.


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