Should consciousness be a defining property of living organisms?

Should consciousness be a defining property of living organisms?

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High school students in India under the CBSE Board are taught that consciousness is a defining property of living organisms. This question lies under the topic of 'What defines living organisms?' Does that mean that if robots and other artificial intelligence have consciousness and can react to some external stimuli (just like plants), they are alive? Also, what about the patients in coma or those who are 'brain-dead', are they alive or dead?

Then, how do we define living in terms of science?

A possible answer in my opinion to the second question above could be that life begins at conception and an organism is considered alive till the point where it has no differences with the dead; i.e. a person who is 'brain-dead' would still be considered alive because he/she still isn't the same as a dead person.

So should consciousness be a defining property of living organisms?

Edit: Defining Consciousness-
In the NCERT textbook which is used to teach the CBSE high school students in India, consciousness is explained as the ability to sense the surroundings or environment and respond to the environmental stimuli which could be physical, chemical or biological.

For reference: NCERT Class 11 Biology Textbook~ Unit 1: Chapter 1, Page 5 (second paragraph) Link to book: 1

tl;dr this is an extremely unusual definition of "consciousness" (I'd be surprised if you can find it in any standard English dictionary). If you prefer, like Humpty Dumpty in Lewis Carroll's Through the Looking Glass, to define words (in this case "consciousness") in any way you want - i.e., as above ("ability to sense the surroundings or environment and respond to the environmental stimuli… "), then consciousness is indeed one of the defining characteristics of life.

This property is (arguably) necessary, but not sufficient, for life - things can be 'conscious' (respond to stimuli) but not be alive, but they can't be alive if they don't respond to stimuli.

This property is more typically called irritability. The Khan Academy article on "What is Life?" gives this property under the section "Response" (along with the the other properties "Organization", "Metabolism", "Homeostasis", "Growth", "Reproduction", "Evolution"). (You can also find it in lots of biology textbooks in this Google Books search.) The text you refer to uses similar criteria (growth, reproduction, metabolism, cellular organization, 'consciousness').

As Khan Academy also says, it's hard to be precise:

Living organisms have many different properties related to being alive, and it can be hard to decide on the exact set that best defines life

So, to answer your specific examples:

  • robots respond to stimuli (and, arguably, have organization and metabolisms), but they don't grow or reproduce. If they did, we might call them living organisms.
  • people who are brain-dead or in a coma still exhibit some degree of response to the environment/irritability. So do dormant seeds, spores, and other "resting stages" of organisms.

There are always edge cases; is a sterile person (or indeed one who can't reproduce because they're in a coma) "alive"? The Khan Academy web page uses a similar example, the case of mules (the infertile hybrid offspring of horses and donkeys), along with several other examples that illustrate some of the more difficult cases (dieocious/gonochoric organisms that are isolated from members of the other sex [can't reproduce, but still considered alive]; fire ["reproduces" but not organized or homeostatic]; crystals [not homeostatic, don't evolve]).

Characteristics of Living Organism: Growths, Reproduction and Metabolism | Biology

Living organisms have ability to grow, reproduce, to sense environment and provide a suitable response. Livings organism have attributes like metabolism, ability to self-replicate, self-organize, interact and emergence. All living organisms grow, increase in mass and increase in number of individuals having twin characteristics of growth.

A multicellular organism grows by division of cells. Growth by cell division occurs throughout their life span. In plants, this growth is seen only up to a certain age. In animals, however, cell division occurs in certain tissues to replace lost cells. Unicellular organisms also grow by cell division.

In most of the higher animals and plants, growth and reproduction are mutually exclusive events. A dead organism does not grow. Development is a sequential phenomenon. It is directed by genetic code. One stages after another which is irreversible process.

Growth is defined as increase in size and mass during the development of an organism over a period of time. It is measured as an increase in biomass and is associated with cell division by mitosis, subsequent increases in cell size, and with the differentiation of cells to perform particular functions.


Reproduction is the process of production of progeny possessing features more or less similar to their parents in multicellular organisms. Reproduction in organisms occurs by asexual means also. Fungi multiply and spread easily due to the millions of asexual spores they produce. When it comes to unicellular organisms like bacteria, unicellular algae, reproduction is synonymous with growth.

That is increase in number of cells. There are many organisms which are not able to reproduce for example infertile human couples, mules, sterile worker bees, etc. However, only living organisms have capability to reproduce, not non-living objects.

Reproduction is the natural process among organisms by which new individuals are generated and the species perpetuated.


All living organisms are comprised of chemicals. These chemicals are constantly being made and changed into some other bimolecular. Thousands of metabolism reactions used to occur simultaneously inside all living organisms. It may be unicellular or multicellular.

All plants, animals, fungi and microbes have metabolism. All the chemical reactions occurring in our body is metabolism. Environment senses through sense organs. Plants respond to light, water, temperature, other organisms, pollutants, etc.

All organisms handle chemicals entering their bodies. Human being is the only organism who has self-consciousness. Properties of tissues are not present in the constituent cells, but they arise as a result of interactions among the constituent cells. Living organisms are self-replicating, evolving and self- regulating interactive systems capable of responding to external stimuli.

Metabolism have two stages-catabolism and anabolism. Catabolism is the process of breaking large molecules into small molecules. Anabolism is the process where chemical reactions occur and which lead to production of large molecules by splitting small molecules.

Metabolism is the sum of physical and chemical processes in an organism by which protoplasm is produced, maintained and destroyed, and by which energy is made available for its functioning.

Essential Characteristics of Living Beings

The following points highlight the fifteen essential characteristics of living beings. The characteristics are: 1. Cellular Structure 2. Metabolism 3. Growth 4. Reproduction 5. Consciousness 6. Organisation 7. Energy 8. Homeostasis 9. Variations 10. Adaptations 11. Healing and Repair 12. Disposal of Wastes 13. Movements 14. Life Span 15. Death.

Characteristic # 1. Cellular Structure:

It is defining property of living beings. Each living being is a complex entity which is formed of one or more cells. The cells are made of protoplasm, popularly called living matter. Composition of living matter is known. However, we have not yet been able to create protoplasm because of lack of organisation of biomolecules. Protoplasm and cellular structure are absent in viruses.

Characteristic # 2. Metabolism:

All organisms operate a network of thousands of chemical reactions. The sum total of all chemical reactions occurring in an organism due to specific interactions amongst different types of molecules within the interior of cells is called metabolism (Gk. metabole— change).

Metabolism is defining property of living beings. All activities of an organism including growth, movements, development, responsiveness, reproduction, etc. are due to metabolism. No non-living object shows metabolism.

However, metabolic reactions can be carried out outside the body of an organism in cell free systems. Such reactions are neither living nor non-living. The isolated in vitro metabolic reactions can, however, be called biological reactions or living reactions as they involve bio-chemicals.

Characteristic # 3. Growth:

Growth is irreversible increase in mass of an individual. A multicellular organism increases its mass by cell division. In plants growth continues throughout life as they have meristematic areas where cell divisions occur regularly.

In animals, growth occurs to a certain age after which cells divide only to replace worn out and lost cells. Unicellular organisms also grow by cell division. However, cell division is also a means of reproduction in them. In higher animals and plants, growth and reproduction are mutually exclusive.

Living organisms show internal growth due to addition of materials and formation of cells inside the body. Such a method is called intussusception (L. intus — within, suscipere— to receive). A dead organism does not grow. However, some non-living articles can increase in size, e.g., mountains, boulders, crystals, stones.

It is due to addition of similar materials to their outer surface. The process is called accretion (L. accrescere — to increase). In living beings growth producing substances are of two types, protoplasmic and apoplasmic.

Pro­toplasmic substances are components of living matter like cytoplasm and nucleus. Apoplasmic substances (Gk. apo- away, plastos – formed) are non-living materials formed by the cells which become component of tissues, e.g., cell wall, fibres of connective tissue, matrix of bone and cartilage.

Chemically growth is a result of difference between anabolism and catabolism. Growth occurs when anabolism exceeds catabolism. There will be no growth if anabolism and catabolism are equal. Degrowth or negative growth can occur when catabolism exceeds anabolism.

Characteristic # 4. Reproduction:

It is the formation of new individuals of the similar kind — life arises from pre-existing life. Reproduction is not essential for survival of the individuals. It is required for perpetuation of a population.

Ability for reproduction develops when a young individual becomes mature. Reproduction is of two types, asexual and sexual. Asexual reproduction is uniparental while sexual reproduction is generally bi-parental.

Asexual reproduction is the formation of new individuals from specialised or un-specialised parts of a single parent without the formation and fusion of gametes. It occurs by spores, binary fission, multiple fission, fragmentation and regeneration. Sexual reproduction involves the formation and fusion of two types of sex cells or gametes. The fusion product or zygote gives rise to an offspring.

In unicellular organisms, growth and reproduction are synonyms. Many organisms do not reproduce, e.g., mules, sterile worker bees, infertile human couples. Therefore, repro­duction is not an all inclusive characteristic of living organism. However, no non-living object has the power to reproduce or replicate.

Metabolism is of two kinds, catabolism and anabolism. Anabolism includes all the “building up” reactions.

It is also called constructive metabolism since it involves the synthesis of complex substances from simpler ones, e.g., synthesis of organic compounds from CO2 and HO2 during photosynthesis, formation of starch from glucose, production of proteins from amino acids, formation of lipids from fatty acids and alcohols. Energy is stored (as potential energy) in the process.

Catabolism (= katabolism) constitutes “breakdown reactions”. It is also known as destructive metabolism because it involves breaking of complex substances into simpler ones. Potential energy present in the complex substances is converted into kinetic energy. Respiration is an example of catabolism. It releases energy for performing different body activities.

Differences between Anabolism and Catabolism:

1. It is the sum total of building up or constructive processes.

2. Anabolism produces complex materials from simpler ones.

4. Kinetic energy is changed into potential energy.

5. Anabolism is required for growth, maintenance and storage.

6. Fewer types of precursors form diverse products (reactions diverge).

1. Catabolism is the sum total of breakdown or destructive processes.

2. It forms simple substances from complex ones.

4. Potential energy is changed into kinetic energy.

5. Catabolism is required for performing various activities of living beings.

6. Many types of larger substances breakdown to form fewer types of simple molecules (reactions converge).

Characteristic # 5. Consciousness:

It is awareness of the surroundings and response to external stimuli. The external stimuli can be physical, chemical or biological. The stimuli are per­ceived by sense organs in higher animals, e.g., eyes, ears, nose. Plants do not possess such sophisticated sense organs.

However, they do respond to external factors such as light, water, temperature, pollutants, other organisms, etc. Photoperiods (duration of daily ex­posure to light) influence reproduction in those animals and plants which breed during particular season (seasonal breeders).

All organisms, from primitive prokaryotes to most advanced and complex eukaryotes, are able to sense and respond to environmental factors. Organisms also handle chemicals entering their bodies. Human beings have an additional faculty of self consciousness (aware­ness of self). Consciousness is said to be the defining property of living organisms.

If a patient is lying in coma and is supported by machines for various functions, self consciousness and consciousness to external environment are supposed to be absent. Some of these patients never come back to normal life. They can neither be called living nor non-living or dead.

Characteristic # 6. Organisation:

A living being has an organisation, that is, the living being consists of several components and subcomponents which cooperate with one another for the well being of the whole organism. A living being has multiple level organisations.

Each level of organisation has its own properties which are not found in its constituents. A cellular or­ganelle develops a property not found in its interacting molecular components. A living cell has its own characteristics not found in its organelles. A tissue is able to have a trait not found in its constituent cells.

Characteristic # 7. Energy:

Living beings constantly require energy not only to perform various activities of the body but also to overcome entropy or tendency to randomness. The source of energy is food. It is required by every cell of the body.

Characteristic # 8. Homeostasis (Homoeostasis):

A favourable internal environment suitable for the functioning of body organs is present in every living being. It is quite different from the external environment.

Changes in external environment do not have much impact on the internal environment as the living beings have a self regulated system to adjust and maintain the internal environment. The phenomenon is called homeostasis (Gk. homois — alike, stasis standing). Homeostasis is also present in each cell of a multicellular organism.

Characteristic # 9. Variations:

Living beings possess variations and have the ability to evolve with time.

Characteristic # 10. Adaptations (L. ad— toward, apt— adjust):

Useful inheritable variations or changes inform, function and behaviour which help an organism to adjust well and successfully in its environment are called adaptations. An organism is considered best adapted to an envi­ronment when it possesses inherited traits that enhance its survival and ability to reproduce in that environment.

Adaptations allow the organisms to overcome seasonal and other changes in the environment. They are of two types, short term adaptations (e.g., hiber­nation in most amphibians and reptiles and some mammals) and long term adaptations (e.g., the claws of different birds are well adapted to suit their perching habits).

Characteristic # 11. Healing and Repair:

Living beings can repair and heal the broken and injured parts.

Characteristic # 12. Disposal of Wastes:

Wastes generated by living beings are regularly disposed off.

Characteristic # 13. Movements:

Living beings show movements of their parts. Some are able to move from place to place. The phenomenon is called locomotion.

Characteristic # 14. Life Span:

Every living organism has a definite life span of birth, growth, maturity, senescence and death.

Characteristic # 15. Death:

The stoppage of various life activities by an individual organism accompanied by increase in entropy is called death. Death occurs due to ageing, disease, accident and predation.

Ageing normally occurs in all organisms after a period of reproductive maturity. It is, however, absent in some cases where the organism multiplies by binary fission, e.g., Amoeba, bacteria. A fully grown Amoeba or a bacterium divides into two daughters. In the process it loses its independent existence. Here, natural death is absent and the organism is immortal.

Living organisms are, therefore, self replicating, evolving and self regulatory interactive systems capable of responding to external stimuli, sharing a common genetic material to varying degree both horizontally and vertically.

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What is the difference between animate and inanimate matter? What animates living organisms?

Since the beginning of time, our world has been constantly evolving and changing its structure. From a lifeless, inhabitable mass of rocks to a planet full of life of all kinds, our Earth is home to both animate and inanimate matter. Yet where does one draw the line to decide what is alive and what is not? Who decides what constitutes life? This has always been a very challenging question in my opinion, because its implications are imperative for the decisions that people make when thinking about animal cruelty, abortion, veganism, and many more topics. If we have the answer, can we then find a recipe for it? If we can, then we would come up with a modular approach that would allow us to model life in an even more complex way, since we would be able to modify specific parts of the recipe to suit our needs.

First of all, we are aware that all life is made up of carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (Wolchover). This gives us grounds to determine that if we’re looking at a specific object, in most cases, if it doesn’t contain these elements, then it cannot be considered alive. These elements all play an important role in creating organisms. Carbon atoms easily form bonds, which are great to form large building blocks of organic molecules and create the first layer of complexity. Nitrogen, hydrogen, and oxygen are very abundant, which makes them easily retrievable from the environment. Further, they bond with carbon to produce amino acids, lipids, and nucleobases, from which RNA and DNA are built (Wolchover). Phosphorous is instead vital to metabolism due to polyphosphate molecules, such as ATP, being able to store huge amounts of energy (Wolchover). Finally, sulfur is essential by catalyzing reactions thanks to shuffling its electron surplus.

Yet, there have been some exceptions to this basic structure. For example, NASA scientists were able to find a strain of microbes in an arsenic-rich lake in California that used arsenic instead of phosphorous thanks to the abundance of the former and scarcity of the latter. In other cases, organisms use selenium instead of sulfur, but that is also not very common. Despite the mainly firm structure that a living organism has to follow, there are surely other main factors that come into play that make life happen on Earth. These include the right distance of our planet from the sun, an atmosphere with oxygen, an abundant supply of water, and the occasional burst of energy created from lightning to help catalyze reactions. All of these factors are at least essential for life how we know it, but what if there are other forms of life in our universe?

For all we know, animate alien organisms may have a completely different aspect, form and set of characteristics from what we are used to on Earth. But then by our standards, would they not still be considered inanimate? If we think about this from the perspective of an alien species, what if we are considered inanimate in their eyes? Perhaps for species X, an animate organism needs to have eight eyes, three hearts and the ability to jump thirty feet and breakdance at the same time. Then is there a universal way for something to be considered alive? This goes back to the question of how we choose to define life.

An object is to be considered alive if it contains the following. An organizational structure that divides the roles for each part to execute a metabolism to carry out chemical reactions to do work homeostasis to oversee the general status of the organism the ability to grow and reproduce the capacity to respond to environmental changes and to evolve and adapt in order to maximize life expectancy (Khan Academy). The list is definitely exhaustive and includes many parts, yet it’s not definite as there always are exceptions that make this such a deep question. For example, viruses have many of the properties previously described to make them alive, yet they don’t possess cellular structure nor they can reproduce without a host. Therefore, should we consider them alive or are they simply carrying out mechanical tasks, purely caused by the works of chemistry?

The main distinction to make is now between being animate and alive or inanimate and alive (whereas previously I was referring to animate as in a living being and inanimate as a non-living object). In this case, given an object is alive, it is also animate if it is conscious of what it is doing, feeling and thinking and this is an essential difference. Consciousness plays a fundamental role in distinguishing the two because it’s the essence that makes human life extraordinary when compared to, say, bacteria, insects or plants.

A different line of thought instead shines light on a different aspect of the dilemma. At their core, atoms are all inanimate. In fact, there is no difference between an oxygen atom present in the air and an oxygen atom being used by our lungs when we breathe. From this point of view, one will then want to ask when is it that particles go from being inanimate, to animate. Chemically, life arises from a combination of reactions that prove to be successful in keeping the genes of a specific organism transcend time. So where does the switch happen? In my opinion, it does not. There is no line to be crossed because there is no one factor that is responsible for what we call life. I believe we instead lie on a spectrum that ranges from most inanimate (an atom of hydrogen) to most animate (a human being) and that we cannot physically determine when that transaction happens. We can also think about this from a perspective that takes life into account only as a whole. For example, is a person’s leg animate or is it inanimate? Is a brain animate? The only possible answer that I can see to this question comes purely from societal and philosophical views, instead of physical ones, since I believe we don’t have the tools to make such distinction.

Therefore I believe the difference between animate and inanimate matter is ultimately none, as all matter is inanimate. What really makes the difference is the system in which such matter is present in, and how it interacts with its environment to “animate” the organism it is found present in. Even though all singular components of the organism can be considered inanimate on their own, it’s their combination that creates the life that we are so in awe from — the whole is greater than the sum of its singular parts. In regards to what animates living matter, consciousness is the determining factor, and we are still far from finding out this mysterious part of our life is made out of. Yet that is what I think to be the most beautiful part of life. The delicate, creative, subtle variances that matter possesses to present itself in our world in so many different forms and states. Whether it is animate or inanimate, life will always be something special and to profoundly cherish, as, for all we know, there may be none like ours anywhere else.

Opinion: How to Define Life

John D. Loike and Robert Pollack
May 2, 2019

C ase Western Reserve University researchers are moving toward creating robots with superior emotional intelligence. They’re advancing artificial intelligence (AI) to create next-gen personalized robots that can read human emotions in real time. What will be the next step in AI robots? If they can be developed to mimic biological life, do we confer the status of living creatures on them? Do we confer personhood as well?

The development of biocomputers that use strands of nucleic acid to perform rapid parallel computations and human-like robots with artificial intelligence, such as Sophia, are exciting technological endeavors that require scientists to define life. In fact, some countries, including Saudi Arabia, have given robots like Sophia national citizenship. At the same time, innovative technologies in synthetic biology present new challenges to life as it exists today. Scientists are now creating organisms that incorporate synthetic letters of our DNA that expand the four classical nucleotides to a six- or eight-nucleotide alphabet. How should we view the status of bacteria designed with an expanded synthetic DNA code? A precise definition of biological life has been discussed and debated over several hundred years, without a clear conclusion.

Read The Scientist’s special issue on artificial intelligence.

The endeavor to define biological life is more than an academic exercise. One could argue that definitions only tell us about the meanings of words in our language, as opposed to telling us about the nature of the world. With respect to defining living personhood, there are of course additional legal as well as moral implications that must be considered and are beyond the scope of this article. Nevertheless, our moral imperatives in large measure depend on how we define life.

Historically, characterizing a precise definition of life is generally based on unique characteristics of all known living organisms. For example, according to current notions of life, living organisms must: a) have a biological genetic set of instructions (ours are found in DNA and RNA) that encodes and regulates its functional properties b) be composed of individual units or cells surrounded by a plasma membrane and that contain and metabolize biological entities, such as nucleic acids, proteins, carbohydrates, and lipids c) be capable of adaptation or mutation to alter their phenotypes and respond to environmental factors that can alter their genotypes or phenotypes d) undergo metabolic homeostasis—regulated growth that responds to both internal and external environments in response to external environmental conditions and e) reproduce to create new organisms and have finite lifetimes. Organisms created from synthetic nucleotides, and AI-based robots, may not fit all these criteria.

In our definition, organisms that utilize synthetic DNA nucleotides may meet our criteria as living.

For natural selection to have generated such a diversity of living things on earth, time and the mortality of every individual organism to assure the future survival of species are both required. We propose a simple but challenging definition of life as the property of an organism that possesses any genetic code that allows for reproduction, natural selection, and individual mortality.

This definition underscores the need to protect the unknowability of future life forms. The randomness of pre-adaptive mutation, the surviving genomes, and the phenotypes of our species in the future cannot be known with certainty, nor can we know what species will replace us, if any.

Our definition is more expansive than NASA’s, which describes life as “a self-sustaining chemical system capable of Darwinian evolution.” AI robots would not fit into our definition because human beings can control all aspects of computer functions. There is no uncertainty, nor unknowability, with AI robots. AI-based human robots can be programed to replicate themselves and even can be programed to terminate. However, robots do not sense “mutations” or engage in any natural selection process and, therefore, would not meet our criteria as “living.”

In our definition, organisms that utilize synthetic DNA nucleotides may meet our criteria as living. However, it is important to recognize that while developing synthetic “life forms” constitutes technologically exciting endeavors, the danger that they may destroy all existing life forms on Earth through the unpredictability of natural selection may push such projects across an ethical boundary.

We argue that as living organisms, and, in particular, as mortal creatures who are aware of our own mortality and of our capacity and obligation to distinguish right from wrong, we must recognize this boundary between living and inanimate. We believe the definition we have presented creates a clean boundary around all living things that allows us to assess the living status of synthetic organisms and AI robots.

John D. Loike, a professor of biology at Touro College and University Systems, writes a regular column on bioethics for The Scientist. Robert Pollack is a professor of biological sciences at Columbia University.

Cell Sentience Challenges Neo-Darwinism

In his book, Evolution: A View from the 21st Century, 33 James A. Shapiro, Professor in the Department of Biochemistry and Molecular Biology at the University of Chicago, provided ample examples where molecular biology has recognized cell cognition from cell sensing, information transfer, decision-making processes. In this book Shapiro, thoroughly dismisses the traditional Neo-Darwinian evolution theory that is widely accepted by biologists. In Darwinism, organisms are often assumed as optimally designed machines blindly engineered by natural selection. However, based on cell cognition, Shapiro challenges that view:

“Given the exemplary status of biological evolution, we can anticipate that a paradigm shift in our understanding of that subject will have repercussions far outside the life sciences. A shift from thinking about gradual selection of localized random changes to sudden genome restructuring by sensory network-influenced cell systems is a major conceptual change. It replaces the “invisible hands” of geological time and natural selection with cognitive networks and cellular functions for self-modification. The emphasis is systemic rather than atomistic and information-based rather than stochastic.” (Page 145 in). 33

In recent time Neo-Darwinian evolution theory is facing several challenges from various corners 34,35 and hence, it is the right time to find the proper alternative explanation for biological evolution, based on cognitive principles.

Figure 4. Polar bears (Ursus maritimus) and other mammals living in ice-covered regions maintain their body temperature by generating heat and reducing heat loss through thick fur and a dense layer of fat under their skin. (credit: “longhorndave”/Flickr)

In order to function properly, cells need to have appropriate conditions such as proper temperature, pH, and appropriate concentration of diverse chemicals. These conditions may, however, change from one moment to the next. Organisms are able to maintain internal conditions within a narrow range almost constantly, despite environmental changes, through homeostasis (literally, “steady state”)—the ability of an organism to maintain constant internal conditions. For example, an organism needs to regulate body temperature through a process known as thermoregulation. Organisms that live in cold climates, such as the polar bear (Figure 4), have body structures that help them withstand low temperatures and conserve body heat. Structures that aid in this type of insulation include fur, feathers, blubber, and fat. In hot climates, organisms have methods (such as perspiration in humans or panting in dogs) that help them to shed excess body heat.

Figure 5. The California condor (Gymnogyps californianus) uses chemical energy derived from food to power flight. California condors are an endangered species. This bird has a wing tag that helps biologists identify the individual.

Is Consciousness a Property of Everything in the Universe?

Where does consciousness come from? The traditional view, believed by the 6 billion people in the world who belong to religions that assume life after death, is that humans consists of two different kinds of things, a body and a soul. The materialist view, held by many contemporary neuroscientists and psychologists and an increasing number of philosophers, is that the human mind is the brain. On this view the mind is a purely physical system and expires when the body does.

Recently, however, there is been a revival of a less familiar position called panpsychism. Panpsychism is the claim that consciousness is not just a property of the brain, and not a property of some special spiritual kind of substance like the soul, but rather a property of everything in the universe. Even a rock or a pebble or an atom has a little bit of consciousness in it. Panpsychism has been endorsed by two distinguished neuroscientists, Christof Koch and Guilio Tononi. Why would anyone hold this view?

The main support for panpsychism seems to be a kind of argument from ignorance. It seems mysterious how the peculiar properties of consciousness such as awareness and feeling could result from anything physical. This kind of incomprehensibility, along with religious motivations, has traditionally been used to support dualism, the idea that a person consists of two separate things, mind and soul. But with the lack of any evidence for the existence of souls, and the waning of religious beliefs, some people favor panpsychism over dualism. We just can't see how it is that properties like experience and awareness could result from the mere motions of molecules. So there must be a little bit of consciousness in everything that can then sum up to the experiences found in humans.

I think that there are many flaws with this line of reasoning. It neglects the importance of emergence, which I wrote about in a previous blog post. The natural world contains many cases where wholes have properties that are very different from the properties of their parts. A water molecule consisting of hydrogen and oxygen has properties such as being liquid at room temperature that are not found in hydrogen atoms or oxygen atoms. To take a more complicated example, consider life. Atoms and molecules are not alive, but cells and single cell organisms and much more complicated plants and animals possess life. In the 19th century, it was commonly thought that life is so different from nonliving things that there must be a special property, called life force, that belongs only to living things and distinguishes them from those things that are not alive. In the 20th century, however, it became widely recognized that life is not a special property, but rather the result of many mechanisms, such as genetics, metabolism, cell division, and reproduction. Analogously, consciousness could be an emergent property of neural mechanisms.

Curiously, no one ever proposed a life-oriented analog of panpsychism, which one might dub “panlifeism”, to say that in order to explain life we must think that there are bits of life in everything that exists. The reason that panlifeism never was proposed was the rapid progress made in 20th century biology as more and more of the details of how life works at the material level became revealed. We do not yet have nearly as good an account of the biological mechanisms of consciousness that we have for the mechanisms that support life. This ignorance allows room for people to propose panpsychism as an alternative to what I think is the more plausible account that conscious minds are neural processes.

However, we only have good evidence for the existence of consciousness in organisms that have brains. I know that I am conscious because of my own experience of awareness, sensation and emotion. It is reasonable for me to extend consciousness to other people because that ascription is the best explanation of their behavior which is very similar to mine. Additional support comes from realizing that other people have pretty much the same kind of brains as me. It is then reasonable to further extend description of consciousness to other organisms that have somewhat similar behaviors and similar brain structure to those of humans, for example mammals. The neural circuitry and the behavior of mammals supports the view that their experience of pain and emotions such as fear have a lot in common with the experiences of human beings. It may be reasonable to suppose that fish feel pain as well, has been argued convincingly in a book by the Victoria Braithwaite. But there is no behavioral evidence at all that trees or rocks or pebbles or atoms have even a tiny bit of consciousness.

In contrast, consciousness is plausibly an emergent property of brains. Consciousness is not a property of individual neurons but results from the interactions of many neurons, in the same way that life results from the interactions of many molecules. I propose in a new article that the most important neural mechanisms for producing consciousness are the following three. First, there are representations such as CAT accomplished by the interactions of large numbers of neurons. Second, these representations can generate more complex kinds of representations by a process of binding, for example producing BLACK CAT. To get to the full level of representation that humans are capable of we need to have the capacity for bindings of bindings of bindings, that is representations of representations of representations, as in THE BLACK CAT CHASED THE WHITE MOUSE. Finally the third mechanism that I think is responsible for consciousness is competition, which allows only a small subset of the available information to be active in the brain as sufficiently important to win out over other representations.

It remains to be seen whether these three mechanisms are in fact responsible for the major phenomena that need to be explained by a theory of consciousness. But if I'm on the right track, then we don't need to extend attribution of consciousness all the way down to every bit the universe. Consciousness is an emergent property of special kinds of complex systems, namely large groups of neurons. Perhaps, consciousness might also turn out to be a property of other kinds of extremely complex systems, for example ones that operate in computers. But if computers ever turn out to be conscious, I suspect that it will result from having approximate analogs of the three kinds of mechanisms that I think make consciousness working human beings: representation, repeated binding, and competition among complex representations. Once this more sophisticated account of consciousness has been developed, there will no need to suppose that there is even a tiny bit of consciousness in various bits of the universe other than brains and similarly complex systems.

The ubiquity of consciousness

In his essay, What about ‘information’?, Massimo Pigliucci (2011) makes an eloquent argument to counter the claims of supporters of intelligent design, who argue that the evolution of intelligence must have been guided by some supernatural force. But, in making his case, he states that “only humans and other relevantly similar conscious organisms have knowledge”. He is certainly not the only one who considers that ‘knowledge’ and consciousness are qualities unique to highly developed species such as humans, dolphins or higher apes, denying them to the vast majority of species and organisms on Earth.

“In the simplest sense, consciousness is an awareness […] of the outside world”

However, many definitions of consciousness and intelligence are inevitably anthropocentric and therefore hamper our efforts to see these qualities in other species. Lynn Margulis, author of the endosymbiotic theory of organelle evolution, provides a more inclusive definition of consciousness and intelligence: “Not just animals are conscious but every organized being is conscious. In the simplest sense, consciousness is an awareness (has knowledge) of the outside world” ( Margulis & Sagan, 1995 ). Similarly, the Chilean biologist and philosopher Humberto Maturana wrote that “Living systems are cognitive systems and living as a process is a process of cognition. This statement is valid for all organisms with and without a nervous system” ( Maturana, 1970 ). Cognition here refers to the behaviour of any living system in relation to its environment. These debates still reflect common attitudes of the early twentieth century that regarded most organisms as mechanistic—even mechanical—systems that blindly follow predetermined programmes of behaviour supposedly inscribed in their genes. Modern views instead emphasize plasticity in development and behaviour that counter these mechanistic misunderstandings.

Donald Griffin (1915–2003), who spent his career researching animal behaviour, was the most cogent and early critic of anthropocentric definitions of intelligence and consciousness. Consciousness in any other organism cannot be directly ascertained, he maintained, because of our inability to communicate, to ask relevant questions. But failure to communicate does not mean the absence of any capability instead, we need to analyse the types of communication of which organisms are capable. In fact, on what experimental evidence, other than supposition, do we reject consciousness in other organisms?

Awareness (consciousness) confers a significant adaptive advantage that enables organisms to react appropriately to physical, biological and social signals from their environment. Mechanistic beliefs assume that behaviour is simple and most organisms merely show reflexes. This attitude is the result of experimental investigations that force organisms to behave in particular ways and have led to erroneous conclusions about the behaviour of organisms in their natural environments. Griffin, by contrast, adamantly denied such mechanistic attitudes. “The crippling limitations of such intellectual myopia should be clearly apparent the simplicity lies not in the behaviour but in its description,” he wrote ( Griffin, 1976 ). This view is echoed by Kevin Warwick, a British scientist working on artificial intelligence: “I believe that dogs and cats are conscious in their own way, and bees, ants and spiders are conscious, not as humans but as bees, ants and spiders. I cannot say that a robot with a computer for a brain is not conscious because its brain is not like mine and because it thinks in a different way to me” ( Warwick, 2000 ).

Only ‘wild’ behaviour in the natural environment is really meaningful for observing conscious, intelligent behaviour

More generally, we regard intelligent behaviour as the capacity for solving problems and consider it to be inextricably linked to evolutionary fitness. The German biochemist and Nobel laureate Manfred Eigen, provides definitions of learning, memory and intelligence at the molecular level that suggest how organisms might have evolved such behaviours ( Eigen & de Maeyer, 1966 ). Clearly, not every behavioural trait is a sign of intelligence, but when the environment is unpredictable in terms of food resources or the presence of predators, innate behaviour is maladaptive and threatens survival. Fitness favours those organisms that can adapt.

The ability to learn from experience and adapt behaviour accordingly is most apparent among the higher vertebrates. Teaching a chimpanzee 300 words using sign language or observing that chimps stack boxes to reach a hanging banana are indeed impressive, but these are still experimental designs that impose human criteria of consciousness and intelligence. Chimpanzees can take hours, days or months to learn how to solve some laboratory problems, but they need only seconds to learn a particular dominance status when they encounter a new social situation. Only ‘wild’ behaviour in the natural environment is really meaningful for observing conscious, intelligent behaviour.

Until now, the research animal most endowed with human qualities was a grey parrot named Alex, trained by Irene Pepperberg and her collaborators ( Alex had a spoken language of about 100 words, understood abstract terms, such as shape—smaller, larger, same, different—could count to six, and could identify many colours. He learnt to ask for things and would reject them if they were not what he wanted. He had a remarkable understanding of the properties of particular objects and could identify the materials from which they were made. He could assess the properties of new objects even if he had not seen the specific combination of materials before. Most remarkably, he could apologize if he annoyed his trainer. Alex was clearly conscious and intelligent. Birds and mammals evolved from evolutionary branches that separated several hundred million years ago. Thus intelligent behaviour in these organisms has arisen separately, a portent for potential intelligent behaviour in other organisms.

Corvids—ravens, crows or jays—also exhibit intelligent behaviour within their natural environment ( Heinrich & Bungnyar, 2007 Seed et al, 2008 ). Seed caching is common among corvids and indicates foresight. Jays can remember the precise position of thousands of seeds through cognitive maps that they construct when they hide their stash. If competitors observe them preparing their cache, they will move it privately later, but only if they themselves have previously pilfered another bird's seed cache. When presented with food hanging from the end of a long string attached to their perch, ravens solve the problem by drawing up the food using beak and claw after a few minutes thought and without any trial and error. This is a clear case of abstract thinking. Different ravens come up with a variety of solutions to this simple puzzle. If one raven finds the food too heavy, it will recruit a mate for help and the speed of recruitment is determined by the closeness of the relationship between the two. Crows use sticks to probe holes for insects. Given a choice, they immediately select the stick with the right diameter for the appropriate hole. When presented with food at the bottom of a tube too deep to reach with the beak, one crow has been observed to bend a piece of wire into a hook to pull up the food. In experimental situations, crows will follow the direction of the experimentalist's gaze. Ravens have also been seen to console other distressed ravens. These birds clearly show self-awareness, intelligence and consciousness. Abilities have to be judged not on the details of behaviour—by use of beak and claw, rather than opposable thumbs—but on whether the problem is solved, by whatever the means. To assume otherwise is to judge subjectively ( Warwick, 2000 ).

“It is not too much to say that a bee colony is capable of cognition in much the same sense that a human being is”

The fact that intelligent behaviour is apparent in higher apes, corvids and parrots suggests that social interactions might be a prerequisite for consciousness and intelligence. All these animals live in groups or flocks, so social interaction is inevitable. Similarly, human intelligence evolved among our ancestors through the positive feedback implicit in social interactions. But there are many other organisms, including microorganisms, that have adopted social lifestyles—indeed multicellular organisms can be regarded as colonies of socially interacting cells—and that could benefit from intelligent behaviour through social interaction.

The most thoroughly investigated of the social ‘lower’ life forms are ants and bees. Their self-organizing interactions construct an emergent ‘swarm intelligence’. “It is not too much to say that a bee colony is capable of cognition in much the same sense that a human being is. The colony gathers and continually updates diverse information about its surroundings, combines this with information about its internal state and makes decisions that reconcile its well being with its environment” ( Seeley & Levien, 1987 ). Is the colony—or the ‘super-organism’ it represents—both intelligent and conscious? Can one exist without the other?

As all biological systems—including insect colonies—are networks with varying degrees of complexity, the question is rather whether such swarm intelligence networks are too simple to express more sophisticated ‘intelligence’? Detailed examination of individual insect behaviour suggests that neither colonies nor insects are simple systems ( Griffin, 1976 ). The physical and acoustic ‘dance’ performed by a returning bee conveys detailed knowledge and integrates information from both outside and inside the hive. There is evidence that a few leaders then recruit worker bees that have seen the dance to the new origin of food, while many other workers who also saw the dance continue with their previous tasks. In a similar fashion, experienced foraging ants lead naive nest mates in the right direction to food or a new nest site. This “was the first case in which teaching, as strictly defined, was shown in a non-human animal” ( Franks & Richardson, 2006 ).

Usually, a few scouts—ants and bees—investigate new nest sites, assess the level of suitability and convey that information quantitatively to others. Ant scouts actually measure the internal size of a new nest and assess the suitability of possible entrances. They further examine the new site until a ‘quorum of approval’ results in a decision to move, led, of course, by scouts. Poor sites take longer for approval. What constitutes the threshold for approval and the subsequent move is not understood.

Individual bees process information using spatial and counting memories and can recognize images of complex natural scenes with very fine discrimination. Experimental investigations show that bees exhibit associative recall categorize and interpolate visual information master abstract relationships such as sameness and difference group together similarly shaped objects and learn contextual information ( Giurfa et al, 2001 Gross et al, 2009 ). Bees can generalize simple learning exercises and adapt them to new situations they can learn to fly through mazes via spatial landmarks, transferring that memory of marks to new mazes, and using landmarks and landscape structure to estimate distance and hive position. Alternatively, if trained at a specific time of day with an orientation cue, they can recall this information to navigate new mazes in the absence of orientation information. “A bee knows what to do, when and also where” ( Pahl et al, 2007 ). They can subitize, that is, assess at a glance a quantity of items up to four ( Gross et al, 2009 )—note that the limit for humans is between four and seven. Individual bees were trained to extend their proboscis into a drop of sugar solution when it was offered. By providing the drop at defined intervals, each bee rapidly learnt to predict when the next drop would appear and extended its proboscis in anticipation. Thus bees have a sense of the future and a memory of the past. Bees can also prioritize flower visits and optimize costs (flying time) against benefits (nectar yields). After training, bees can discriminate bilateral symmetry from non-symmetrical patterns, transfer the experience to other situations and recognize bilateral axis rotation. Finally, ants and bees can choose to make a trade-off between speed and accuracy. They also acquire long-term memories of past experience because frequent movement to different sites progressively reduces the total move time.

Are these organisms self-aware? Ants do not attack other nest mates but will attack other nests of the same species. Bees will attack hive intruders including other genotypes and recruit others to the attack by means of pheromones. All of this demonstrates perception and awareness of self, compared with other bee genotypes and non-nest members.

Even ‘simpler’ organisms show signs of self-awareness. Species of the sea anemone Actinaria often reproduce through cloning if two clones contact each other, they fight to establish supremacy leaving a distinctive anemone-free zone between them. Clone colonies contain ‘warrior’ polyps along the borders and larger reproductive types deeper in the colony with five intergrading castes.

“It is puzzling that primitive organisms that lack any kind of nervous system show sophisticated behaviours that we assume require a nervous system. Many examples noted in the past belie this assumption” ( Bonner, 2010 ). This statement introduced experimental observations of the slime mould Physarum that demonstrated its ability to discriminate between a great variety of food sources and to explore only those that provide the optimal diet for growth. Physarum can also navigate a maze to connect the shortest distance between food and its present position some argue that such properties indicate a primitive intelligence ( Nakagaki et al, 2000 ). By using minimal path length and optimal tube thickness, Physarum minimizes energy expenditure for maximal energy gain. When subjected to shocks at periodic intervals, Physarum remembers the frequency and is able to predict the appearance of the next one “hinting at the origin of intelligence” ( Ball, 2008 ). When required to behave more quickly, the slime mould makes more mistakes, which indicates trade-offs between speed and accuracy.

Such apparent signs of learning and consideration are not confined to slime moulds and other primitive multicellular organisms, but can also be observed in protozoans. When Paramecia are confined to tubes smaller in diameter than the length of the protozoan, they initially require a few minutes to turn with some practice, the cells become capable of turning in a few seconds—an observation that indicates learning in a single-cell protozoan. In a study in the 1920s, other protozoans including Stentor, Didinium and Amoeba showed a surprising variety of behaviours ( Jennings, 1923 ), leading the author to conclude that because their behaviour could be modified by experience, it was surely a sign of intelligence. Moreover, as this learning behaviour was objectively similar to that of mankind, Jennings suggested that consciousness is distributed throughout the animal kingdom. Some amoebae and other protists build protective and elaborate enveloping cases (houses) from gathered material. This and other observations on the behaviour of Amoeba led Walker (2005) to conclude that “Amoeba perceives, recognizes, chooses and ingests a variety of prey that is not much short of the choice of higher animals, it recognizes its own kind and engages in cooperative behaviour,” particularly in cooperative hunting. Recognition of its own kind would indicate that amoebae are self-aware.

“It is puzzling that primitive organisms that lack any kind of nervous system show sophisticated behaviours that we assume require a nervous system”

So, what about bacteria, the simplest of all cells? Four aspects of bacterial behaviour have received much attention so far: chemotaxis, signal transduction, quorum sensing and the formation of large morphologies. Bacterial signal transduction—more than 50 signals have so far been identified—is controlled by a phosphoneural network in which changes in phosphorylation create or break network connections, thereby acting as logical operators ( Hellingwerf, 2005 ). This process is analogous to changes in dendritic connections in the brain and it enables bacteria to make ‘informed decisions’. Autoamplification of parts of the network in response to environmental signals results in ‘learning behaviour’ ( Hellingwerf, 2005 ). “Some of the most basic properties of brains such as sensory integration, memory, decision-making and the control of behaviour can all be found in these simple organisms” ( Allmann, 1999 ).

…bacteria anticipate predictable changes in their environment with a clear sense of both time and space and their immediate neighbours

Bacteria also communicate with each other in a variety of ways. Biofilm formation and quorum sensing lead to changes in bacterial behaviour when a quorum is reached, similarly to the behaviour of social insects. Self-identity and social recognition—that is, awareness of members of their own species—has also been observed ( Gibbs et al, 2008 ). Under conditions of starvation or on hard surfaces, bacterial populations self-organize into highly structured morphologies that are thought to represent survival strategies. These morphologies can originate from travelling waves of motile bacteria that enable individual cells to find appropriate environments. The structured colony is capable of collective sensing and communication through large or small molecules, distributed information processing and collective gene regulation these are yet more examples of cognitive functions and social intelligence.

The bacterial cell can therefore no longer be regarded as a simple, self-contained bag of enzymes supposedly less complex than eukaryotes. Instead, bacteria anticipate predictable changes in their environment with a clear sense of both time and space and their immediate neighbours. They also modify their living space to their own advantage.

At what level of complexity and communication do networks become conscious? Any network able to control its own behaviour by changing connection strengths, storing acquired information, redirecting information flow and recognizing its own kind compared with others would fit the necessary criteria the obvious analogy between bacterial behaviour with swarm intelligence underpins the notion that the collective behaviour of bacterial colonies shows signs of both consciousness and intelligence.

Finally, can we also observe consciousness, self-awareness and intelligence among plants? This is more challenging because experimental observations of plant behaviour are hampered by various factors: higher plants develop on a much slower timescale than most animals the experience of most scientists and the public is with domesticated plants in laboratory or garden environments, whereas intelligent behaviour requires observations in the wild a crucial part of plant behaviour takes place below ground.

To address plant intelligence, we therefore have to look at plants in their natural environments where they need to maximize the acquisition of patchily distributed resources, deny them to competitors and minimize predation and disease because seed number and thus fitness is determined by accumulated reserves. Went & Thimann (1937) concluded that “in tropic movements (to light and gravity) plants appear to exhibit a kind of intelligence their movement is of subsequent advantage to them” indicating fitness criteria for intelligence. Went was the discoverer of auxin, a crucial plant hormone. Fitness also includes a choice of partners: “There is good evidence that plants can choose their mating partners—they just do it differently from animals” ( Moore & Pannell, 2010 ).

Generally, plants are constructed from populations of competing and cooperating meristems. Individual meristems sense and pursue resource gradients and forage by proliferating local meristems into rich resource patches, thereby adapting the phenotype. But the overall behaviour of an individual plant is much more integrated and coordinated to optimize fitness. The cambium in the shoot, a meristematic inner skin, continually assesses and integrates the productive behaviour of all shoot branches. The pericycle and cambium fulfil a similar function in the root. The plant generates vascular tissue to supply shoot branches with more root resources that are predicted to be more productive in terms of carbohydrate production and other leaf functions ( Novoplansky, 2003 ), whereas less productive branches lose vascular elements—this strategy is crucial in the plants’ competition for light. Another sensory mechanism measures the distance to the shoots of competitors so the plant can take predictive actions by outgrowing the competition before experiencing any loss of photosynthetic yield.

…“in tropic movements … plants appear to exhibit a kind of intelligence their movement is of subsequent advantage to them”…

“To paraphrase Seeley and Levien (1987) , it is not too much to say that a plant is capable of cognition in the same way that a human being is. The plant gathers and continually updates diverse information about its surroundings, combines this with internal information about its internal state and makes decisions that reconcile its well-being with the environment” ( Trewavas, 2009 ). Again, there are analogies in behaviour between social insect colonies (swarm intelligence) and higher plant behaviour.

At least 20 biological, physical, chemical and electrical plant signals that lead to phenotypic changes have been identified with discrimination on the length, direction and intensity of the signal. Most signals induce a memory that can last, depending on the signal, for hours or days, or even up to years in the case of ‘priming’ against pest resistance. Once learnt, these memories usually ensure a much quicker and more forceful response to subsequent signalling ( Trewavas, 2009 ). Through crosstalk, some memories become associative, inducing specific cellular changes. If one plant is attacked by insects, for example, it releases specifically synthesized volatiles that are sensed by other local plants, which then initiate the synthesis of defence mechanisms to pre-empt attack ( Dicke, 2009 ).

Parasitic plants sense their potential host through released volatiles and capture their prey by following the scent gradient. In the first few hours of contact, the parasite makes an assessment of the future resources that can be gained from the host. If these are insufficient, contact is severed. If the resources are sufficient for exploitation, the parasite calculates the minimal energy outlay to ensure maximal energy gain and specifies the extent to which it needs to develop its haustoria—the resource-acquiring structures. Thus, parasitic plants optimally forage their host in accordance with the marginal value model of animal feeding. Carnivorous plants also show choice over their ‘prey’, as do climbing plants that discriminate between the characteristics of their supporting material.

“A frank unbiased study of consciousness must convince every biologist that it is one of the fundamental phenomena of at least all animal life if not, as is quite possible, of all life”

There are many more signals, the identity of which remain to be uncovered. The growing roots of an individual plant spread apart in the soil on the basis of a strategy of self-inhibition. The plant uses sensing mechanisms to construct a spatial map of the local soil and identify inanimate objects, directing growth away before contact ( Falik et al, 2005 ). Detection of competitive, genotypically related individuals locally in the soil leads to an increase and redirection of root proliferation away from the competitor, often leaving a band of unoccupied soil between them: brethren will not occupy the other individual's territory, but will take action to maximally exploit their own. Separation of one individual plant into several clones results in a rapid loss of each sibling's original self-identity. When grown together, each sibling now comes to regard the others as competitors and exhibits a typical territorial response ( Gruntman & Novoplansky, 2004 ). However, kin recognition is retained in some plants, as competition with strangers is fiercer than with cloned siblings.

Finally, soil mycorrhizae form ubiquitous symbiotic associations with the roots of most higher plants. Their hyphal connections create communication networks as extensive as whole forests in size through which not only water, nitrate and potassium move from plant to neighbouring plant, but also information is conveyed indicating disease or predator attack, thereby enabling plants to prepare complex defence mechanisms even before an attack ( Song et al, 2010 ). Plant behaviour is active, purpose-driven and intentional. In its capability for self-recognition and problem-solving, similarly to the other organisms described in this article, it is thus adaptive, intelligent and cognitive.

In 1902, Charles Minot stated in a speech to the American Association for the Advancement of Science, “A frank unbiased study of consciousness must convince every biologist that it is one of the fundamental phenomena of at least all animal life if not, as is quite possible, of all life. […] Consciousness is a device to regulate the actions of organisms to accomplish purposes which are useful to organisms and are thus teleological” ( Minot, 1902 ). More than a century later, Minot's insight that consciousness is ubiquitous for all life is finally coming to bear.


Single-celled organisms reproduce by first duplicating their DNA, and then dividing it equally as the cell prepares to divide to form two new cells. Multicellular organisms often produce specialized reproductive germline (reproductive) cells that will form new individuals. When reproduction occurs, DNA is passed from the organism to that organism’s offspring. DNA contains the instructions to produce all the physical traits for the organism. This means that because parents and offspring share DNA ensures that the offspring will belong to the same species and will have similar characteristics, such as size and shape.

Life: Defining the Beginning by the End

What defines the beginning of human life? This question has been the topic of considerable legal and social debate over the years since the Supreme Court’s Roe v. Wade decision&rdquodebate that has only been intensified by the recent controversies over human embryonic stem cells and human cloning. Answers to this question run the full gamut from those who argue that life begins at conception (the view of more than one major world religion) to those arguing that babies are not to be considered fully human until a month after birth (the position of Princeton Professor of Bioethics Peter Singer).

The range of dissent and disagreement on the question of when human life begins has led many to believe it cannot be reasonably resolved in a pluralistic society. Courts have ruled that the diversity of opinion on the topic precludes a judicial resolution, requiring instead that the matter be addressed in the political arena, where accommodation of divergent views can be wrought through debate and compromise. Many Americans appear equally unwilling to impose a single interpretation on society, preferring instead to allow decisions regarding the beginning of life to be largely a matter of personal choice.

While reluctance to impose a personal view on others is deeply ingrained in American society, one must question the legitimacy of such reluctance when the topic of our “imposition” is a matter (quite literally) of life and death. Few beyond the irrationally obdurate would maintain that human embryos are anything other than biologically Homo sapiens and alive, even at the earliest developmental stages. Equally few would contest the fact that, at early stages of embryonic development, human embryos bear little resemblance to anything we easily identify as “human.” For most people, reconciling these two facts involves the uncomfortably fuzzy process of drawing a line somewhere during the continuously changing process of human prenatal development and asserting: “There. That’s when human life begins&rdquoat least for me.” It is precisely the subjectivity and inaccuracy of this decision that fuels our discomfort at “imposing” it on others.

In contrast to the widespread disagreement over when human life begins, there is a broad social and legal consensus regarding when human life ends. Rarely has the point been made that the definition of human death can be applied to the question of when life commences with compelling symmetry. The definition of when life ends is both scientific and objective, and does not depend on personal belief or moral viewpoint. The current medical and legal understanding of death unambiguously defines both when human life ends and when it begins in a manner that is widely accepted and consistent with the legal and moral status of human beings at all stages of life.

Death is something most people readily recognize when they see it. People express very little confusion about the difference between a living person and a corpse. Surprisingly, however, the distinction is not as clear from a medical and scientific perspective. There is very little biologic difference between a living person in the instant before death and the body of that person an instant after death. Yet some property has clearly departed from the body in death, and that property is precisely the element that defines “human life.” What, then, is the difference between live persons and dead ones? How is death defined medically and scientifically?

The question of when and under precisely what conditions people are viewed as “dead” has itself been the subject of considerable debate. Traditionally, the medical profession considered a person dead when his heart stopped beating&rdquoa condition that rapidly results in the death of the cells of the body due to loss of blood flow. As the life-saving potential of organ transplants became increasingly apparent in the 1960s, the medical community undertook a reexamination of the medical standards for death. Waiting until the heart stops beating results in considerable damage to otherwise transplantable organs. After a long and contentious debate, a new standard of death was proposed in 1968 that defined “brain death” as the critical difference between living persons and corpses, a standard that is now widely (although not universally) accepted throughout the world.

Brain death occurs when there has been irreversible damage to the brain, resulting in a complete and permanent failure of brain function. Following the death of the brain, the person stops thinking, sensing, moving, breathing, or performing any other function, although many of the cells in the brain remain “alive” following loss of brain function. The heart can continue to beat spontaneously for some time following death of the brain (even hearts that have been entirely removed from the body will continue to beat for a surprisingly long period), but eventually the heart ceases to function due to loss of oxygen. The advantage of brain death as a legal and medical definition for the end of life is that the quality of organs for transplant can be maintained by maintaining artificial respiration. So long as oxygen is artificially supplied, the heart will continue to beat and the other organs of the body will be maintained in the same state they were prior to death of the brain.

Defining death as the irreversible loss of brain function remains for some a controversial decision. The fact that the cells and organs of the body can be maintained after the death of the individual is a disturbing concept. The feeling that corpses are being kept artificially “alive” as medical zombies for the convenient culture of transplantable organs can be quite discomforting, especially when the body in question is that of a loved one. Nonetheless, it is important to realize that this state of affairs is essentially no different from what occurs naturally following death by any means. On a cellular and molecular level, nothing changes in the instant of death. Immediately following death, most of the cells in the body are still alive, and for a time at least, they continue to function normally. Maintaining heartbeat and artificial respiration simply extends this period of time. Once the “plug is pulled,” and the corpse is left to its own devices, the cells and organs of the body undergo the same slow death by oxygen deprivation they would have experienced had medical science not intervened.

What has been lost at death is not merely the activity of the brain or the heart, but more importantly the ability of the body’s parts (organs and cells) to function together as an integrated whole. Failure of a critical organ results in the breakdown of the body’s overall coordinated activity, despite the continued normal function (or “life”) of other organs. Although cells of the brain are still alive following brain death, they cease to work together in a coordinated manner to function as a brain should. Because the brain is not directing the lungs to contract, the heart is deprived of oxygen and stops beating. Subsequently, all of the organs that are dependent on the heart for blood flow cease to function as well. The order of events can vary considerably (the heart can cease to function, resulting in death of the brain, for example), but the net effect is the same. Death occurs when the body ceases to act in a coordinated manner to support the continued healthy function of all bodily organs. Cellular life may continue for some time following the loss of integrated bodily function, but once the ability to act in a coordinated manner has been lost, “life” cannot be restored to a corpse&rdquono matter how “alive” the cells composing the body may yet be.

It is often asserted that the relevant feature of brain death is not the loss of integrated bodily function, but rather the loss of higher-order brain activities, including consciousness. However, this view does not reflect the current legal understanding of death. The inadequacy of equating death with the loss of cognitive function can be seen by considering the difference between brain death and “persistent vegetative state” or irreversible coma. Individuals who have entered a persistent vegetative state due to injury or disease have lost all higher brain functions and are incapable of consciousness. Nonetheless, integrated bodily function is maintained in these patients due to the continued activity of lower-order brain centers. Although such patients are clearly in a lamentable medical state, they are also clearly alive converting such patients into corpses requires some form of euthanasia.

Despite considerable pressure from the medical community to define persistent vegetative state as a type of brain death (a definition that would both expand the pool of organ donors and eliminate the high medical costs associated with maintaining people in this condition), the courts have repeatedly refused to support persistent vegetative state as a legal definition of death. People whose bodies continue to function in an integrated manner are legally and medically alive, despite their limited (or absent) mental function. Regardless of how one may view the desirability of maintaining patients in a persistent vegetative state (this being an entirely distinct moral and legal question), there is unanimous agreement that such patients are not yet corpses. Even those who advocate the withdrawal of food and water from patients in persistent vegetative state couch their position in terms of the “right to die,” fully acknowledging that such patients are indeed “alive.” While the issues surrounding persistent vegetative state are both myriad and complex, the import of this condition for understanding the relationship between mental function and death is clear: the loss of integrated bodily function, not the loss of higher mental ability, is the defining legal characteristic of death.

What does the nature of death tell us about the nature of human life? The medical and legal definition of death draws a clear distinction between living cells and living organisms. Organisms are living beings composed of parts that have separate but mutually dependent functions. While organisms are made of living cells, living cells themselves do not necessarily constitute an organism. The critical difference between a collection of cells and a living organism is the ability of an organism to act in a coordinated manner for the continued health and maintenance of the body as a whole. It is precisely this ability that breaks down at the moment of death, however death might occur. Dead bodies may have plenty of live cells, but their cells no longer function together in a coordinated manner. We can take living organs and cells from dead people for transplant to patients without a breach of ethics precisely because corpses are no longer living human beings. Human life is defined by the ability to function as an integrated whole&rdquonot by the mere presence of living human cells.

What does the nature of death tell us about the beginning of human life? From the earliest stages of development, human embryos clearly function as organisms. Embryos are not merely collections of human cells, but living creatures with all the properties that define any organism as distinct from a group of cells embryos are capable of growing, maturing, maintaining a physiologic balance between various organ systems, adapting to changing circumstances, and repairing injury. Mere groups of human cells do nothing like this under any circumstances. The embryo generates and organizes distinct tissues that function in a coordinated manner to maintain the continued growth and health of the developing body. Even within the fertilized egg itself there are distinct “parts” that must work together&rdquospecialized regions of cytoplasm that will give rise to unique derivatives once the fertilized egg divides into separate cells. Embryos are in full possession of the very characteristic that distinguishes a living human being from a dead one: the ability of all cells in the body to function together as an organism, with all parts acting in an integrated manner for the continued life and health of the body as a whole.

Linking human status to the nature of developing embryos is neither subjective nor open to personal opinion. Human embryos are living human beings precisely because they possess the single defining feature of human life that is lost in the moment of death&rdquothe ability to function as a coordinated organism rather than merely as a group of living human cells.

What are the advantages of defining the beginning of human life in the same manner that we define its end, based on the integrated organismal function of human beings? To address this question, the alternative arguments regarding when life begins must be briefly considered. While at first inspection, there appear to be many divergent opinions regarding when human life commences, the common arguments are only of three general types: arguments from form, arguments from ability, and arguments from preference. The subjective and arbitrary nature of these arguments stands in stark contrast to the objective and unambiguous definition that organismal function provides for both the beginning and end of human life.

Of all the arguments regarding when human life begins, the most basic, and perhaps most intuitive, is that to be human, one must look human. Early human embryos are often described as “merely a ball of cells,” and for many, it is difficult to imagine that something that looks more like a bag of marbles than a baby could possibly be a human being. Fundamentally, this argument asserts that human life is worthy of respect depending on appearance. When plainly stated, this conclusion is quite disturbing and also quite problematic. What level of malformation are we willing to accept before we revoke the right to continued existence? How are we to view children whose mature form will not be completely manifest until puberty? Form alone is a profoundly trivial and capricious basis for assigning human worth, and one that cannot be applied without considerable and obvious injustice.

The superficiality of equating worth with form is sufficient for most to reject this argument and retreat to a functional definition: form per se is not the issue rather, it is the ability to function as a human being that defines the beginning of human life. Human beings are capable of a number of distinctive functions (self-awareness, reason, language, and so forth) that are acquired gradually over prenatal life as development proceeds. Therefore, the argument goes, human worth is also gradually acquired, with early embryos being less human than more developed fetuses.

A number of seemingly independent arguments regarding when life begins are in fact variations on this argument from ability. Thus, the proposal that human life begins when the fetus becomes “viable,” or capable of surviving outside of the womb, is a subset of the ability argument that gives conclusive weight to the suite of abilities required for survival independent of the mother. Similarly, the common argument that embryos are human when they are in the womb of the mother (where they can develop into babies), while embryos generated in the laboratory are not, is also a variation on the ability argument that equates developmental ability with human life and worth.

While the argument from ability is less superficial than the argument from form alone, it is no less problematic. As noted above, functional definitions have been repeatedly rejected as a legal basis for the definition of death, in part due to their arbitrary nature. One can certainly identify any number of elderly and disabled people who are less functionally adept than newborn infants&rdquoand perhaps even late-term fetuses. While Western culture has a strong tradition of meritocracy, providing greater economic and social rewards to those who demonstrate greater achievement, basic human rights are not meted out according to performance. Unless we are willing to assign “personhood” proportionate to ability (young children, for example, might be only 20 percent human, while people with myopia 95 percent), the limited abilities of prenatal humans are irrelevant to their status as human beings.

The final and perhaps the most emotionally compelling argument for assigning human status to a developing embryo is the extent to which parents desire a child. Yet the argument from being wanted, which equates status as a human being with the desire of a second party who has the power to confer or deny that status, essentially reduces the definition of a human being to a matter of preference. You are human because I choose to view you that way. The fact that human status can be positively conferred for “wanted” embryos as well as denied for the “unwanted” illustrates the fundamental arbitrariness of this argument. The preferences of individuals who possess the power to impose them on others are hardly a compelling basis for legislation on human life.

Despite the apparent diversity of views regarding when human life begins, the common arguments thus reduce to three general classes (form, ability, and preference), all of which are highly subjective and impossible to reconcile with our current legal and moral view of postnatal human worth. It is, in fact, the subjectivity and inconsistency of these views, rather than their diversity, that makes them so unsatisfying as a basis for legislation on human life.

Unlike other definitions, understanding human life to be an intrinsic property of human organisms does not require subjective judgments regarding “quality of life” or relative worth. A definition based on the organismal nature of human beings acknowledges that individuals with differing appearance, ability, and “desirability” are, nonetheless, equally human. It is precisely the objective nature of such a definition (compared to vague “quality of life” assessments) that has made organismal function so compelling a basis for the legal definition of death.

Once the nature of human beings as organisms has been abandoned as the basis for assigning legal personhood, it is difficult to propose an alternative definition that could not be used to deny humanity to virtually anyone. Arguments that deny human status to embryos based on form, ability, or choice can be readily turned against adult humans who have imperfect form, limited ability, or who simply constitute an inconvenience to more powerful individuals or groups. Indeed, such arguments can be quite protean in their ability to deny rights to anyone not meeting an arbitrary criterion for humanity. Abraham Lincoln made this very point regarding arguments based on form, ability, and choice that were put forth in his day to justify the institution of slavery:

It is color, then the lighter having the right to enslave the darker? Take care. By this rule, you are to be slave to the first man you meet with a fairer skin than your own.

You do not mean color exactly? You mean the whites are intellectually the superiors of the blacks, and, therefore, have the right to enslave them? Take care again. By this rule, you are to be slave to the first man you meet with an intellect superior to your own.

But, say you, it is a question of interest and, if you can make it your interest, you have the right to enslave another. Very well. And if he can make it his interest, he has the right to enslave you.

Postnatal humans run very little risk that embryos will someday organize politically to impose restrictions on the rights of “the born.” However, once society has accepted a particular justification for denying rights to one class of individuals, the same justification can readily be applied to other classes by appealing to the simple argument: “Society has already determined that form, ability, or preference defines human life and thereby restricts human rights. Why should the same standard not be applied in this case?” In American society and jurisprudence, arguments from accepted precedent carry great emotional and legal force. Society must determine whether it is willing to accept the current subjective and arbitrary basis for determining the status of prenatal human beings as a legitimate precedent for future legislation on human rights.

Embryos are genetically unique human organisms, fully possessing the integrated biologic function that defines human life at all stages of development, continuing throughout adulthood until death. The ability to act as an integrated whole is the only function that departs from our bodies in the moment of death, and is therefore the defining characteristic of “human life.” This definition does not depend on religious belief or subjective judgment. From the landmark case of Karen Ann Quinlan (1976) on, the courts have consistently upheld organismal function as the legal definition of human life. Failure to apply the same standard that so clearly defines the end of human life to its beginning is both inconsistent and unwarranted.

The conclusion that human life is defined by integrated (organismal) function has wide-reaching implications, both political and moral. While the public domain has limited authority to promote morality, it does have both the power and the responsibility to prevent harm to individuals. A consistent definition of what constitutes human life, both at its beginning and at its end, requires that current legislation dealing with prenatal human life be considered in light of both biological fact and accepted legal precedent regarding the definition of human life. If current legislation enables and supports the killing of human beings based on a scientifically flawed understanding of human life, laws can and should be revised. Clearly, such a revision would not be without political cost. Yet allowing life-or-death decisions to be based on arbitrary or capricious definitions is also a course of action that is not without considerable social and moral cost.

Dr. Maureen L. Condic is an Assistant Professor of Neurobiology and Anatomy at the University of Utah, currently conducting research on the regeneration of embryonic and adult neurons following spinal cord injury.