What is Life? What is A Life?

This is an enhanced version of a talk that I gave to the Philosophy Forum in Melbourne, Australia on 04 December 2016


What is a life? What is life? What does “alive” mean?

Is life sacred? What kinds of life are sacred? What makes them sacred? What does “sacred” mean?

Heated ethical arguments about such issues can arise when some kinds of research or practices or legislation are contemplated. The answer given to the question depends on the answerer’s beliefs about the fundamental nature of life.


Life is thought of as the property or quality that distinguishes living organisms from dead organisms and other inanimate matter. But this simple description omits to say how to make the distinction. Some life forms seem inanimate at first sight, for example spores or slime. And continued argument about how to decide exactly when human death occurs, with such concepts as brain death replacing earlier concepts such as cessation of heartbeat or breathing, shows that the criteria for being alive are uncertain.

A common biological definition is that life implies four functions:

  • metabolism – using material and energy within their body to support continued functioning;
  • reproduction – producing, from within the bodies of living parents, new separate organisms that become similar to their parents;
  • growth – increasing in size from infant to adult;
  • interaction with the environment – taking action as needed for metabolism, growth, reproduction and safety.

(On the matter of reproduction, most individual mammals are unable to reproduce alone, and there are sterile individuals in all sexually-reproductive species, but we would still say they are alive. This definition is just one illustration of the ambiguous concepts relating to life.)


Other definitions require also that living beings move, communicate, evolve, keep their internal environment stable, have feelings, be intelligent and/or be (sometimes) conscious. I think such additional characteristics might apply to all or most species of life on Earth, bur I would not regard all of them to be necessary. Some people would require living organisms to function using chemical reactions, so as to exclude manufactured devices.

A definition that invoked the science of thermodynamics first appeared in the book What is Life written by the famous quantum theorist Erwin Schrödinger. He said that living beings are “the class of phenomena that are open or continuous systems able to decrease their internal entropy at the expense of substances or free energy taken in from the environment and subsequently rejected in a degraded form.”

This means that a living thing takes in food and energy. Its body uses the energy for operating its physical and mental processes, and it uses the material to build or replace the cells that it is composed of. It then discards what is left over. This definition does not specifically address growth or reproduction.  But if life is to persist indefinitely, it must reproduce, and/or add new parts to itself to replace any damage, and/or be able to sustain is bodily parts against damage and shortage of food and energy.

Schrödinger’s concept is applied in the search for signs of life in other parts of the universe, where the by-products of life are probably the only signs that could be detectable from Earth. Scientists look at distant planets to see if there is evidence of chemicals that would normally react together. If at least one such chemical would normally have disappeared but is found to be still there, then it is assumed that its presence is the result of some living organism continuing to produce it. This does not constrain life to being dependent on specific chemicals, such as carbon or water in its liquid state, which are essential basic components of all life on Earth. We might speculate about chemicals such ammonia and methane, which are gases under conditions on the surface of Earth, but are liquids in colder parts of the solar system and beyond. But the physics and chemistry under such conditions would compel any life forms to be very different from life as we know it.

(Scientists actually have another way of searching for extraterrestrial life. They look for signs of “intelligent life” that might be using radio and other electromagnetic radiation for communication and other purposes. Such signals would have patterns that would be unlike the radiation given off by stars and other cosmic objects. [I will discuss later why I think all life forms must be intelligent.] Only one species of life on Earth constructs and uses devices that emit substantial amounts of electromagnetic radiation, and it has done so for only a very short period of time. So this type of searching would miss any extraterrestrial life that did not emit a lot of structured radiation. In any case, there has as yet been no detected sign of artificial radiation after decades of searching.)


Whatever the definitive characteristics may be, if life must entail performing at least some of the four basic functions, then it must depend on a structural system that can continue performing them. That is, life depends on a sustainable arrangement of interworking parts. For every form of life, its parts and their interactions must be able to operate in the conditions of its environment, such as the temperature, the pressure, the winds and the presence or absence of particular chemicals. Otherwise the system will fail and that piece of life will die.


This applies no matter how simple or complex this piece of life happens to be.


Some people think certain types of things are alive that other people think are not. Bacteria, fungi and plants are always included as life forms. Things, such as fire, machines, virtual life and viruses, all of which can have some lifelike characteristics, are commonly excluded.

Viruses have no metabolism: they neither take in nourishment nor grow. They do not reproduce, but may be replicated whenever their DNA or RNA gets into cells of living organisms. However, they are given identification by the use of taxonomic names in the same way as living organisms. They can be mutated and evolved into new strains, and hence they appear to act as if they are alive

Because of these characteristics, viruses are treated in a similar way to living organisms in the practice of medicine (taking due regard of the different characteristics of organisms and viruses). The term “live virus” is used to distinguish an intact virus from one that is unable to be virulent, for example for use in a vaccine. Viruses do not have a lifespan: they will continue indefinitely until some external agency damages them or until they deposit their genetic material into the cell of an organism.

Fire, machines and virtual life do not have a metabolism or a life cycle or take action to reproduce, find food or avoid danger. Virtual life may be programmed to appear to do these things but it doesn’t actually perform any of them. It is just a depiction of them.


So far, all the discussion about life has referred to its physical characteristics and processes. It implies that life is nothing more than a physical process. Most scientists and many other people believe that is all it is. They would regard it to be purely the result of phenomena that started from arrangements of inanimate matter, and diversified through many stages of evolution to produce the diversity of life forms that now exists.

But there is no accepted scientific theory of how living organisms first came to exist: Darwin’s theory of evolution addresses only how there came to be many different life forms.


It is generally thought that any process of life emerging from matter would have begun with particular chemicals being able to generate copies of themselves, a process known as self-replication.

Some types of self-replicating chemicals occur in nature and others have been manufactured. Scientists have been using them in trying to produce new living organisms. (This is not the same as putting DNA – either modified from another organism or artificially generated – into a living organism.) But if they were to succeed, this would not be a re-enactment of how life would have originally emerged from inanimate matter but a process of intentional creation – but not by the creator envisaged by creationists. It might, however, demonstrate the feasibility of the evolutionary concept.


Biologists and other scientists have identified a lot of things that they think would need to happen for life to be able to emerge from inanimate matter. They have shown how some of the required chemicals, including strings of RNA, could have occurred “naturally”. They have shown how membranes could be formed that might wrap around the RNA and other necessary material to create an organism. But for the RNA to be able to recreate itself plus all the other materials, and assemble them so they formed the first living organism would require a very unlikely series of coincidences.

But even this would not have been enough.

In addition to the things specified in the description of life, organisms need to be intelligent in various ways. They need to be able to recognise the aspects of their environment that are relevant to their needs of metabolism, growth, reproduction and safety. They also need the ability to perform the appropriate actions for each of these. And they also need some compulsion to respond to their needs at the appropriate time and to the appropriate degree. For example, they must know what to eat, what not to eat, when to eat and how much. They may need to be compelled to look for food if no food is readily available. However, the ability of some organisms to look for food is very limited, and all organisms can make mistakes in their recognition of food or danger.


All this amounts to a very complex set of requirements including some very delicately balanced regulatory processes. The probability of all these things coming together is a bit like “a whirlwind in a junkyard assembling a Boeing 727”, which is how the physicist Fred Hoyle inappropriately described the concept of evolution. (Later in this essay I will explain why applying this comparison to evolution was inappropriate.) We might think that it was just an extraordinary coincidence that allowed such a precise and complex an arrangement of different kinds of material to occur by chance through the physical processes of the early stages of planet Earth.

But many scientists are confident that life would “automatically” emerge wherever in the universe there happened to be liquid water. If this is likely, might something else, something supernatural perhaps, always be available to guide the assembly of the life forms and make them come alive? Many people believe that there must be a “life force” or a supernatural element to produce and/or sustain life.

There is no evidence of a physical life force, but some people, including a few scientists, think that the universe is in some way alive, or that all matter is alive, and this gets over the problem of how the first life could have occurred.

For the universe to be alive as a complete entity it would, presumably, display the four requirements of life:  metabolism, reproduction, growth, and interaction with its environment. Perhaps a case could be made for the large scale cosmic processes being like a metabolism. Then the multiverse, if it is real, would embody reproduction, and the continuing expansion of space would be equivalent to growth. And there would need to be a bountiful environment surrounding the universe to supply the matter and energy for the universe’s metabolism and growth and to receive the discarded residue.

With such a picture, the complex organisms in this living universe might be equated with the microorganisms that inhabit most multicellular organisms on Earth. This calls to mind the verse, attributed to Jonathan Swift:

So naturalists observe, a flea
Has lesser fleas that on it prey,
And these have lesser fleas to bite ‘em,
And so proceed ad infinitum.

However, if the universe were a living entity, that would not explain what makes the difference between inanimate matter and live organisms.

Regarding the suggestion that all matter is intrinsically alive, there is no counterpart to any of the four requirements of life – except, perhaps for growth – in a lump of metal or rock or any other object.

So neither of these two ideas deals with how a particular arrangement of matter could have occurred to deliver all the functional requirements for the original life form on Earth. They give even less promise than the attempts to explain how such an arrangement could arise through physical processes.


Until there is a complete and satisfactory explanation of how a physical process could produce some primordial living organism, or there is a strong indication that some element that is intrinsically different from all material processes could be the agent and arrenger of life, I will have to regard the issue of the origin of life to be not yet resolved.

Perhaps some scientists might think that the construction of a replica of a live organism using only inanimate materials would resolve the issue in favour of life arising from a purely physical process. But I wonder if the finished product would be a living or a dead organism. If it were to be alive, two issues arise; at what stage of construction would it have become alive, and might some life force – physical or supernatural – have been waiting to “switch it on” once its structure had become viable? And I think the process of constructing such a replica would be an excruciatingly difficult task. It would not necessarily demonstrate that any life form could occur without artificial help, but there would need to be good evidence to claim that such any agent of help actually existed.



Is Life Sacred?

One matter that arises from the idea that life has some supernatural connection is whether life is sacred. The concept of sacredness, or sanctity, can have both secular and religious connotations. From a secular perspective it can mean great importance, value or inviolability. Some highly valuable objects, such as certain paintings like the Mona Lisa or historical records like the original Magna Carta, might be regarded as sacred.

From a religious perspective sacredness can additionally mean holiness, saintliness, or godliness.

So the issue of whether life is sacred has two points of view. Beginning with the secular concept, we might distinguish between living matter and living organisms. Living matter would include body parts that are being artificially preserved remotely from the body they came from, and such things as spermatozoa. In particular cases, body parts can be important, such as for use as vital transplants, but this would not be enough to make them sacred.

The various species of living organisms might be judged to each have different degrees of value, at least by humans, who would value them according to their usefulness or beauty, and by their adverse affects or perceived ugliness. Or they might be judged from an altruistic or compassionate point of view, particularly if they are acknowledged to feel pain or distress. But since different people have different values and preferences, decisions about what organisms – and other things – are sacred will depend on who is making the judgment.

From their own point of view, most species, if not all, have built-in urges to avoid or minimise harm. Whether this makes them regard life, or their life, to be sacred would depend on their capability of thinking about such concepts and on any beliefs they might have. For most humans, their own life is very precious, but there are conditions under which their life can feel so intolerable that they passionately want to dispose of it. So there will be differences of opinion about what actions would violate the sanctity of life.


From a religious perspective, the sacredness of living organisms depends also on what their relationship is to some supernatural entity. For example, the lives of humans may be considered to be sacred if humans have souls, and certain other species may be considered to be not sacred on the assumption that they do not have souls. The issue then is deciding which species qualify as having souls and at which stage of their life cycle they acquire their souls. Any judgment on this would depend on religious criteria. Such criteria depend on the particular tenets of each religion. There is inconsistency between religions on this, and on what treatment is appropriate for the lives of different classes of people.

These different viewpoints lead to controversy regarding the morality of virtually everything related to life.



Irrespective of how it might have come into existence, primordial life would have emerged in an environment very different from our present environment, and it would have been very different from any of the forms of life that we are familiar with, including bacteria. So how did the more complex organisms, like us, occur?


Development of Life on Earth

How did the diversity of life happen? Once the first life form came into existence it would have had to rely on its environment continuing to be benign and to support its functions, otherwise it would not have been able to survive and reproduce. And reproduction has always been essential if life were to continue and not die out. But the reproduction process does not usually produce precise copies of the parents. This means that there will be more and more variations between the individual organisms in the succeeding generations as the differences are passed on and further differences are added. Some such differences would have been innocuous, some would have been fatal and a tiny few would have given some kind of advantage.

At the same time, the environment would have needed to continue being supportive enough for all this to happen. It is easy to conclude that it was a miracle that it did. But the environment is not uniform, and different organisms would be more suited to different parts of the environment. Those unsuited to their environment would die out, and those more suited would flourish. This is the basis of the evolutionary explanation of how life on Earth came to be so diverse in form and function. However, it is not the only explanation.

The supernatural explanation that gets around the issue of how life began also gets around the issue of how all the diverse life forms came to exist. It says that the various life forms were each designed and created in their present shape during some act of specific intelligent creation.

I think the evidence for intelligent creation is, at best, extremely small. There is overwhelming evidence of an evolutionary process continually producing diversity of life through a process whereby offspring are slightly different from their parents, and some of these differences are passed on to the following generations. And we can see this process still occurring.

So once there was some primordial form of life with the capability and opportunity of sustaining itself, and reproducing, and producing changes in its offspring, the processes of nature would have been able to continually develop and diversify its progeny into the multitudinous forms that we now recognise. There is abundant biological and geological evidence of this. (Chapter 7 of Agnosticism: The Third Perspective on this website explains this in more detail.)


Geological evidence points to some form of life existing at least 2.7 billion and possibly 3.8 billion years ago. The first living entity on Earth would probably have consisted of something like a microscopic film enclosing the RNA or DNA that would have controlled its functioning and reproduction. It would have gradually diversified into multitudinous forms of archaea and bacteria that proliferated and occupied many parts of the earth’s surface. Evidence also points to the appearance, one or two billion years later, of eukaryotes, i.e., organisms with their genetic material enclosed in a nucleus. (The earlier organisms, bacteria and archaea, are known as prokaryotes) There are no multicellular prokaryotes, but there are signs of multicellular eukaryotes at about 700 million years ago. These developed into increasingly complex organisms – animals, plants, fungi and a variety of other groups of organisms.

In simpler types of single-cell organisms, reproduction consists in the cell growing and then splitting into two or more cells that are like smaller versions of the cell that split. This is referred to as cell division. Cells resulting from the division are occasionally slightly different from the parent cell and have slightly different genetic material, which can lead to the development of new species.

Cell division also occurs within most of the cells of multicellular organisms – in fact this is the main process in the growth of these organisms. During these organisms’ lives, cells are continually dying and being replaced by the division of other similar cells.

In the most common type of reproduction by division, each “daughter” cell is a half of the parent. Some kinds of bacteria produce one or more daughter cells that are much smaller versions of the parent but are still fully functional.


Unity of Life

Each succeeding generation is, in a sense, just a continuation of its predecessor. All individual organisms have arisen from having been parts of previously existing organisms. So there is an intrinsic unity between all forms of life on earth. The processes of metabolism, reproduction, mutation, separation and combination of all known life forms are all controlled by DNA and/or RNA.

Many types of microorganism readily exchange segments of their DNA, often incidentally giving recipients new abilities or features. A consequence of this is that in all species each individual member will be different in some way from all of the other members. Differences between individuals also occur because the genomes of offspring are almost always different from the genomes of parents as a result of mutations and sexual reproduction.

In genetic engineering, segments of DNA are deliberately transferred from one species to another – often very remotely related – species to provide the recipient with some specific additional characteristic. There is evidence that cross-fertilisation continually occurs between eukaryotes (including us) and prokaryotes and viruses, with the progeny acquiring characteristics of both “parent” species, and passing them on to further generations. An interesting example is a species of snail that is green. It has acquired plant genes to produce chlorophyll. The snails turn red in autumn.


Almost all eukaryotes have other types of organisms living on and/or within their bodies, some providing essential processes for the hosts, some disruptive, and some parasitic. There are about ten times as many “non-human” microorganisms in and on a human body as there are cells of the body itself. (But the host cells are very much larger than the resident organisms, and they comprise most of the total body mass.) Some of these microorganisms can alter the mood or the thinking or the functioning or the health of the person they inhabit.

Evidence suggests that eukaryotes arose as a result of a single-cell bacterium becoming functionally incorporated into the body of a single-cell archaon, with the nucleus and mitochondria of each subsequent eukaryotic cell being descendents of the incorporated bacteria.


In contrast to reproduction by cell division, sexual reproduction is the fusing of specific parts of two biologically compatible but distinguishable organisms – the egg and the sperm or equivalents to them – usually of the same species.

However, the concept of species, in fact the concept of classifying all life into domains, kingdoms and so on down to genera and species, while very useful, does not mean that life is rigidly divided into these categories. There are many cases where the distinctions are not clearly definable. The transferability of genetic material between different kinds of organisms explains why.


Most biologists think that all existing life on Earth must have descended from the same common ancestor. But there is an argument that there is no single common ancestor of life, and that archaea and bacteria evolved separately. This is based on the fact that archaea and bacteria have different kinds of outer coatings. However, their coatings are not very different: they are mainly composed of similar materials, glycol-ester-lipids for bacteria and glycol-ether-lipids for archaea.

This may be compared with the kingdom Animalia, one of the three major groupings of eukaryotes. Looking at just three kinds of animals, mammals, insects and crustaceans, it is easy to see their different kinds of body coatings. All eukaryotes probably have a common ancestor in the speculated archaeon that synthetised with a bacterium to create a new kind of organism; and the coatings of the members of the kingdoms of animals, of plants and of fungi, are also different from each other. Archaea and bacteria have many features in common. There is no reason to assume they emerged independently. And there is no known evidence of any other kind of life having arisen on Earth.

So it seems that all life on Earth has been one biological unity since the very first life form came into existence. From this point of view, there are new arrangements of living matter but no new beginnings of life.

But the reality is not so simple.


Individual Identity

Notwithstanding this biological unity, there is a distinction between life and a life. Organisms can be seen to be spatially separate from each other, distinctly recognisable from each other, independently capable, and differently intelligent and emotional. They are individual lives that come into being and die.

But what exactly is an individual life and when does it begin? Is a full-grown cell the same entity that it was when it just started to grow? Is it still the same entity after it has split into two? Most people would probably agree that a single cell organism is one entity before it splits, but two new separate entities afterwards, able to go their separate ways. So for single cell organisms that reproduce by division, life as an organism begins (and ends) at the moment of splitting.

Multicellular organisms usually do not reproduce by splitting into similar parts. Most complex multicellular organisms reproduce through the sexual process – the uniting of two dissimilar cells, a sperm and an egg. This seems to be a reverse process to cell division, but the new cell is significantly different from either of the cells it was formed from.

The process by which eukaryotes reproduce from fertilised female cells differs across the range of species. Plants grow from seeds that have to depend on being in a suitable location and supplied with water. Many species, such as plants and some fish, produce sperm and eggs that are fertilised when external agents bring them together outside the bodies of the parents. Many other species produce eggs that are fertilised inside the mother and hatch outside the body of the mother. The time of the beginning of the life of individual members of these species would probably be arbitrarily assigned to the time that they start to emerge from their birth shell. And in the case of placental mammals, the egg is usually fertilised inside the mother’s body and develops there until it is born. The exceptions are when the egg is artificially fertilised and then artificially implanted in the body of the birth mother.


Parts taken from the bodies of some plants and animals can be grown to become separate mature organisms. New plants can be grown from cuttings or from the culture of individual cells, and can co-exist with the parent plant in some remote location. Small parts from some animals, for example planarian worms and some jellyfish that have been put through a blender, can regenerate into complete organisms provided that they contain some of each type of the animal’s tissues. These are all cases of reproduction, irrespective of whether the separation of the parts occurs naturally or is produced artificially. So, a cutting that is taken from a plant put into a pot of soil and grows becomes, at some point, a separate living organism. (If the cutting is just left unattended and dies, what is the entity that dies, and at what point of time does this happen?)


Multicellular organisms can be thought of as associations of cells whose interactions make the unit a new living entity. But there are degrees of coherence in these associations. For example, slime moulds are types of single-cell organisms that normally hunt as a herd, feeding on other microorganisms. Under stressful conditions the individual slime microbes form coherent associations looking and acting like slugs or fungi, with differentiated body parts. When these associations look like slugs, they also move and behave a bit like slugs. Under dire conditions some individual members may become spores that will awaken and produce new colonies when conditions improve, while many of the other members die.

These and other types of associations – such as corals, which are polyps that are symbiotic with algae – are loosely held together, and the members are still separate organisms.

Some loose associations may cease to exist without any of the members dying, as when a stressed slime mould structure disassembles upon conditions becoming favourable. In more complex associations, the members form differentiated groups, i.e., organs, that depend on each other for survival. Failure of an organ such as the heart or liver can cause the whole association, i.e., the body, to die. The more strongly they depend on each other, the greater the likelihood that all cells will die if the association ceases to exist. Very complex (multicellular) organisms, including humans, are strongly interdependent associations, and usually all cells die from lack of support when the organism dies. But as mentioned earlier, it is possible for individual cells to be artificially kept alive, to divide and grow. Also, the association itself can survive if it loses larger parts that are useful but not essential, in animals for example, a leg or an eye.


From now on the discussion will concentrate on multicellular organisms, and in particular mammals.

Sperm and eggs are detachable parts of organisms. They do not have the functionality that allows them to exist as organisms, and the composite newly-fertilised egg cell, which is the union of sperm cell and a compatible egg, also lacks these functions. New organisms develop by the action of single-cell eggs continually dividing into more and more cells which remain coherently associated but become differentiated into specialised organs. Their functioning as organised units develops incrementally. At some stage the association becomes the life of the new multicellular organism, superseding the separate lives of its members.

So, while the life of a new, single cell, prokaryote may be said to begin with the division of its parent cell, different criteria are needed to identify the beginnings of mammalian lives.

The philosopher Peter Singer suggested it would be humane to euthanise babies that were born with disabilities that would make their lives so miserable as to greatly outweigh any pleasure that they might experience. He acknowledged that, at some later stage, euthanising them would be regarded as murder. In his view, their life as persons should be considered to begin when they were 30 days old. This choice of 30 days seems to be quite arbitrary. Some people would put the beginning at some time before birth. How could any such date be justified?


What Identifies the Beginning of an Individual Mammalian Life?

Biological Criteria

From a biological point of view, some possible criteria for identifying the beginning of a multicellular mammalian life are:

  • separation;
  • independence;
  • activity;
  • stage of development.

It would be consistent for these criteria to be applied equally to all species of organism.



In this context, separation means that the new life has become physically separated from, or is not a part of, any other organism. The obvious example is a baby at or soon after birth. This may suggest that a baby that is removed from the womb by caesarean section before its full term begins its life earlier than it would have if it had been allowed to proceed to natural birth. (Its official birth date implies this.)

There could be argument about how separate an unborn foetus or a new-born baby is. What is the significance of the umbilical cord? Does the baby become separate only when the cord is cut after it has been born?

And conjoint twins are not separate but are separately alive and have individual minds and lives.

But being separate does not necessarily mean that something is, or is yet, a new life. A kidney removed for transplanting is not a life, even though it is alive. Its only function is that of filtration, and it is able to do that only as part of a living body. This could be contrasted with a cutting from a plant.

So, while being separate might usually be a requirement for identifying individuality, it does not seem to be sufficient.



No form of life is completely independent: all are dependent on their environment for food and energy, and often for cooperative assistance. But there is a difference between passive dependence. An example of passive independence is where all the action to sustain life is taken by the environment, as with an embryo or foetus which is completely supported by its mother. An equivalent example of “active dependence” is where the organism takes action to provide for its own food and safety. We usually regard such active dependence as independence. But there are different stages of how much action a developing body takes, and how much the environment, including other organisms, actively gives. So if independence is to be a criterion for the beginning of a life, the decision of when it is sufficiently independent must be arbitrary. It might, for example, be claimed that the beginning of its life is when it has independently developed certain capabilities, such as an animal when it has been weaned and can forage. So this could be some time after birth.

(We are never independent of the trillions of microorganisms that reside within our bodies, but I do not think this is relevant to this particular criterion.)



Activity comprises self-generated motion of all or part of the organism or its interior processing. Seeds and spores are quite inactive and presumably have not yet begun their lives before they begin to germinate. But apparent inactivity does not necessarily mean absence of a life. A few years ago a bacterium that had been locked beneath a Greenland ice sheet for more than 120,000 years was revived by scientists at Pennsylvania State University. After being placed in a nutritious environment it began producing fresh colonies. When discovered it had been under three kilometres of ice. So life can be in a condition of inactivity – or “suspended animation” – for a long time. Another example of suspended animation is the seed of a plant, which may be kept alive for at least hundreds of years before being put into a suitable medium and then beginning to sprout. These particular cases have little or nothing to do with the beginning of mammalian life. However, they might suggest that if life begins at the moment of fertilisation, as some people think, it could be inactive for a very long time. But it may or may not be a life during this time. Perhaps the bacterium already had a life before it was imprisoned by the ice, and the life of the seed might not have begun until it was planted.


During pregnancy there comes a time when a foetus starts to move in the womb, initially without its movements being detectable by its mother. Perhaps its life could be considered to begin when it first moves parts of its body or limbs. It would be difficult to determine when this occurred for each individual foetus, and the earlier movements would be involuntary. Although some arbitrary date could be chosen, based on average times after conception, this criterion of activity does not seem to be a very useful criterion.


Stage of Development

Stage of development could refer to the creation of processes such as heartbeat or the appearance of a brain. Or it could refer to the progressive acquisition of new faculties and capabilities such as mobility, intelligence and consciousness.

But what is the significance of a pulsating heart? A heart, which is essentially a pump, can continue beating when it is removed from the body, and an artificial heart can produce a constant flow of blood instead of a pulsating one. But a heart does not itself signify an individual life. Also, the existence of a rudimentary brain does not in itself necessarily confirm the beginning of a new life. But some stage in the development of its functions might.


To survive, all organisms must be able to distinguish between what is food and what is not, and whether an environment is safe and favourable or not. Survival also requires knowing how to respond in each type of event that it encounters. Organisms we would regard as extremely simple or primitive have a range of faculties in a form sufficient for their needs. For example, the gut bacterium Escherichia coli (which we all have living inside us) has more than thirty different systems for sensing such things as oxygen, light, pressure, kinds of food, and what other species of organisms are nearby, and it also has the ability to act in accordance with what it detects. And it has short-term and long-term memory. Having such faculties, at any degree of complexity or sophistication, signifies intelligence. But this is an organism that reproduces by cell division. The bacterium builds a replica of itself inside its body, and when the replica is completed the junction between it and the “parent” part of the cell and both parts are now separate fully-functional organisms.

But most animals, including humans, gain their corresponding faculties bit by bit. The bodily structure is not completed until adulthood and the brain structure is not regarded to be mature until some years later. But no one would accept that we must wait for all this to happen before saying that this individual life has just begun when it had been doing very many things by itself for years. Some arbitrary criterion, such as a specific degree of intelligence, might be chosen as the beginning of life. But there still needs to be a justification for the decision.

Could the beginning of consciousness be the deciding stage? Consciousness can be distinguished from intelligence, with things like computers being intelligent but not conscious. Consciousness often but not necessarily includes the ability to feel pain and emotions. And, just as there can be types and grades of intelligence, there seem to be types and grades of consciousness. And this relates to the issue of when a mind begins. But a large part of the intelligence of a brain relates to things other than consciousness. There is no sure way of detecting when a developing brain begins to produce consciousness as distinct from having unconscious reactions.

There is evidence that unborn babies can hear what is happening outside the womb, and that they can react to hearing some of these things after birth. A typical example is a song or other music that the baby heard several times before birth, and responded to on hearing it again after it was born, but did not respond to similar unfamiliar sounds. This might be evidence of consciousness in the womb. But there is also evidence that the unconscious mind can “know” things that the conscious mind does not know at the time but can “remember” later. As an example, we are usually not conscious of everything that our eyes see when looking at something, but later, on prompting, can often say where in the scene a previously “unseen” object was. This does not disprove that an unborn baby would be conscious, but it places some doubt on the matter.

Babies are often born significantly earlier than the expected gestation time of about nine months. This can occur spontaneously because of an illness of the mother, by some accident, or by the action of a medical practitioner. Given appropriate care, these babies are mostly able to survive and develop into normal adults. Such cases include babies born as early as 23 weeks after conception. The survival rate is much lower with the earlier births, but there are potential hazards with all births. This might suggest that a human life begins somewhere between about 23 weeks and birth. In societies where abortion is legal there is usually a period of gestation after which abortion becomes illegal. Perhaps this is an implicit assumption regarding the time when a life begins.


Alternatively, could a new human life be considered to be established when it is equivalent to the intelligence or capability of an adult member of some other species, or of a particular computer? What species would you pick? Would there be specifications for the selected computer?

Animals, including humans, do not all develop their faculties at the same rate or at the same age. If some arbitrary set of developments were to be chosen, it would need either an enormous amount of testing of the developing faculties, and a comparative valuation of each type of development, or choosing an arbitrary time close to adulthood. Both alternatives would be untenable. But what would be the criteria and how would we make the choice?



So now I have discussed what life is, and how an individual life is more than just being alive. Also, four different biological criteria have been examined to see where the dividing line is between being alive and having an individual life. But none of the criteria produce a definitive or agreed dividing line. It might be argued that the significant criteria are not biological.

Perhaps there are other criteria, and they might not be biological. I leave it to you to make your own decision.

But how you make the decision will depend on why you want to. Perhaps to calm your conscience? Or to blame someone?

I had better not say any more.