Talk given to the Atheist Society Melbourne - 8 June 2010
by Graeme Lindenmayer


Does a life start at conception, birth, some time in between, or at a different time altogether? Does this also apply to non-human lives? Heated ethical arguments about such issues can arise when some kinds of research or practices or legislation are contemplated. In this discussion I will attempt to unravel the matter by looking at some aspects of the concept of life, the history of life on Earth, and some characteristics of organisms from the very simple to the very complex.

What is Life?

Life is the property or quality that distinguishes living organisms from dead organisms and 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 living organisms possess four properties:

  1. metabolism – using material and energy from the environment to support continued functioning;
  2. growth – increasing in size from infant to adult;
  3. reproduction – producing new separate organisms, that become similar to their parents, from within the bodies of living parents;
  4. response or adaptation to the environment – taking action needed for metabolism, growth, safety and reproduction.
Other definitions specifically require also that living beings move, communicate, evolve, keep their internal environment stable, have feelings, are intelligent, are conscious or function using chemical reactions (as distinct from electronics). A definition couched in the language of the science of thermodynamics and favoured by Erwin Schrödinger and other quantum pioneers is that living beings are "the class of phenomena which 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." Not only is this very mechanistic, but it doesn’t seem to address growth or reproduction.

Different definitions reflect different views about what life is. 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 if their DNA or RNA gets into cells of living organisms. However, they are given identification by the use of biological names and can be mutated and evolved into new strains, and hence they appear to act as if they are alive. Because of these characteristics, in the practice of medicine viruses are treated in the same way living organisms.

Whatever the precise details of the definition may be, if life is to perform at least some of the four basic functions, then it must depend on a functioning system, that is, a sustainable arrangement of interworking parts. This means that, for a typical specimen of a form of life, its parts, and their interaction must be able to sustain the temperatures and other conditions that act on it in its usual environment.

Origins Of Life on Earth

How did life originate on Earth? Three suggested processes are evolution, intentional creation and reincarnation. (I use the term intentional creation rather than intelligent design for two reasons. A design is not a production process nor the thing designed but only a plan. And also, I want to emphasise the contrast between a deliberate act of intention and the processes of nature where every outcome is just the necessary result of the available materials and conditions of the particular environment they happen to be in.)

From a different perspective, these three suggested processes could be expressed as:

  1. life is an emergent property of matter – which is another way of saying it arose through an evolutionary process;
  2. all matter including fundamental particles is intrinsically alive – which is compatible with the emergent material process, but it implies that life is not a consequence of the way matter is arranged as an organism but is potentially there in all matter;
  3. a supernatural element is necessary to impart the four biological properties to a properly structured piece of inanimate matter to give it life, and, in some versions, to give shape and function to the various kinds of organism – which is compatible with both intentional creation and reincarnation but does not address how the complex bodies of organisms came into being.
Most biologists assume that life developed from inanimate matter through a natural process of evolutionary steps. Increasingly complex chemicals developed in each step. These included types of chemicals that can cause the assembly of copies of themselves when they are mixed with the right ingredients. (Some scientists, notably Chandra Wickramasinghe and Fred Hoyle, have proposed that life on Earth began from life forms or pre-life forms that arrived from outer space. But this does not answer the basic question.) In this concept, the origin of life was not a single event of "switching on": it emerged as a gradual increasingly complex material process.

Some types of self-replicating chemicals occur in nature and others have been manufactured. Scientists have been using them 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 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, and lead to further research into how life could have evolved through natural processes. There is no accepted scientific theory of how living organisms came to exist: Darwin’s theory of evolution addresses only how there came to be different life forms.

It has been speculated that viruses, which display some life-like characteristics, might be an intermediate stage in the emergence of life from inanimate matter. It has also been speculated that viruses began as live cells that mutated. Both of these suggestions seem improbable: all viruses are synthesised inside the cells of living organisms, and all viruses are coated with a very different kind of material from the membranes that cover living cells.

It is often assumed that any extraterrestrial life, such as life on other planets, would have similar origins to life on Earth. Organisms developing in very different environments might need to be structured around different chemicals, such as ammonia instead of water or silicon instead of carbon, or using structures different from DNA. This would make them different from "life as we know it", but, to be life, they would just need to be compatible with the biological (and the thermodynamic) definition.

Some people claim that a life force, is a necessary part of all organisms, so that while natural processes can produce the body, something else is needed to "switch it on", ie., to give it life. The late Australian biologist Charles Birch, suggested that this force is an aspect of the material world. Others say it is supernatural.

Proponents of intentional creation assume a transcendent creator for all life on Earth, and attribute some supernatural (spiritual) aspect to all or some living organisms. This may mean that the creator produced only the very first organism, or the first of each of the different forms which then reproduced naturally, or that each new individual is separately created. There is often the implication that what is alive in each particular organism is the supernatural spirit not the material body, with the spirit usually continuing after the death of the biological body.

Reincarnation means that every life is a spiritual entity that inhabits a succession of material bodies (not necessarily all human) each of which is born (or comes alive) and dies. The beginning of the biological body is of no great concern. The spiritual entity may exist in waiting between the death of one host and the birth of the next. In this concept it is the spirit that gives life to the body. The spirit does not meet the biological criteria of growing, reproducing and having a metabolism. It is thought of as the intelligence and conscious driving force of each body, sometimes with claimed memory of previous incarnations.

In some traditions, reincarnation implies that each serial life remains as a separate entity until such time as it reaches a condition of perfection when it can merge into some universal spirit. There is no explanation of how new sequences of reincarnation come into being as the number of living bodies on Earth increases, nor, if population decreases, whether a sequence can cease without achieving perfection.

Development of Life on Earth

Views about how life originated on Earth have their counterparts in the various views about how it subsequently developed. The evolutionary view, that natural processes produced the diversification and development of life on Earth, is derived from the findings of biological and geological science. The other views either accept some role for natural evolution, including evolution being occasionally nudged onto a new path by the supernatural, or claim that, while variation occurs within species, all species are the consequence of specific creation.

Geological evidence points to bacteria and other forms of life existing at least 2.7 billion and possibly 3.5 billion years ago, but these are thought to be by no means the earliest. Very early living entities would probably have been something like individual microscopic films enclosing RNA or DNA which controlled the organisms’ functioning and reproduction. They diversified into multitudinous forms of bacteria that proliferated and occupied many parts of the earth’s surface. Evidence also points to the appearance, perhaps about two billion years ago, of eukaryotes, ie., 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 protozoans.

In simpler types of single-cell organisms, reproduction consists in the cell growing and then splitting into two cells that are like smaller versions of the original cell. This is referred to as cell division. Cells resulting from the division are occasionally slightly different from the parent cell, 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.

Parts taken from the bodies of some plants and animals can be grown to become mature organisms or body parts. Small parts from some animals, for example planarium worms and some jellyfish, can regenerate into complete organisms provided that they contain some of each type of the animal’s tissue. New plants grow from cuttings or from the culture of individual cells. Organs can be transplanted between compatible animals of the same species. This suggests that the individual cells of multicellular species are separately alive.

In reproduction by division, each "daughter" cell is a half of the parent. Each succeeding generation is, in a sense, just a continuation of its predecessor. All individual organisms have arisen from being parts of previously existing organisms.

Unity of Life

The processes of reproduction, mutation, separation and combination of all life forms on Earth are controlled by DNA and/or RNA. Many types of micro-organism readily exchange segments of their DNA, sometimes incidentally giving recipients new abilities or features. 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 characteristic. There is evidence that exchange of DNA continually occurs between eukaryotes (including us) and bacteria and viruses, with the progeny acquiring, and passing on to further generations, characteristics of both "parent" species. Most eukaryotes have other types of organisms living within their bodies, some providing essential processes for the hosts, and some parasitic. There are very many more "non-human" organisms in a human body than cells of the body itself. It appears that eukaryotes arose as a result of single-cell organisms becoming functionally incorporated into the bodies of other single-cell organisms.

Sexual reproduction employs the fusing of very different types of parts of two biologically compatible but distinguishable organisms, usually of the same species. However, the concept of species, in fact the whole concept of classifying life into domains, kingdoms and so on down to families, genera and species, while very useful, does not mean that life is actually divided into these categories. There are many cases where the distinction between species and between other classifications is not clearly definable.

Most biologists think that all life on Earth is probably descended from the same ancestor, and it seems that all life on Earth has been one biological unity since then. From this point of view there are new arrangements of living matter, but no new beginnings of life.

Individual Identity

Notwithstanding 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 fully grown cell the same entity that it was before it 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. But what about multicellular organisms, which usually do not reproduce by splitting into parts that are each similar to the parent?

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 associations. 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. Then some individual members may become spores, that awaken and produce new colonies when conditions improve, while many of the other members die. These and other types of associations – such as corals, for example, which are polyps 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 when favourable conditions return. In more complex associations, the members form differentiated groups (ie., organs) that depend on each other for survival Failure of an organ such as the heart or kidneys can cause the whole association, ie., the body, to die. The more strongly members depend on each other, the greater the likelihood that all 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 parts to be artificially kept alive, to divide and to 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

Most complex multicellular organisms reproduce through the sexual process – the uniting of two dissimilar cells, such as 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. Sperm cells do not have the functionality that allows them to exist as organisms. Fertile egg cells and seeds and spores initially lack these functions, but they may have the constituents of workable systems that could by "switched on" by some environmental condition.

New multicellular bodies develop from single fertile cell eggs that continually divide into more and more cells which remain coherently associated. And the cells become differentiated into specialised organs. The functioning of all these cells into an organised unit develops bit by bit. By being closely interdependent, the cells in complex multicellular organisms have lost their ability to exist separately. They are alive but are not organisms. So the life of the multicellular organism is the life of the association not of its members.

The process by which eukaryotes reproduce from fertilised female cells differs across the range of species. Plants form from seeds that have to depend on being in a suitable location and supplied with water. Many species, such as some fish, produce sperm and eggs that are fertilised when external agents bring them together outside the bodies of the parents. Many more species produce eggs that develop 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 the start to emerge from their birth shell. The remaining discussion will consider the beginning of the lives of only those species that develop to birth within the body of the mother, with emphasis on mammals.

A newly fertilised mammalian egg may be an association of members, but it is unable to survive independently as an organism. It depends on the active intervention of its environment. If properly protected and nurtured it can continually divide, until at some stage of division and differentiation it becomes a separate functioning adult.

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.

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 mammalian life are:

  1. separation;
  2. independence;
  3. activity;
  4. stage of development ;
  5. degree of being alive

Separation means that the new life is physically separated from or not a part of any other organism. The obvious example is a baby at or soon after birth. But being separate does not necessarily mean that something is, or is yet, a new life. A kidney removed for transplant is not a life, even though it is living. Conjoint twins are not separate but are separately alive and have individual lives.


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 where all the action to sustain life is taken by the environment, as with a new foetus which is completely supported by its mother, and "active dependence" where the organism takes action to secure from its environment its own food and safety. We usually regard such active dependence as independence. But there are different stages of how much a developing body actively 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 attained must be arbitrary. It might, for example, be claimed that the beginning is the time of achieving capability to independently develop the four biological functions. This could be some time after birth.


Activity comprises self-generated motion of all or part of the organism or its interior processing. Seeds and spores are quite inactive and have not yet begun their lives before they begin to germinate. But apparent inactivity does not necessarily mean absence of life. A bacterium that had been locked beneath a Greenland ice sheet for more than 120,000 years was recently revived by scientists at Pennsylvania State University by slowly warming it in an incubator over a period of 11 months. After being placed in a nutritious environment it began producing fresh colonies. When discovered it had been under three kilometres of ice.

Stage of development

Stage of development refers to the progressive acquisition of new faculties and capabilities such as mobility, intelligence, consciousness and self-awareness.

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 responding appropriately in each event. Organisms we would regard as extremely simple or primitive have a range of faculties in a form sufficient for their needs. Having such faculties, at any degree of complexity or sophistication, amounts to intelligence. The gut bacterium Escherichia coli (which we all have living inside us) has at least 30 different sensory systems, for food sources, oxygen, light, pressure and the presence or absence of other E. coli. And it has short-term and long-term memories. We see a gradient in intelligence among life forms (immodestly putting humanity at the top).

Intelligence can be distinguished from consciousness, with things like computers being in some way intelligent but not conscious. Consciousness often but not necessarily includes the ability to feel pain and emotions. And, just as there can be grades of intelligence, there seem to be grades and types of consciousness.

The stage of development that requires consideration from the point of view of morality may not be the beginning of a new life but the beginning of being aware and able to feel pain. This would make virtually all of the species of animal that we eat more worthy of moral consideration than a human embryo or an early foetus.

If stage of development is to be a criterion for deciding when a life begins, it implies a gradation between being alive and having a life – that a particular, arbitrary, degree of being alive is necessary before a new life begins.

Degree of being alive

We usually think of bacteria as being very much less alive than most animals. Individual cells of multicellular organisms must be even less alive than bacteria, even though they grow, divide, self-destruct and also perform the specific functions of the organ they are part of. But they have lost some of the functions that single cell organisms need to survive independently.

When someone dies, although the complex organic whole is dead, many of the organs, limbs and cells are still alive, and can be kept alive for some little time. These body parts would be considered to have a lower degree of life than say a bacterium. A newly fertilized egg (or a virgin egg for species where fertilisation is not always necessary) is no more an individual life than a freshly amputated organ or limb. It is entirely dependent on the actions of a nurturing environment to begin its process of dividing and growing. It may be argued that while an egg may have a lower degree of life than an organ ready for transplant, it has more potential. But as genetic technology advances, any living cell might be potentially developed into a living organism. Cloning is an example. But there is a significant difference between being a life and having the potential to be one.

The crucial question is assessing the degree of life as it increases during the process from fertilised egg to adult, and making a choice from that assessment. I don’t know of any objective way of measuring a degree of being alive, but. intelligence and consciousness may be indicators of it. I don’t know of any objective way of measuring a degree of being alive other than the criteria already discussed. If there is a life force that pervades all things, then a measure of the complexity of an organism might be also a measure of this force, and a proxy measure of the organism’s degree of being alive. But this criterion, like the others, does not give a clear answer.

So none of the proposed biological criteria seem to give a clear-cut answer.

If the reason for making a choice is to enable a decision about issues of morality, the choice is likely to be influenced by pre-existing beliefs. I would suggest that any biological criterion for choosing a time of beginning of a life must be arbitrary but it must be at some time after conception. Also, some of these criteria would put the beginning at a time after a developing organism had acquired the ability to feel pain, and feeling pain might be the more significant moral issue.

This may seem unsatisfactory as an answer: it just shifts the question. But I think the foregoing arguments have shown that the concept of a life is unable to be sharply defined. So the idea of a precise moment of a biological beginning is meaningless.

Supernatural Criteria

The biological views of life are based on observation of the world around us. They accept the rigour of scientific method. But science has nothing to say about spirit. Spirit, for those who believe in it, it is accessible only subjectively – through intuition, or specific exercises of the mind such as meditation, or unsolicited revelation. This does not in itself discredit belief in the existence of spirit nor its significance for life – scientific observation and explanation must also contain a degree of subjectivity. But there is no apparent way of resolving differences of opinion on issues relating to spirit. And these are many.

Two issues may be relevant to the role of spirit in deciding when a life begins.

There appears to be no reference in the foundation texts of the major religions concerning the stage of the development of the body at which this happens. However, over time traditions have built up that it is at conception, or on implantation of the embryo into the womb, or at some other time between conception and birth. These occasions are envisaged for humans only, but could be relevant to all placental mammals. If conception is the answer, then the technique of cloning, which involves the insertion of the nucleus of an unfertilised egg into a body cell that has had its nucleus removed, may present a problem.

The case of non-human species is probably more of an issue for reincarnation where the spirit might inhabit other animals. But some people who do not believe in reincarnation think (some) animals, particularly their pets, have souls. But if the previous incarnations or the pets were, for example, insects or fish, different criteria would have to apply.

Different traditions of belief give different answers to all issues pertaining to spirit, answers that are justified on the grounds of experience and/or faith.


There is no unambiguous way of deciding what life is. Life occurs in many forms, and changes continuously at all its levels of complexity. There is a difference between life as the particular condition of a piece of living material, and a life as a coherent individual living entity. But where is the dividing line between the two, and when does an individual life begin? This discussion has suggested some possible answers:

  1. All life on Earth is one biological entity that began billions of years ago. Parts of it are continually dividing, associating and dying. New organisms are not new lives but new conditions of living material.
  2. All life consists of living cells, which may exist either separately or in a range of associations with other cells. The life of a single cell prokaryote organism begins at the completion of division of its parent organism. The beginning of the life of a complex organism, including a human being, depends on either how many cells you think are necessary (in the case of embryos), or what degree of coherence or complexity or size you think is necessary for the association itself to operate as a coherent entity.
  3. As a multicellular organism develops it acquires degrees of mobility, intelligence, consciousness and independence. Its life may be thought to begin at some arbitrary stage of development of some or all of these faculties.

  4. Biological considerations suggest that the beginning is some time after conception.

  5. The concept of a biological beginning point of a life is meaningless, because of the very complex and fluid nature of life itself. The concept may, however, be useful or even necessary for some purposes of human society.
  6. Each life begins when the development of an organism is sufficient for spirit to enter it, whenever that may happen to be.
  7. Life is essentially spiritual not biological. Spirit determines when a life begins. We may have only subjective ways of knowing when this occurs.
  8. All purported lives are just parts of a single all-encompassing spirit.
Any of these might be relevant to issues such as methods of contraception, abortion, choice between saving an unborn baby or its mother, some aspects of biological research or drowning new-born kittens. (Other considerations may also apply to such issues.)

I know of no way of demonstrating that any answer is valid or invalid. The one you pick will depend on your religious and other beliefs, and on why you want a decision.