“Life Begins at Conception”


I found myself recently in another one of those online religion-vs-atheism arguments, this time following the controversial Twitter remarks of Richard Dawkins on the morality of allowing a Down Syndrome foetus to run to a full pregnancy term, rather than terminating it in favour of a ‘healthy’ pregnancy.  Of course, despite Dawkins’ attempt to explain his position thoroughly and apologetically, the holier-than-thou brigade have continued to demonise him and ignore the logic of his explanation.

However, the core topic of that particular discussion is not what this post is about.  Rather, I want to focus on a related issue that came up in the course of the ‘debate’, which was basically about abortion.  Much of the religious opposition to Dawkins was concerned with the dogma that any deliberate termination of a foetus was immoral because it equated to the taking of another human life.  It is this point that I took exception to, because there is no universally-agreed moment at which a human life begins.


In terms of defining when legal abortions can take place, this varies among western countries.  It is subject to debate, informed by scientific and medical experts primarily on the basis of how mature and responsive the central nervous system is at any given stage. Of course, a particular stage of development of the brain and nervous system does not provide any basis for marking where a human life begins.  Instead, it provides at least a guideline for scientific and medical experts to make a judgement about what kind of pain or suffering could be experienced by a foetus. This in turn allows law-makers, and society-at-large, to draw a (somewhat) arbitrary line at a particular stage of foetal development, up to which they are mostly ‘comfortable’ with elective terminations.

However, defining ‘human-ness’ is even harder than this. 

Prenatal “Human-ness”

Few would likely argue that a healthy newborn isn’t fully human.  It has all the physical features of a human and it is recognised, loved and valued as such by its family. But the newborn is not likely to be self-aware in the same sense that an adult or even an older infant is.  It has no conscious concept of the human society that it has just been born into. It has no ability to formulate or enact decisions and is totally dependent on others for its survival. Despite this, we generally accept that a baby is fully human – a legitimate member of our society.

One could argue that until a baby has been born alive that it is not yet human, because it is not a participant (not even passively) in any human society.  However, most folks would reject this, particularly an expectant mother, who might claim that they have already been bonding with their child while it is still in the womb.  Furthermore, there is not a great deal of physical difference between prenatal baby in the final weeks of pregnancy and postnatal one. Hence an argument that “human-ness begins at birth” is not one that will ever likely find universal agreement.

I argue that ‘human-ness’ isn’t a quality for which we can have any kind of useful scale.  While we can identify stages of prenatal development and reasonably describe various features and functions as being more developed, there is no point in talking about a foetus being ‘more human’ according to this timeline.  The pro-life / anti-abortion movement will probably agree with me on this point.  However, this is likely where our agreement will end if they choose to claim that a human life begins at the moment of conception.


The term ‘conception’ has been used and defined, primarily by Christians and more specifically by Catholics, as the moment when a human life begins in utero.  And this is indeed a convenient and intellectually satisfying label, because it refers specifically to the fertilisation of the mother’s egg by the father’s sperm.  The combining of the separate DNA of two people to create the new and different DNA of a new individual.  It’s not possible to have a more specific start-of-life-defining-moment than this, right?

Furthermore, modern science has even helped us to define this moment – after all, it is only relatively recently in human history that we’ve had the techniques and the understanding to recognise what genetic material is and how it combines during sexual reproduction.  We now know that a zygote is uniquely different to the individual gametes from which it is formed.

But let’s step back from this apparent physical reality for just a moment, and at least recognise that this claim is more a philosophical than it is a practical one. As well as providing us with the knowledge of gametes and zygotes, modern science and medicine also tell us that between one third and one half of all fertilised eggs are lost spontaneously (aborted) early in the first trimester of pregnancy and often before the woman even knows that she is pregnant.  Spontaneously aborted embryos are almost never (as far as I know) mourned as losses, either by the mother or by society at large. These types of losses can be reasonably characterised as ‘biologically natural’ – in fact they are often due to chromosome abnormalities or other biochemical factors that are just not compatible with a healthy pregnancy or offspring.

Lost embryos and zygotes are not considered to be human deaths by most people and by society at large. We do not hold funerals for them, and don’t recognise them as ever truly being human.  Hence the claim that a zygote (the scientific label given to the result of a conception) is a human is at best a philosophical claim only, not one that applies in practice.  Let’s return to this point later.

 The (Abridged) Biochemistry of Conception

If we’re going to rely on the moment of conception as our definition for the start of a given human life, then we should understand this as clearly and as specifically as possible.  As described above, the ‘pro-conceptionists’ will claim that they’ve got this pinned: The combining of the separate DNA of two people to create the new and different DNA of a new individual.

However, this description is not a single event. It is a process – a cascade of numerous, complex events that really have no specific beginning or ending.  When we use a word like conception, we need to understand that this is an artificial label that we apply, with some arbitrariness, to the events that start with approximately the time that a sperm enters an egg, and ends approximately with the formation of a zygote before it divides into the so-called daughter cells of the new embryo.  These events are not exact, unless one can give a very precise – in fact, an infinitesimally precise – definition to the specific biological events involved.

In particular, consider the (approximate) moment when a sperm cell bonds to the cell membrane of the unfertilised egg.  Do we have a new human life at this point? Most will argue no, because the key criterion in defining life from conception was concerned with the combining of the separate haploid chromosomal complement to make the diploid complement of the resulting zygote. Technically, this combination happens as the in-process zygote is preparing biochemically for its first mitotic division.

Despite the animated descriptions in various youtube videos of the fertilisation process (and there are some good ones out there), the combination of the sets of DNA is not a temporal singularity. In other words, it is not an instantaneous event – it takes some time, even though it may be short, for that to occur.

 How Much Genetic Material has to Combine?

If you’re going to insist on calling ‘conception’ the unique new-human-moment, you need to ask yourself if this process were to be halted after, say, 10% of the separate DNA material was combined, would you have lost a life at this point?  Surely it makes no sense to think of this moment as being only 10% of a new human life.

What about if it reaches just over 50%?  Does a half round up to the full?  An undergraduate biologist will be able to tell you that 50% of a chromosomal complement is a long way from compatibility with life, and if this were indeed the biological result, the outcome would be one of those spontaneous embryonic abortions referred to earlier.

Well, what about at 100% combination then?  Again, no, because a diploid complement that was missing a very small proportion number of chromosome pieces here and there – depending on which ones they were, could certainly be compatible with life.  This is not uncommon in fact, because bad genes on one chromosome are frequently compensated for by those on the ‘good’, matching chromosome.

The problem with this proportion-of-DNA-combination approach is that there is no number that can apply in any given case, because it all depends on which pieces of DNA combine successfully. One only has to extend this understanding to recognise that there are no unambiguous biological criteria for defining the instant of when not-a-new-human-life material switches to become definitely-a-new-human-life material.

Therefore, if one persists in saying that conception is the moment, because that’s when maternal and paternal DNA is combined into a new cell, then one is still equivocating on the precise, singular moment of human-ness. The process of conception actually occurs within a smear of time, with no specific beginning and no specific end.

And so we come full circle to Richard Dawkins, who has described other natural processes in similar terms in his 2011 article on The Tyranny of the Discontinuous Mind.

A Philosophical Argument

There are two objections I’ve encountered to this observation. The first is that this argument doesn’t matter, because even at the moment of the sperm meeting the egg, or upon penetrating it, we already have a potential new human anyway.  However, this counter-argument misses the key point that one’s decision of when a potential new human begins is still entirely arbitrary. With this viewpoint, one could say that they were a potential human as soon the gametes within their own parents’ cells were formed, or even trace a pointless regression back through one’s ancestral genetic formations to the very beginning of life on earth.

The second objection I’ve heard is that biochemically dividing up the events at conception like this is ‘splitting hairs’, with a reference to Zeno’s paradox thrown in. (I had never heard of this before, so I had to look it up before I could determine that it was (or rather, they were) irrelevant to the issue).  Superficially, this objection seems to have merit. Because yes – in dissecting the process of human fertilisation down to tiny time slices, in which we could hypothetically observe the progressive appearance of diploid DNA, we’ve gone beyond the practical definition of conception and the practical account of what makes one human.  However, when we’re dealing with biology on the scale of ‘conception’, as discussed above, we’re no longer in the realms of practicality. We’re in the murky, ambiguous, equivocating and unresolved depths of philosophy.

So finally, if you must insist on sticking with the label of ‘conception’ as your definition of the start of human life, you really ought to think it through. Understand that not only does your label have no practical relevance, but it is philosophically flawed as well.