Embryology and the beginning of life

When does life begin?

“No one knows when life begins”

What about foetal development?

When is the first heartbeat?

When does consciousness begin?

When can babies feel pain?

When is viability?

Which terminology is most accurate?

Is the foetus a parasite?

Does twinning suggest life doesn’t begin at fertilisation?

When does life begin?

As explained in ‘Why pro-life?’, this is a scientific question. 81% of laypeople say that biologists are the experts to answer this question, and ‘life’ is clearly a biological concept. But perhaps the reason there is some disagreement in the general public is because the question as phrased is somewhat ambiguous. There is a sense in which ‘life’ is continuous – life has existed ever since the first living creature. When an embryo is created, what existed before it was still ‘alive’ – the egg and the sperm cell, for example. Moreover, all sorts of things are alive but not persons – bacteria, for example. Even some human life is not morally valuable in the same way – an individual skin cell, for example. So we should be clearer about what it means to talk about the ‘beginning of life’.

What we really want to know is: when does ‘one of us’ begin to exist – a human being? Since a human being is an individual member of the species Homo sapiens – an individual organism of that species – what we are really asking is, when does an individual human organism begin to exist?

This makes it clearer still that it is a biological question. You might say: I don’t care when a biological human being begins, I want to know when a person begins – but that is just to deny that all human beings are persons, which is a different objection to the pro-life view (see ‘Why pro-life?’). It should not stop you from recognising the basic biology: that there is an individual human organism – a human being – from fertilisation.

In support of this claim, I repeat from ‘Why pro-life?’:

The claim is that human embryos and foetuses are human beings, that is to say, members of our species, Homo sapiens. They are individual human organisms – dependent, but still individual. They (usually) have their own genetic constitution and their own future. They have all they need to develop into a mature human being, other than nutrition and a normal environment. They need these latter two – but so do infants and toddlers, who will also die without nutrition, oxygen, or the care of others.

Bear in mind that no religious scriptures talk about fertilisation; fertilisation was only discovered in recent centuries. So the idea that a new human organism originates at conception is not grounded in religious tradition. On the contrary, it was a scientific discovery in the late 19th century. It was precisely these scientific developments in the 19th century which led to laws prohibiting abortion during this period – and these laws were promoted first and foremost by the medical profession.

That a human organism is created at fertilisation has remained a scientific fact ever since. It is taken for granted in countless works of embryology. A recent survey of 5 and a half thousand biologists from around the world found that 95% affirmed the view that a human organism is created at fertilisation, with the large majority of explicitly ‘very pro-choice’ biologists affirming this view. When people say that they are not human beings, they are more likely making the claim that they are not persons. That they are human beings is not seriously contested from a biological perspective (and 81% of laypeople surveyed in the same paper said that biologists are the experts on ‘when life begins’, so the biological perspective is clearly what most people have in mind when they talk about the beginning of life. As Ann Furedi, former CEO of the UK’s leading abortion provider, put it:

‘We can accept that the embryo is a living thing in the fact that it has a beating heart, that it has its own genetic system within it. It’s clearly human in the sense that it’s not a gerbil, and we can recognize that it is human life … The point is not when does human life begin, but when does it really begin to matter?’

For a more thorough discussion of these claims, see Condic (or here) or George and Tollefsen.

See also my published paper on this topic, with Alexander Pruss, along with my other academic papers here: https://calumsblog.com/academic-papers/. It comes at the topic from a slightly different angle (responding to a specific objection that there is no change of identity at fertilisation) but may still be helpful.

“No one knows when life begins”

As suggested in the previous answer, this is not true. We do know. The genuine question is whether all human beings are persons – individuals with full moral status.

Hence, the opinion of the US Supreme Court in Roe v Wade (1973) was clearly mistaken insofar as it depended on this claim: ‘We need not resolve the difficult question of when life begins. When those trained in the respective disciplines of medicine, philosophy, and theology are unable to arrive at any consensus, the judiciary, at this point in the development of man’s knowledge, is not in a position to speculate as to the answer.’

These professions are only uncertain because of the ambiguity of ‘the beginning of life’. When the question is actually clarified – the beginning of an individual human being – biologists have had an answer for around two centuries.

Consider another implication of suggesting that we ‘don’t know’ when life begins, and therefore we should let people decide for themselves. Wouldn’t it allow some people to say that life does not begin until a child is rational – several years into their life? Or even that it does not begin until the brain is fully developed, at around age 25? Why should we prevent people from performing infanticide, if they sincerely believe that life has not begun at that point, as many cultures throughout history have done?

Clearly, there is no problem with imposing one view of ‘when life begins’ over another. We already do so in the case of infanticide. That is because we do, in fact, have knowledge about when life begins. We know it begins before the infancy stage of human development. In fact, we know that it begins at fertilisation.

What about foetal development?

For an overview of foetal development, see my book chapter on the topic, which will be continually updated over time.

I also highly recommend https://www.ehd.org/ as a fully referenced summary of foetal development. It also has live videos of embryos inside the womb from around 4-8 weeks (some longer clips available here). In the videos section of my website I have collected together a few relevant videos as well.

NB: there is a difference of 2 weeks between gestational age (since last menstrual period) and embryological age (since fertilisation). Hence, if you see a discrepancy of 2 weeks between a claim of mine and the reference cited, this is the reason.

When is the first heartbeat?

It has recently been suggested that this is a contentious issue, in the light of ‘heartbeat bills’ in the US banning abortion from the time a foetal heartbeat is detectable. This is dishonest, because there is no real controversy within the scientific community. The first heartbeat occurs at around 22 days after fertilisation, and this is standardly recognised without hint of controversy. For example, in 2020, researchers from the University of Oxford’s Division of Cardiovascular Medicine, noted in their basic introduction to cardiovascular embryology that ‘The initiation of the first heart beat via the primitive heart tube begins at gestational day 22, followed by active fetal blood circulation by the end of week 4’.

In fact, the University of Oxford recently announced research suggesting that the first heartbeat was even earlier, perhaps as early as 16 days (original paper). Again, the researchers displayed no hesitation about calling this a ‘heartbeat’. In fact, even Planned Parenthood, at the forefront of heartbeat denial, describe this as a ‘beating heart’ on their website.

It is claimed that this is not really a heart or a heartbeat, but ‘a grouping of cells that are initiating some electrical activity’. But for those who may not have gone to medical school, that is essentially what a heart and a heartbeat are. The heart is composed of cells, which initiates some electrical activity (from the sinoatrial node), which causes the heart to contract, i.e., pump. Presumably the pumping was left out of this account because some people might realise that this sounds a little too much like a heartbeat.

Secular Pro-Life has a helpful collection of articles about this recent instance of science-denial by the more extreme wing of the pro-choice movement, including this article. My favourite example (described in full here) is when a proponent of this pseudoscience backed up her somewhat hubristic article by saying that ‘Any basic embryology textbook’ explains the formation of a zygote at fertilisation, not a foetus. Unfortunately, the ‘basic embryology textbook’ she chose to cite was yet another textbook confirming that ‘The heart begins to pump fluid through blood vessels by day 20’.

In summary, the human heart begins to beat probably between days 16-22 after fertilisation. To say otherwise can only be described as pseudoscience. We should, in fact, be appalled that certain medical authorities are colluding in this deception.

When does consciousness begin?

Obviously, no one really knows when consciousness begins. Even attributing consciousness to other adult humans involves some philosophical assumptions, though most of us are confident in the case of human adults. When it comes to animals, we are far less confident, mainly because we know so little about what, exactly, causes consciousness. This is a philosophical problem as much as anything. Although there is no reasonable doubt that foetuses are conscious by the early third trimester, and there is no longer much reason to doubt that they are conscious in the second trimester, whether they are conscious in the first trimester is extremely difficult – if not impossible – to assess.

The baby’s first non-reflexive movements – indicating substantial neurological development – begin at just 4-5 weeks after fertilisation, reflexive movements beginning shortly after. Brain waves are detectable from 43-45 days at latest (and perhaps earlier). From 12 weeks, babies can make purposeful movements towards their twin, taking special care around their twin’s eyes. Further details of landmarks later in pregnancy are available in my book chapter, but in my view the purposeful movement towards their twin is sufficient evidence for us to be relatively confident that babies 12 weeks after fertilisation (14 weeks’ gestational age) are conscious.

It is sometimes thought that the embryo does not look human in the first trimester. This is not really true, but in any case, one of the main differences between embryos and adults is one of proportion. The embryo’s head is, after a few weeks, enormous compared to the rest of its body. But that is precisely because the brain is so big. By 8 weeks, the brain is 43% of the baby’s bodyweight, and by 11 weeks, the forebrain alone has 3 billion neurons.

The evidence that babies can feel pain as early as 10 weeks from fertilisation is also relevant, since it is only possible to feel pain if one is sentient.

When can babies feel pain?

It is virtually certain that babies feel pain by 23 weeks after fertilisation (21 weeks since fertilisation). See the videos section of this website for videos of babies at 23 weeks, and 28-34 weeks, responding to an anaesthetic injection. In my view, it is not possible for any sane person to doubt that these babies are experiencing pain.

The Royal College of Obstetricians and Gynaecologists claim that it is doubtful whether babies even by this point feel pain, since they would be too heavily sedated by the ‘warm, buoyant and cushioned’ environment, and chemical factors like adenosine. But it is obvious that the babies in these videos are not sufficiently sedated by these factors. I work in surgery. If a supposedly anaesthetised patient made these facial reactions in response to an injection, we would quickly conclude that they were very much awake.

The RCOG also claim that pain is not possible at all before 24 weeks, since connections from the periphery to the cortex are not intact, and the cortex is needed for pain sensation. Of course, this claim is also straightforwardly disproven by the 23 week fetus in the video which clearly has a cortical response to a painful stimulus. But perhaps we can allow a small margin of error.

A more problematic development for the RCOG is that one of the lead authors of the report, Stuart Derbyshire, who is the world’s leading authority on fetal pain, and himself still pro-choice, has since changed his mind and believes that pain may now be possible from 12 weeks’ gestation (10 weeks after fertilisation). He says that despite claims of a consensus, ‘there never was a consensus that fetal pain is not possible before 24 weeks’, noting many papers which have ‘speculated a lower limit for fetal pain under 20 weeks’ gestation… Regardless of whether there ever was a consensus, however, it is now clear that the consensus is no longer tenable.’

Derbyshire and his co-author, John Bockmann, make two primary points: first, there are in fact functional projections from the thalamus to the cortical subplate from 12 weeks, which are equivalent to later thalamocortical projections (previously thought to be necessary for conscious experience of pain). Moreover, however, the authors doubt whether even the cortex is needed for pain sensation, noting a case of preserved pain sensation in a patient in whom the cortical areas normally thought necessary for pain were almost entirely destroyed. In addition, others have noted that many children with anencephaly or hydranencephaly, in whom the cortex is absent or almost absent, are clearly sentient and able to feel pain. Given that the primary objection to fetal pain prior to 24 weeks has been the necessity of thalamocortical projections, it appears there is no longer any good reason to doubt the possibility of pain prior to this point. Hence, fetal pain may well be possible from 12 weeks or earlier.

Other authors have suggested the possibility for pain even earlier.

When is viability?

Viability – the point at which a baby can survive (with medical assistance) outside the womb – obviously differs enormously depending on place and time in history. The graph shown here demonstrates the proportion of babies surviving at <1000g (around 28 weeks, usually) at given times in history. Clearly there was a huge improvement in the second half of the 20th century, which has persisted to this day. Although viability is now often assumed to be 24 weeks, in reality babies have survived much earlier, with the record holder being Curtis Means, born at 21 weeks and 1 day. In fact, survival rates at 22 weeks are not at all bad: a recent systematic review found that survival rates when 22 week babies are actually given treatment is around 43.6%. For this reason, clinical guidelines are gradually moving towards standardly considering resuscitation for babies born at 22 weeks, who would previously have been thought to have no hope and so left to pass away peacefully.

Which terminology is most accurate?

Pro-choicers often criticise pro-lifers for using ‘inaccurate’ or ‘unscientific’ language when they, for example, call the embryo or foetus a ‘child’ or ‘baby’.

This is highly misleading (or false). It is a confusion between inaccurate terms and non-technical terms. Non-technical terms can still be perfectly accurate – ‘axilla’ is the technical term for ‘armpit’, but ‘armpit’ is still perfectly accurate, and doctors use it all the time. Likewise with ‘myocardial infarction’, the technical term for a heart attack.

The reality is that doctors and academics (I am unfortunate enough to be a member of both categories) frequently use the term ‘child’ or ‘baby’ for a human foetus.

Take the term ‘child’, for example. This is, in fact, an accepted term in international law – there is a Convention on the Rights of the Child. And that Convention states clearly in its preamble that children need legal protection ‘before, as well as after, birth’. Hence in international law there is such thing as an ‘unborn child’. This is impossible to dispute. Likewise, in medicine, the foetus is often referred to as a child. The Oxford Handbook of Obstetrics and Gynaecology has no hesitation about referring to the ‘unborn child’ on multiple occasions. For example: ‘it is considered unethical to deny treatment to an HIV +ve mother as this treatment would protect her unborn child and potentially her own health.’ The simple reality is that it has never been unacceptable or inaccurate to refer to the foetus as an ‘unborn child’ within law or medicine.

Likewise with the term ‘baby’, which the same textbook refers to on various occasions, as does the NHS website. If you’re really in doubt, simply search ‘unborn baby’ or ‘unborn child’ on Google Scholar, and see how many results come up. In fact, a recent systematic review in one of the leading Midwifery journals concluded that “Midwifery scholarship, global midwifery professional bodies position statements and practice codes mostly employ the word ‘baby’ instead of ‘fetus’.”

The idea that ‘unborn child’ or ‘baby’ are ‘unscientific’ terms is, frankly, absurd. These terms are used constantly in clinical practice, and often in academic and medical textbooks as well. The attempt to remove them from terminology looks more like politically motivated euphemism than serious science or linguistics.

Is the foetus a parasite?

No, this claim is absurd and dehumanising. The use of ‘parasite’ language to describe undesirable human beings has an unpleasant history (to put it mildly) and we should be very careful before wielding it to speak about any humans ever again.

In fact, however, research suggests that, in general, pregnant women have a significantly lower risk of death than non-pregnant women (see ‘Abortion is 14 times safer than childbirth’), and the unborn child shows substantial symbiosis with the mother: for example, sending its stem cells around the mother to repair tissue and act as surveillance cells against various cancers.

No biologist refers to pregnancy in general as parasitism. But if an unwanted pregnancy is parasitism, it is hard to see how all pregnancies shouldn’t be: all pregnancies in all species involve certain risks to the mother and help to nurture the child, regardless of whether the child is wanted or not. There is just no scientific sense in which this could reasonably be called parasitism. This is a meaningless slur.

Does twinning suggest life doesn’t begin at fertilisation?

This is occasionally raised as an objection to the view that life begins at fertilisation. But the argument is rarely actually explained, and it is difficult to identify what the argument actually is.

Here is one version of the argument:

  1. If X can split into two organisms, Y and Z, then X is not an individual organism.
  2. Until a certain point after fertilisation, the blastocyst/embryo can split into two organisms.
  3. Therefore, the blastocyst/embryo is not an individual organism.

The problem with this argument is that there is just no reason to believe that premise 1 is true. In fact, there is decisive reason to think it is false. There is a fairly obvious counter-example: pregnancy itself. In pregnancy, a woman ‘splits’ into two new organisms: the mother and child. But clearly this doesn’t mean that there was no individual organism before, and nor does it mean that the original organism disappears.

Another way of making this objection is to say that if the splitting of the original organism is relatively symmetrical, then the original organism disappears and two new organisms begin. This might be thought to be morally strange: it suggests that we have a moral reason to avoid twinning.

In response, first, there is some evidence that even at the two-cell stage, the organism is not symmetrical, and hence there is no clear reason to think that the original organism is destroyed. But suppose the original organism is destroyed: is this as morally counter-intuitive as we might think? As I explained under ‘How can killing an early embryo be seriously wrong?’, our moral intuitions on early embryology are likely highly unreliable, and given that twinning (and especially higher multiples) are significantly more dangerous for mothers, it does not seem counter-intuitive to say we should avoid twinning if possible – that it might be a pathological process (that happens to usually have perfectly happy results).

Perhaps there is a more robust argument from twinning, but I haven’t seen one: clearly an individual human organism can exist even if it then splits into two. So this does not impede the claim that an individual human organism is created at fertilisation.


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