The moment a baby’s brain starts to function, and other scientific answers on abortion

Nobody can say when an individual life begins, but the facts can help show when a life does not begin

There are not two views on abortion in Ireland. There are 4,803,748 different perspectives. In the weeks leading up to polling day, the Irish people have started from the ground up and the debate is now firmly in the parameters of “under what circumstances should abortion be available?”

Scientists are generally a stroppy sort of people. We are trained to question absolutely everything, and we have a deep scepticism of authority or unjustified assertion. We make individual conclusions based on an objective assessment of the evidence and – beyond the core accepted scientific facts – we disagree with each other constantly.

Since last week, 1,500 Irish scientists – ranging from PhD students to Ireland’s only Nobel Laureate for the sciences – have signed a letter written by Scientists for Yes, summarising our views on abortion.

Each one of those 1,500 individual scientists has their own distinct moral values, whether religious or secular. Each of us assessed the social and scientific evidence surrounding the issue of abortion in society and each arrived at her or his own unique, personal stance, and how best to manage abortion in Ireland.


All 1,500 disparate views have one thing in common; that Ireland must repeal the Eighth Amendment to the Constitution. This accord of diverse opinion was also captured in the general population in 2017; through a poll commissioned by Amnesty International, through the Citizens’ Assembly and also by the vast majority of members of the joint Oireachtas committee.

Polarised referendum campaigns can stop people from listening and looking at the evidence. As we approach polling day, there are a number of pieces of evidence – social and scientific – that Scientists for Yes believe may be valuable, as the public come to their own conclusions:

1. Brain development

When does consciousness begin? For most people it is a functioning brain that defines a human being, as this is where our thoughts, feelings, and conscious minds come from. Some people are concerned with abortions after six weeks of pregnancy because that is when a basic spinal cord and nervous system first develop, but it is not until week eight (six weeks post-fertilisation) that the first rudimentary brain activity – the kind that is observed in organisms as simple as insects – can be observed. The very beginnings of our higher brain structures only start to appear between weeks 12 and 16. Crucially, the co-ordinated brain activity required for consciousness does not occur until 24-25 weeks of pregnancy. We cannot say when consciousness first emerges, but it cannot rationally be called before the end of the second trimester at 24 weeks of pregnancy.

2. Evolution and human uniqueness

The issue of humanity or humanness permeates all discussion and thought about foetal development. A useful perspective in thinking about this topic comes from evolutionary biology.

As humans we share common ancestry with all life on Earth, and this is reflected in our development. In the first few weeks of development human embryos are indistinguishable from fish or bird embryos. For many weeks after that we are recognisable as mammalian embryos, with a heart and a basic brain, but are anatomically no different from mouse or pig embryos at similar gestational stages. Eventually at week 10 (8 weeks post-fertilisation) the embryo begins to develop into a visually recognisable human embryo due to early face development.

3. Mental health

Some ‘No’ campaigners argued that mental health should not ever be grounds for an abortion even under current law. But all mental health disorders, without exception, are brain disorders. Sometimes they are caused by an internal chemical problem in the brain, in the way that a cancer can be caused by cellular problems in an organ. Sometimes they are caused by the organ’s response to the environment, in the same way that stress causes heart attacks or smoking causes lung cancer. But in all cases, mental disorders are due to effects on the brain itself and must be treated and managed according to the same framework as any medical disorder.

4. Disabilities

There has been genuine concern across the board of genetic abnormalities and disabilities being targeted for abortion. Let us be clear that the Government’s proposal rules out viable disability as justification for an abortion. Regardless of abortion, existing genetic screening methods at pre-implantation stages can reduce the proportion of genetic abnormalities, though Ireland is highly conservative in permitting this.

5. Conception

Many believe that a human being is defined by a unique human genome, and a new life begins at conception. Nobody can really tell you when an individual life begins, however depending on your values, the facts can help show when a life does not begin.

A genetically unique cell called a zygote is formed at fertilisation (normally two weeks into the gestational period). This divides into a “blastocyst” over the following seven to 10 days, until implantation in the womb at three weeks. The implanted blastocyst becomes an embryo at eight weeks, and can only begin to be considered an immature foetus by 11-12 weeks.

If life begins at fertilisation, then the morning-after pill, which is legal and accepted in Ireland, is a form of termination that would be morally indistinguishable from a late-term abortion.

6. Organ development

Some campaigners have incorrectly stated that the formation of organs in the first trimester means that a baby is fully formed by week 12. While most organs are indeed present as very basic structures by week 12 of pregnancy, they are in fact missing many crucial components and some, such as the eyes, liver and pancreas are only beginning to develop. Importantly, the thalamus (necessary for pain and conscious perception) does not appear until the end of the second trimester, and the folding of the cortex does not develop until the third trimester.

7. Prevalence

Many voters are concerned about the prevalence of abortion, and that legalising it may “open the floodgates”. We just need to look at many countries, such as Switzerland – a country that introduced abortion by popular vote – who have managed to maintain a relatively low abortion rate due to efforts in sex education, contraceptive availability, and social safety nets.

The total legal abortion rate in Switzerland is only 6.8 per 1,000 women aged 15-44. The Iona Institute estimates that the illegal abortion rate in Ireland, due to abortifacient pills alone and excluding procedures carried out abroad, is 5.7 abortions per 1,000 women in Ireland and others estimate that rate to be as high a 7.7. The evidence clearly suggests that the legalisation of abortion can be a tool to reduce it.

8. Survival:

Much of the discussion in this debate, on both sides, surrounds the question of how best to protect the embryo or foetus. Biology can give us a crucial insight here. It’s not the judicial system, or the healthcare system, or even the education system. It’s not the State, or a population of uncertain voters. It’s the individual woman who, like any mammal trained by 400 million years of evolution, will sacrifice herself to ensure her children’s survival and wellbeing. It is not possible for there to be a more dedicated guarantor of a foetus than the woman carrying it.

Dr Tomás Ryan is assistant professor of neuroscience at Trinity College Dublin and spokesman @ScienceForYes