When does human life begin?

September 12th, 2015 in Life. Tags: , , , ,

Difficult issues series


We have seen (Who were the first human beings?) that it is difficult, perhaps impossible, to say when in natural history the first human beings existed. Quite possibly it was a gradual process over thousands of years.

This leads on to a related question: when in the process of sexual reproduction does human life begin?

Different approaches

There is little consensus on the answer to this question – people take many different approaches:

Common sense?

For many, this is a simple matter of common sense. But unfortunately they don’t always agree on the answer. Is it conception, or when there is a heart beat or movement, or when the baby can survive outside the womb?

We will look further at these possibilities, but it seems we need something more objective than common sense to arrive at a convincing answer.


A fetus is a member of the species homo sapiens, and soon after birth it has human DNA which determines human growth and characteristics. However, while DNA defines us as a human being, it doesn’t define life – dead people still have DNA.

Comparisons between birth and death

One reasonable argument is to base our view on what doctors and law courts consider are vital signs whose absence indicates death. There is still some controversy even about this, but there seem to be four main views about the definition of death (with some matters in common):

  1. US law says “An individual who has sustained either (1) irreversible cessation of circulatory and respiratory functions, or (2) irreversible cessation of all functions of the entire brain, including the brain stem, is dead.”
  2. Death is “the irreversible loss of the capacity for consciousness, combined with the irreversible loss of the capacity to breathe”, or
  3. death occurs when “the brain can no longer function”, or
  4. human beings die when they no longer function biologically as organisms”.

It seems reasonable then to use one or several of these as criteria for the commencement of life.

However these result in very different determinations of the beginning of life. The fetus begins to function as an organism shortly after conception, the heart begins to beat after 2-3 weeks, the brain forms gradually, but can be considered to be working after about 8 weeks, but breathing doesn’t begin until birth.

Cells vs organism

The Westchester Institute for Ethics and the Human Person considers the early moments of conception, and the difference between a human cell and a human organism. It argues that there is a clear scientific approach to distinguishing different types of cells, based on “differences in either composition or behavior”, and that an organism is “(1) a complex structure of interdependent and subordinate elements whose relations and properties are largely determined by their function in the whole and (2) an individual constituted to carry on the activities of life by means of organs separate in function but mutually dependent: a living being.”.

On this basis, it is said that a moment very early on in conception, when a zygote is formed, satisfies these requirements, therefore a zygote is an organism, and this is when human life begins.

Other scientific approaches

RationalWiki lists five scientific approaches to determining when life begins (some of which we have covered already):

  • Metabolism (i.e. cellular activity). But this exists in sperm and egg cells, and can continue after death, so it probably isn’t a reliable indicator.
  • Genetics: “a genetically unique person begins at conception”.
  • Embryology: about 2 weeks after fertilisation, “a simple ball of cells begins to grow into a fully functioning being!”, a process known as “gastrulation“.
  • Neurology: the brain begins to function at about 8 weeks, but the full pattern of brain function as measured by EEG occurs only at about 24-26 weeks.
  • Ecology/technology: it is also around 22-26 weeks that the baby can survive outside the womb.

RationalWiki concludes that this isn’t a question that can be resolved by science, and notes: “the potential for human life can begin very early, but it is personhood that is the sticking point”.


Geneticist and author Ricki Lewis identifies 17 possible points in the process of conception and birth that could be considered as the beginning of life. She opts for the time (about 22 weeks, she says) where a “fetus has a chance of becoming a premature baby if delivered”.

Lewis goes on to agree that this makes this choice technology dependent: “Until an artificial uterus becomes a reality, technology defines, for me, when a human life begins, rather than biology.”

Spirit or soul

People who believe that human beings are more than merely physical, especially religious people who believe we have a “soul”, will naturally consider the point at which a human develops or is joined with a soul to be the point where human life begins. But this doesn’t help as much as you might think, because people think this event occurs at different points.

  • the common christian view is that it occurs at conception;
  • some say it is at “quickening”, when the baby first moves (generally about 3-4 months);
  • Jewish and some other traditions say the soul enters the body at the first breath;
  • if we follow the logic of the gradual growth overtime of pre-human species into human species (see Who were the first human beings?), then there is no single point in time, but a gradual process of becoming a human being.


Many suggest that we should be asking when the fetus becomes a person, not just a living organism. This may seem like the same question, but may point to the development of consciousness, which probably occurs sometime after 22 weeks.

Wrong question

There are those who say this is the wrong question. We cannot define life or when it begins, we should simply make choices affecting the fetus or baby based on what will causes least pain and not take away anything that will be felt as loss. This emphasises practical humanity, but could result in post-birth babies being treated in ways most people would regard as unethical.

Assessing the views

There isn’t a clear objective answer

All these criteria make it impossible to say with certainty when human life begins, unless we hold to a dogmatic position based on a particular worldview. Our opinion on abortion (which I’ll examine in an upcoming post) will likely determine our view on when life begins, rather than the other way around.

Some views are weaker than others

Among the many views on when human life begins, some seem to have little basis in any objective criteria, for example:

  • The formation of unique human DNA seems to me to be a basis for humanity, but not of life.
  • The viability of the baby outside the womb depends on the technology available, which is based on location and time in history, and is changing all the time. It doesn’t seem that the beginning of human life can be so variable. This criterion may be useful for some questions, but I don’t believe this is one.
  • I can’t help felling that personhood (i.e. consciousness and character) is not the same as human life – an unconscious person on life support is still apparently human.

The strongest arguments?

It seems to me that the two points with the strongest arguments in support are conception (when a human organism with full DNA and potential is formed) and about 10 weeks (when brain and heart are functioning, thus paralleling the criteria for identifying when life ends).

A range of gradual growth?

I wouldn’t claim to have a clear answer, but I lean towards thinking that human life appears gradually – in which case a range may be a better way to define the emergence of human life. This range should surely begin at conception, and probably end at about 10 weeks when both heartbeat and brain function are present.


I think we should avoid being dogmatic, but I conclude that human life begins either at conception, or gradually in the first 10 weeks of pregnancy.

I don’t want anyone to think that this necessarily determines my view of the ethics of abortion (a topic I’ll address soon), but I do think it is relevant to the question.

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Photo Credit: Jason Lander via Compfight cc.

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  1. I would suggest that human life begins at that point when natural processes have begun that, barring unforeseen circumstances, will predictably result in a human baby. Human development and change is constant and continuous from conception until death (and perhaps even after death). Our physical form and mental capabilities are conditions of our state, not our humanity.

  2. You have certainly compiled an enormous number of legitimate factors to consider in this important question, and I think it is apparent that not all people who think diligently about this will arrive at the same conclusions.
    But I think you hit upon perhaps the most inadequate foundation for a conclusion to this question: “hold[ing] to a dogmatic position based on a particular worldview.”
    Thank you for the comprehensiveness of this survey, and I look forward to your post on abortion.

  3. Thanks JWB. It is certainly a case of learning as I go. I wasn’t sure where I would end up on this one, not am I sure how the next post will go.

  4. Hi MATrimble, I can see the logic of what you say, but I think your criterion would result in an egg and a sperm being classed as human life shortly before they meet (“natural processes have begun that, barring unforeseen circumstances, will predictably result in a human baby”), which I don’t think I would agree with. But I understand what you are getting at, and I certainly think conception is the most obvious choice for the start of life, even if I am not sure it is the correct choice. Thanks.

  5. Unklee, it is just I don’t see any other way to make the determination without drawing some arbitrary line that leaves us with humans on one side and some class of sub-human on the other. It is what it is, from that point when we begin developing, we are.

  6. I’m also somewhat confused with the suggestion that a discussion of abortion is to follow. The question of when human life begins defines the whole issue of abortion. Were it not for the fact that a human being is killed in abortion, there would be no more controversy on this procedure than with the removal of a tumor. Presumably everyone agrees that killing innocent human beings is wrong, so the only real question with abortion is when human life begins.

  7. Yes, I agree that it is difficult to draw any other line, but the parallel with when we die is worth considering I think. Re abortion, let us wait and see.

  8. Hi Heather, welcome to my blog, and thanks for the compliment. I found your blog interesting too.
    Hi James, thank you too for the implied compliment.
    I hope you both stick around for the next post where I try to draw the last few posts together. (When I tackle the subject of abortion, I’ll probably need a few friends! 🙂 )

  9. Hi,
    I understand the point of Eric stating that “Our opinion on abortion (which I’ll examine in an upcoming post) will likely determine our view on when life begins, rather than the other way around.”
    In his “Great Divide” book, William Gairdner ( http://www.williamgairdner.com/ ) defends that the those who are pro-abortion (pro-choice is merely an euphemism) use the same tactics that used to be employed in order to defense slavery across the ages: consider a class of human beings as non-human beings, beings of second class, things, etc. Otherwise it is going to be clearly immoral and unacceptable to harm or kill another person.
    But let us expect for your next post =)

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