“Life begins at conception” is a biological impossibility

Photo by Amir-abbas Abdolali on Unsplash

The idea that a fertilised and implanted embryo is imbued with whatever makes us human at the point of conception is an idea which carries a lot of weight in anti-abortion circles. For a long time, it’s been treated as the starting point from which anti-abortion policies develop. It’s also been treated in most circles as a unprovable argument, something that properly belongs outside the realm of science.

However, it’s not outside the realm of science. “Is a one-minute-old embryo an individual human life?” is a question that can be answered clearly and decisively with the word NO. It’s formally impossible, without resorting to appeals to the supernatural, to argue that a human life is present in that embryo.

Identical twins

The proof that a human life does not begin at conception is not a difficult or technical one to understand, either. It can be understood by anyone who can understand the basic biology of how identical twins come to be.

Briefly, identical twins are born from a single fertilised egg, which splits at some point after fertilisation. As a very rough guide, the embryo can split up to about fifteen days after fertilisation (medical complications sadly become more likely in cases where the split happens at the later end of that time frame). Some of you can probably see where this is going.

If an embryo at the point of fertilisation carries the potential to split and grow into multiple humans, then only three possible realities can exist:

  1. Whatever constitutes a human life cannot possibly exist within an embryo until some point after it is no longer capable of forming twins.
  2. Identical twins are half a human life each; triplets are a third of a human life each; and so forth, all because the embryo was already imbued with a human life.
  3. God makes some embryos human from the point of conception and makes some embryos human after they’ve split.

I would hope we can discard the second, because it’s so clearly ridiculous. If we think that a one-day-old embryo is an individual human life, then the rational corollary is that someone who kills one identical twin has committed one half of a murder.

The third may convince some people of faith, but it’s a really severe stretch, and for those without belief in a deity, it’s unbelievable. It can’t be a basis for policy in a secular system, or a usable argument anywhere outside of a religious discussion, because it’s completely untestable and completely without foundation — it has to be taken entirely on faith.

That leaves us with only one option. Because a just-fertilised embryo retains the potential for splitting and creating twins, it’s impossible for that embryo to already be imbued with a human life. Any argument based on that as a starting point is invalid, and so should be disregarded.




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Sebastian Marr

Sebastian Marr

Building a life that's Good Enough.

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