One of our readers asked:
I have read that occasionally if a zygote splits, it will sometimes join back together instead of going on to form twins. This rises an interesting, and currently unanswered question: since a human being is indivisible, how can you say that the split zygote has two souls if it splits and then rejoins? It would be illogical to say that if a zygote should split, but then rejoins that there were two souls which then became one.
I have no problem with the statement that human life begins at fertilization. But since fertilization is, as described in the article, a process, do we say that human life, or a human person, begins at fertilization? We talk about it like they are the same thing, but in order for the Church’s teaching to not be self-contradictory, they might be different. Otherwise, if a zygote, holding all the material of a human person, splits, then it’s two human persons. But what happens to that extra person if it rejoins? A zygote, split or unified, is definitely alive, but it would be weird to say that God is injecting a human soul into our bodies like a vaccine…just playing devil’s advocate here. You don’t have to agree with me, but somebody is going to need to get this clarified at some point.