My friends Edd and Simon have made some good points in criticism of my earlier post citing Christian feminist Frederica Matthewes-Green which made me realise I owe a more careful explanation of why I think that embryos should be treated as human beings to whom our general belief that we should not arbitrarily end human life applies. That was the presupposition of the post, which I shall try and defend here.
Conception is the beginning of something. Before conception, sperm and eggs do not become anything else. They just are what they are. So their meeting at conception changes them, and begins something. The only really relevant question is, what begins? Is it the beginning of human life as we commonly recognise it in one another (in which case its arbitrary ending could not be justified), or only the beginning of something which will subsequently become human life? (Even if it were the latter, it would still not be at all clear that it would be acceptable to destroy something that if left undisturbed would become human life.)