Sure Bill, a zygote is of course a human being - I state as much a few lines later. I should have been a bit more attentive while typing and clarified - a zygote will give rise to a child, adult etc., human if nothing intervenes.

Mrr: "As an aside, to me, a pregnancy is a woman's body part"
A pregnancy is not a body part. a pregnancy is a process whereby a new life grows inside its mother and is born (passes out of its mother's body).

I have heard this argument many times, about 'a woman having control over her body'. This ignores the fact that there are two lives in question. The new life growing within her is not simply an organ of the mother's body or a piece of waste. If it were so, denying a woman an abortiion would be as unreasonable as denying her laxatives if she were constipated. The fact that the unborn baby is a separate human being puts it in an altogether different category.

As for the twins - no, I don't think it is fratricide. What is happening is a natural process. One embryo gets more nourishment than the other and survives, but neither sets out to kill the other. If they did, it would be murder of course. Though at least froma legal standpoint one would have trouble prosecuting, as in the case of older children who murder.

The cell you described could at best be a possible potential human being in the same way a sperm cell is not the same thing as a new human being.

Correct me if I'm wrong, but even identical twins do not share the exact DNA. I seem to remember that however similar their appearance, ethy at least have separate finger prints. And no matter how close they are to each other, they both regard themselves as individuals.

I would be in favour of outlawing IVF that makes and discards zygotes, given that I see each zygote as a human. That might not be popular I know, but here now we have a problem where scientists want to use these zygotes (humans) for experiments, claiming they'd only be thrown out anyway. True, but if they hadn't been created in test tubes in the first place, there wouldn't be anything to 'throw out'.

This is an example of the failure of science to address moral issues. Clearly it cannot, since science is about finding out what makes the world tick, and seeing where it can take that knowledge further. But it's a bit like a boy pulling half the wings off a fly to see if it will fly more slowly: an interesting experiment, but one wonders should he be conducting it? That's why I say we need something more than empirical science to deal with moral and social questions.