Why Are We Discussing This?

When does life begin?

Here:

. . . members of the media were mostly interested in my finding that 96% of the 5,577 biologists who responded to me affirmed the view that a human life begins at fertilization.

It was the reporting of this view—that human zygotes, embryos, and fetuses are biological humans—that created such a strong backlash. 

Why is this being discussed? There is simply no reasonable question as to when an individual biologically human life begins.  It begins at fertilization. That is not to say (but neither is it to deny) that normative personhood begins at conception.  That is a further and much more difficult question. It  is the question about when a biologically human individual becomes a rights-possessor, where one of the rights is the right to life. 

Consider a fetus, using the term in the narrow sense as above. If it is the offspring of biologically human parents, then, self-evidently,  it is biologically human. What else could it be? Bovine? Porcine? Lupine?  Not even Wolfman Jack was lupine in his pre-natal existence.

You don't need to be a biologist to know that biologically human parents have biologically human offspring. You also don't need to be a biologist to know that in the typical case human fetuses are living organisms. What else would they be? Dead? Is every birth still birth?  You would have to be profoundly ignorant to think that a biologically human being begins to live when it takes its first breath.  One does not come into existence as a human individual when one is born.

Don't ask: When does life begin?  This question is insufficiently specific to be tractable.  It is ambiguous as between phylogeny and ontogeny, and as between human and non-human.  Presumably you are not asking when life first appeared on Earth. Nor are you asking when human life first appeared on Earth. Define your terms and formulate the question precisely. These are interesting questions, but they are not relevant to the abortion debate.

Ask this: When does an individual biologically human life begin?  The answer is clear: at conception. There is nothing to discuss and you don't need no stinkin' survey of 5, 557 biologists to know the answer! (And what's with the dissenting 4%?)

Ask this: When does an individual biologically human life first acquire rights? There is much to discuss here, and the answer is not obvious.

See the entries in my Abortion category for my answer to the last question, especially those having to do with the Potentiality Argument.