From a reader:

Jonah –
Yes, I’ve read POD, and I generally admire Derb (being of sour disposition,
myself).
Years ago, someone invited me to agree that a fertilized egg, by virtue of
having a complete DNA set and everything necessary to describe a human being,
was indeed a human being. That is hard to refute scientifically. But alas, it
fails to take into account that notions of what constitutes humanity precede
knowledge of sperm plus egg interaction, and precede knowledge of DNA.
Looking at it another way: We know that identical twins come from a single
fertilized egg. If it was a person before it split, then are the twins each
half-persons? Or, was it two persons before it split? On such rocks do strictly
scientific conceptions (intentional pun) founder.
More to the point: The DNA argument does not convince me, regardless of its
merits, even though I am not a supporter of the “right to choose.” And, if we
presume that the majority of American working scientists are “pro-choice,” then
it does not convince them, either. One either has to suppose that the
scientists are hard-headed irrationalists, or suppose that the argument cannot
be won by science.
The strength of Ramesh’s book was in deconstructing many “historical” arguments
in support of abortion, and in exposing the shaky foundations of many tales
represented as facts. But ultimately, I do not believe that any degree of
rationalism will win the debate, either way.