Nicholas D. Kristof
One of the most profound and layered questions raised by recent genetic advances is this: Do we as a species still want babies born with genetic disabilities?

Science is scoring great successes in combating the 7,000 genetic ailments that can strike our children — and that sounds great. Yet it's difficult to draw a line where we stop "improving" our species. Many disability activists argue that we're moving toward a new eugenics, and I'm afraid that they could be right.

The first step toward upgrading our descendants will come in the treatment of disabilities because the benefits are so obvious. And so I sat down here in London with an expert on disability and genetics, someone whose struggle with the issue is not just scholarly but also personal — to me as well as him.

It all began when my British great-uncle, Sir Geoffrey Shakespeare, had a son, William. That's right: he became Sir William Shakespeare. (We in the family have always claimed to be related to the Bard as descendants of his cousin Humphrey Shakespeare; it's a coincidence that...