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 this column is written in iambic pentameter.)

William was born with a genetic mutation that results in achondroplasia, a kind of dwarfism. William became a fine doctor (his short stature gave him a rapport with child patients), and his eldest son, my cousin Tom, was also born with achondroplasia. And Tom in turn has a daughter with achondroplasia as well.

Tom Shakespeare inherited the title and is formally Sir Thomas (which mortifies him), as well as a leading scholar on genetics and disability. As we sat down at a London coffee shop to talk about these issues, Tom attracted attention because he's not only the shortest person around but also the most self-confident, charming and funky, with earrings and tremendous presence.

"Society sees disability as the worst thing that can happen," Tom says. "It's one thing that can happen, but not the worst." All in all, he says, he's had more opportunities than if he had been born without a disability but into a poor family.

Tom says many disabled people feel threatened by genetic advances and are hurt by cheerful talk about engineering a world without people like them. "That's very difficult for disabled people," Tom says. "To hear people discuss a world in which you don't exist can be very hurtful."

"People ask me all the time, `Wouldn't you rather have been not short?' But that's almost like saying, `Wouldn't you rather have not been born?' "

Yet Tom notes that his own views have also evolved, and he struggled with the question of whether he would have another child with his same condition. Every father wants a child like himself, yet also a child with every advantage. In the end, he says, he will not have more children, partly because of the risk of disability.

If that's a knotty question, so is the broader one we face as a species. I disagree with those disability leaders who oppose strong efforts to combat genetic diseases. But I think they're right to ring alarm bells. The problem is that it may eventually become possible not just to cull embryos associated with dwarfism, but also to screen out baldness, pug noses or homosexuality, or even to choose the embryo most likely to get into Yale.

My guess is that germ-line gene therapy will arrive a bit further down the road, initially to fix "bad genes" that cause disease, and then moving on to enhance intelligence and performance. I'm afraid we may be slipping, without any conscious decision or even awareness of the implications, toward a future in which we will hugely accelerate our own evolution, in which our descendants quickly diverge from all that has been human for 200,000 years.

Bill McKibben, in his cautionary new book about genetic science, "Enough," articulates the dangers as he recalls a childhood friend, Kathy, who died of cystic fibrosis:

"Why not at least let the germ-line engineers go to work on the Kathys of the world? The harm is not to the patient but to the world in which she lives. As even proponents acknowledge, the line between repair and enhancement is too murky to be meaningful. Soon you're headed toward a world where Kathy's lungs work fine, but where her goodness, her kindness, don't mean what they did. Where someone's souping up her brains or regulating her temper, not just clearing up her mucus."