Humans are a remarkably homogeneous species, with any two people, regardless of racial or ethnic group, being 99.9 percent identical at the genetic level. Still, the residual 0.1 percent translates to roughly three million spelling differences, with some conferring dramatically higher risk of Alzheimer's disease or breast cancer. Clearly, some DNA changes are unquestionably negative mutations, destroying the function of a crucial protein. It's easy to slip into speaking of deviations from an ''ideal'' genotype, although population genetics instead suggests the image of a genetic tapestry is closer to the mark. These are serious goals, not to be lightly dismissed.
Safety is, of course, a major concern.
Given the subtleties of human physiology, quick genetic fixes are likely to do more harm than good. And the prospect of a ''product recall'' from the human gene pool is too surreal to contemplate. But there will come a time when we can do such things safely, and it's not too soon to ask whether we should. If we cross that fateful threshold, I don't see how we can ever return. I part company from some of my colleagues here.