Where Is Human Evolution Heading?

The next step: children with genes from three parents. In the late 1990s, IVF clinics started injecting cytoplasm from younger women's eggs into those of older women, in an effort to increase the odds of pregnancy. About 30 babies have been born worldwide as a result, and those children carry genes from both women. But that rejiggering of the human germline was almost inadvertent. Scientists are now intentionally making that mix. Earlier this year, researchers at Newcastle University in England deliberately created human embryos that had DNA from one father and two mothers, in order to avoid the risk of a mitochondrial disease from the original mother.

But it's too early to lie awake worrying that genetically manipulated superkids are going to ace your grandkids out of varsity soccer, says Thomas Murray, a bioethicist and president of the Hastings Center. "Our capacity to do these kinds of intentional designs is vastly overrated." But, he says, it's not too early to start thinking about what's really important about being a parent. The traits that people most value, Murray says—being smart, being kind, being a successful competitor—are the ones least likely to be determined by a few tweakable genes. For that kind of control over the next generation, it still takes good old-fashioned nurturing, teaching, and love.