Take height, for example. We know that tall parents have tall kids, but if you start looking for specific segments of DNA, you'll find over a thousand, none of which contribute more than a millimeter. The top 180 genetic markers still only account for 10 to 12 percent of the height variation from person to person. The rest of the story refuses to be pinned down. Brilliant people have spent years staring at these numbers, unable to sort them into any kind of rational order, even though to the untrained eye, there seems to be no mystery at all. Tall mom, tall dad: tall kid. But the closer we look, the less we understand.

Misha Angrist defends genome testing against Brandom's critique: