Judging from fossils and studies on DNA, the common ancestor of humans, chimpanzees, and bonobos lived roughly six million years ago. Hominids inherited the genome of that ancestor, and over time it evolved into the human genome. A major force driving that change was natural selection: a mutant gene that allowed hominids to produce more descendants than other versions of the gene became more common over time. Now that scientists can compare the genomes of humans, chimpanzees, mice, and other animals, they can pinpoint some of the genes that underwent particularly strong natural selection since the dawn of hominids. You might think that at the top of the list the scientists would put genes involved in the things that