people from breeding, but by allowing them to breed, safe in the knowledge that they won't pass on painful conditions. Still, recent analyses of the human genome reveal a huge number of rare-and thus probably fairly new-mutations. One study, by John Novembre of the University of California, Los Angeles, and his colleagues, looked at 202 genes in 14,002 people and found one genetic variant in somebody every 17 letters of DNA code, much more than expected. "Our results suggest there are many, many places in the genome where one individual, or a few individuals, have something different," said Dr. Novembre . Another team, led by Joshua Akey of the University of Washington, studied 1,351 people of European and 1,088 of African ancestry, sequencing 15,585 genes and locating more than a half million single-letter DNA variations. People of African descent had twice as many new mutations as people of European descent, or 762 versus 382. Dr. Akey blames the population explosion of the past 5,000 years for this increase. Not only does a larger population allow more variants; it also implies less severe selection against mildly disadvantageous genes. So we're evolving as a species toward greater individual (rather than racial) genetic diversity. But this isn't what most people mean when they ask if evolution has stopped. Mainly they seem to mean: "Has brain size stopped increasing?" For a process that takes millions of years, any answer about a particular instant in time is close to meaningless. Nonetheless, the short answer is