First, Cochran and Harpending use recently mined genetic data to show that favorable new genes (such as the one for lactose tolerance) still sweep through human populations. Next, they argue that such “sweeps” have created vital differences among evolutionary subgroups. One chapter suggests that long-agricultural Europeans have developed stronger organizational and planning skills than nomadic sub-Saharan Africans. Other, equally contentious chapters address the intelligence of Ashkenazi Jews, and interbreeding between humans and Neanderthals. Cochran and Harpending’s conclusions may or may not pan out — some are more convincing than others — but their interlacing of genetics and anthropology is almost always enthralling.