Does natural selection apply to humans? The physiology of the Bajau people of Indonesia suggests that at least in some cases the answer to this question is yes. The Bajau make their living off the sea, and are renowned for their diving ability, routinely free diving (without scuba gear) hundreds of feet deep and holding their breath for up to thirteen minutes. This ability seems to be enabled by exceptionally large spleens. The spleen releases oxygen-rich red blood cells when breathing is restricted. Genetic and other evidence suggests that the spleens may be a result of selection.
Thanks to modern medicine, technology, and modern economies, some people argue that selective pressure no longer applies to humans, at least in the developed world. People, and their genes, that might once have died in infancy from an illness or infection can now reach maturity and have as many children as anyone else. But biologist Michael Balter suggests that evolution never stops, even for modern humans. This is especially true in parts of the developing world, where disease and other pressures still do threaten survival. For example, there is evidence that genetic resistance to certain diseases such as malaria exists in vulnerable populations.
In populations like the Buriat people of Siberia, whose broad faces might be an adaptation to cold climates, measurable physical changes seem to have been driven by selection. More commonly, scientists studying evolution in humans look to genetics. Anthropologist Sandra Wilde and colleagues examined the frequency pattern of three specific genes associated with skin pigmentation over the past five millenia. The pattern suggested that selection has favored lighter skin, hair, and eye color in Northeastern Europe. The body produces vitamin D in response to sunlight. Lighter pigmentation eases vitamin D production where sunlight is seasonally reduced at high latitudes.
In many of these cases, the human penchant for settlement and agriculture have driven these changes. Malaria, for example, only became a problem when clearing forests left pools of water for mosquitos to breed; it is around that time, thousands of years ago, that resistance genes began to be more common. The selection favoring light pigmentation also began after humans began switching to agriculture, and their diet started to contain less vitamin D-rich game and fish. The gene for lactose tolerance that allows adults to digest dairy products also arose as a result of agriculture and livestock husbandry.
In essence, our modern life, rather than halting evolution, is driving it into new paths.