Recent human adaptations

Human populations live in an extraordinary variety of different habitats: hot and cold, wet and dry; in forests, grasslands and tundra. Different human groups feed on a wide variety of food sources. For many populations, diets shifted further with the development of agriculture in the past 10,000 years. To what extent have these and other factors led to genetic adaptation?

¹Human populations differ in various phenotypes – observable characteristics that result from interactions between genes and the environment –, but ²scientific studies have shown that phenotypic differences have a genetic basis and are adaptive. For example, mammals that live in cold climates tend to have larger, rounder bodies and shorter limbs than members of the same or closely related species in warm climates. ³These patterns do appear to also hold in humans, implying that population movements into colder climates were accompanied by adaptation to larger, stockier body shape, presumably to improve thermal efficiency. At the other end of the spectrum is the pygmy phenotype that has evolved in rainforest populations in Africa, South-East Asia and South America. Research has suggested that ⁴this phenotype may be an adaptation to food limitations, high humidity or dense forest undergrowth.

Another impressive example of adaptation is provided by human populations living at high altitude, especially in the Himalayas and the Andes. Compared to related lowland populations, ⁵these high elevation populations show a group of physiological adaptations to low oxygen. These adaptations include markedly increased blood flow and oxygen delivery to the uterus during pregnancy, substantially reducing the risk of babies with low birthweight. ⁶Current evidence suggests that these differences are not simply the result of recent acclimation, but are at least partly genetic. If this is the case, then ⁷the adaptation must have occurred rapidly, because ⁸these high altitude regions were settled within the last 10,000 years.

⁹Skin pigmentation is perhaps the phenotype that varies most obviously among human populations. ¹⁰ Dark pigmentation is strongly associated with tropical climates, and the spread of prehistoric humans into northern latitudes was accompanied by a shift to lighter skin color. We now know of at least half a dozen different genes that affect skin, hair or eye pigmentation. In particular, the evolution of light skin color occurred largely in parallel in western Eurasia and east Asia, but we still know few of the relevant genes in east Asia. Adaptation to lighter pigmentation may have been motivated by a need to increase UV absorption for vitamin D synthesis at high latitudes or by sexual selection.

These are only a few cases of genetic adaptation. There are surely some – perhaps many – other ¹¹factors yet to be found.

(sciencedirect.com)

Human populations differ in various phenotypes¹

In relation to these phenotypes, scientists have reached the following conclusion: