A comprehensive scan of the human genome finds that hundreds of our genes have undergone positive natural selection during the past 10,000 years of human evolution.
Genes are the instructions organisms use to make proteins. They are encoded in genetic material, usually DNA, and some come in different versions, called “alleles." Positive natural selection occurs when one allele is favored over another due to changes in the environment.
Researchers from the University of Chicago analyzed the genomes of 209 unrelated individuals from three distinct human populations: East Asians, Europeans and Yorubans from Nigeria. Each population contained roughly 250 positively selected genes; however, most of the affected genes differed depending on the group.
“This study addresses the question 'Are humans still evolving?', and the answer is 'Absolutely,'" study team member Benjamin Voight told LiveScience.
Other studies have also reached the same conclusion.
Links to history
The new study links genetic changes to major events in the history of our species.
“There have been a lot of recent changes—the advent of agriculture, shifts in diet, new habitats, climatic changes—over the past 10,000 years," said Jonathan Pritchard, a human geneticist at the University of Chicago who led the study.
Many genes were found to be evolving in all three of the human populations studied. The specific functions of many of the genes are not known, but the researchers were able to separate them into broad categories. These categories include:
- Olfaction: the researchers found many genes important for taste and smell
- Reproduction: involved in things like sperm mobility and egg fertilization
- Increasing brain size
- Bone development and skeletal changes
- Carbohydrate metabolism: positive selection was observed for genes involved in breaking down mannose in Yorubans, sucrose in East Asians, and lactose for Europeans. (Mannose is a sweet secretion found in some trees and shrubs, sucrose is common table sugar, and lactose is a sugar found in milk.)
- Disease resistance and pathogen protection
- Metabolism of foreign compounds, such as exotic plant proteins or animal toxins
The researchers also found positive selection in four pigment genes important for lighter skin in Europeans that were not known before. Scientists think humans evolved lighter skin in Europe as an adaptation to less sunlight.
And in East Asians, they found strong evidence of positive selection in genes involved in the production of alcohol dehydrogenase (ADH), a protein necessary for breaking down alcohol. Many East Asians can't metabolize alcohol because they carry a mutation that prevents them from making ADH. The new finding suggests that the mutation may confer some currently unknown additional benefit.
The study, which used data collected by the International HapMap Project, is detailed in the March 7 issue of the journal Public Library of Science-Biology.
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