Evolution of complex traits in human populations

With the completion of the Human Genome Project and the increasing availability of dense panels with millions of genetic variants during the last decade, the identification of the fingerprint of classical positive selection events in the human genome is living a golden age of scrutiny. Nowadays, there is an ever-increasing number of methods developed to detect hard selective sweeps acting on de novo mutations within species. Despite the intrinsic problems underlying these methods (such as the lack of reproducibility, the influence of complex demographic history, and the presence of a large number of confounding factors), among different human populations, several genomic regions have been shown to be undergoing selective pressures. These discoveries are providing further understanding of the microevolution and microadaptation of our species. However, most phenotypes are of complex nature and arising from the frequently intricate demographic history of humankind. Therefore, most of the genetic variants that could have played an adaptive role in the past can be expected to have intermediate frequencies in the present. Under these circumstances, tests for detecting hard selective sweeps acting on variants determining complex human traits are underpowered, requiring new approaches for identifying positive polygenic adaptation. Here, we provide a succinct review of the current status of the field of evolutionary selection and describe the methodology we used to study the evolution of bone mineral density (BMD), and human stature as illustration of polygenic adaptation in humans.

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