Natural selection and human adaptability
Testing multiple models of natural selection is become possible thanks to the most up-to-date experimental approaches for characterizing genomic variability of human populations, as well as to the methodological improvements recently achieved in detection of the signatures left by natural selection on the human genome. This enables us to exhaustively investigate the adaptive processes occurred in the recent human evolutionary history in response to a range of selective pressures.
Following H. sapiens diffusion out of Africa, occupation of a range of different environments has prompted ecological and cultural changes that introduced novel challenges to our organism due to selective pressures different with respect to those that have shaped the evolution of our African ancestors. This has driven a number of local adaptive events in response to peculiar climate conditions, nutritional resources and/or pathogens’ landscapes, which are mediated by the action of natural selection on the gene pool of the targeted populations. Despite a number of phenotypic features (e.g. skin pigmentation, height, lactase persistence, adaptation to hypobaric hypoxia, etc.) that are advantageous in a given environment has been long investigated, the genetic bases of most complex adaptive traits have been not elucidated so far.
Recent improvements in high-throughput genotyping and massive parallel sequencing technologies, coupled with the development of new statistical methods to test for the occurrence also of weak selective events on multiple genes and/or on standing variation have provided new opportunities to effectively search for signatures of the action of natural selection on the human genome. It is thus possible to identify variants with single small effect on the phenotype, but concurrently contributing to polygenic adaptation. This promises to represent a milestone in such a research filed because this typology of selection is supposed to have played a substantial role in shaping the evolution of human adaptability to different environmental and cultural contexts.
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