Human pathogen-driven evolution

Published on March 18, 2015   44 min

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Hi, my name is Matteo Fumagalli, and I'm a research associate at UCL Genetic Institute, University College London. Today I'll be talking about how pathogens have exerted a strong selective pressure throughout human history, and how humans have genetically adopted to it.
Genetic adaptation to new environments has held an important role during human evolution. The ancient human migration to colder climates with less incident of sunlight had adaptive consequences for pigmentation or metabolic traits. Likewise, the changes in the subsistence strategies, for instance, after the advent of agriculture, allowed for both the establishment of larger and connected social groups, and for the availability of newer sources of food, with a notable impact at the metabolism level. And finally, the recent expansions in proximity to livestock, as well as recent human migrations and colonization of new habitats, enhanced the exposures to novel infective agents, and the spread of new diseases, imposing a strong selective pressure at the immune system level. These observations raise the question of to what extent these selective pressures have left a signature in the human genome.
Genome wide scans for signatures of natural selection in the human genome aimed at identifying the regions showing unusual pattens of allele frequency, adaptive diversity, or analytic differentiation between populations. So here in this table, Vitti and coworkers collected some of the well-established examples of genes targeted by natural selection. Its functionality has been somehow validated by in vitro or in vivo experiments. A decrease in melanin pigmentation in Europeans, and a decreased hemoglobin concentration in Tibetans and Ethiopians probably reflected a genetic adaptation to certain environmental conditions, namely the exposure to reduced UV radiation, and the hypoxia to high altitude. This persistence is one of the most notable examples of genetic adaptation to date, with the polymorphism promoting the expression of the gene encoding the enzyme lactase being at high frequency in Ethiopian populations, and almost absent elsewhere. Nevertheless, many biological pathways are involved in the regulation of the immune system, and especially in modulation of susceptibility to infectious disease are enriched with signals of known? natural evolution, reflecting genetic adaptation to pathogen exposure. Indeed, several studies have confirmed the hypothesis whereby infectious agents have exerted an exceptionally strong selective pressure on human population, and shaped the genetic diversity of many loci in the human genome.