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 the UCL Genetics 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 adapted to it.
Genetic adaptation to new environments has hold an important role during human evolution. In addition human migration to colder climates and with less incident of sunlight, had adapted consequences for pigmentation or metabolic traits, likewise the changes in the subsistence strategies, for instance, after the advent of agriculture, a lot for both the establishment of larger and connected social groups, and for the availability of novel sources of food, with a notable impact at the metabolism level. Finally, the population expansions and 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 raised the question of to what extents 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 regions showing unusual patterns of allele frequency, haplotype diversity, or allelic differentiation between populations. Here in this table, I think coworkers collected some of the well-established examples of genes targeted by natural selection. Functionality has been somehow validated by in vitro or in vivo experiments. A decreased in melanin pigmentation in Europeans and a decrease in hemoglobin concentration in Tibetans and Ethiopians probably reflect genetic adaptation to certain environmental conditions, namely, the exposure to reduced UV radiations, and the hypoxia to high altitude. This persistence is one of the most notable examples of genetic adaptation to diet, with the polymorphism promoting the expression of the gene, encoding the enzyme lactase being at high frequency in European populations, and almost absent as well. Nevertheless, many biological pathways involved in the regulation of the immune system, and especially in modulation of a susceptibility to infectious disease, are enriched with signals of neo-neutral evolution, reflecting genetic adaptation to pathogen exposure. Indeed, several studies have confirmed the hypothesis whereby virtuous agents have exerted an exceptionally strong selective pressure on human population, and shaped the genetic diversity of melanocyte in the human genome.