7 - Microbes as Tracers of Past Human Demography and Migrations

Abstract

Frequent bottlenecks and recent diversification result in relatively low levels of genetic diversity and population structure in modern humans, making inferences of their history difficult from classical genetic markers. To get around this drawback, pathogens, which have coevolved with humans and generally present a higher genetic diversity, can illuminate their host history. Following this idea, population structure of several microbes has been investigated by means of phylogenetic, coalescent, and Bayesian methods. However, the utility of such bugs as human tracers varied considerably according to the studied pathogen and targeted molecular markers. Indeed, the efficacy of inferring host history from a pathogen depends on certain life-history traits and genetic characteristics of the pathogen. Recent studies of three important human pathogens have been used to decipher both past and recent human migrations: Helicobacter pylori, which is nowadays the most studied pathogen in this context, Mycobacterium tuberculosis, and Mycobacterium leprae. In contrast, studies on population structure of viral species such as the human polyomavirus JCV displayed results somewhat dubious with respect to resolving human evolutionary history. In this chapter, the authors illustrate how pathogen population structure can be used to decipher human migrations and origins by documenting studies based on the pathogen species mentioned earlier.