Discovering human history from stomach bacteria

Abstract

Recent analyses of human pathogens have revealed that their evolutionary histories are congruent with the hypothesized pattern of ancient and modern human population migrations. Phylogenetic trees of strains of the bacterium Helicobacter pylori and the polyoma JC virus taken from geographically diverse groups of human beings correlate closely with relationships of the populations in which they are found.

Figure 1

The relationships between human populations, as calculated from H. pylori found in stomachs and from mitochondrial DNA data. (a) Relationships between modern subpopulations of H. pylori [5]. Each subpopulation is represented by a circle with a diameter proportional to the genetic diversity within it. The centres of the circles are joined by a phylogenetic tree showing the relationships between the four subpopulations. Bacteria in each subpopulation are found predominantly in people who originate from the regions shown. (b) A population-level phylogenetic tree of the H. pylori geographic subpopulations shown in (a). (c) A median-joining network of human populations derived from mitochondrial DNA [14]. Such a network shows alternative potential evolutionary relationships between clusters. Each circle represents a cluster of mitochondrial types with a diameter proportional to the frequency of that type within the subpopulations. All non-African populations are derived from one African lineage; the network of relationships within this lineage is magnified (top). (a,b) Adapted from [5]; (c) adapted from [14].

Figure 2

A map of the pattern of expansion and migration of modern humans throughout the world, derived from studies of mitochondrial DNA and Y chromosomes [14,15,17,18]. Numbers indicate the approximate time (in years before the present) when modern humans first appeared in the indicated region.

Figure 3

Relationships of human polyoma JC virus (JCV) subtypes found in humans from different parts of the world [7]. Letters refer to individual subtypes. (a) The hypothesized pattern of spread of JCV subtypes through the world (excluding the Americas); (b) an inferred phylogeny of JCV subtypes, assuming an African origin for the virus. Adapted from [7].