Topology of viral evolution

Evolution is mediated not only by random mutations over a number of generations (vertical evolution), but also through the mixture of genomic material between individuals of different lineages (horizontal evolution). The standard evolutionary representation, the phylogenetic tree, faithfully represents the former but not the latter scenario. Although many elaborations have been developed to address this issue, there is still no agreed-upon method of incorporating both vertical and horizontal evolution. Here, we present an alternative strategy based on algebraic topology to study evolution. This method extends beyond the limits of a tree to capture directly even complex horizontal exchanges between multiple parental strains, as well as uncover broader reticulate patterns, including the segregation of segments during reassortment.