The genomics of adaptation, divergence and speciation: a congealing theory.

In this issue, Flaxman et al. () report the results of sophisticated whole-genome simulations of speciation with gene flow, enhancing our understanding of the process by building on previous single-locus, multilocus and analytical works. Their findings provide us with new insights about how genomes can diverge and the importance of statistical and chromosomal linkage in facilitating reproductive isolation. The authors characterize the conditions under which, even with high gene flow and weak divergent selection, reproductive isolation between populations can occur due to the emergent stochastic process of genomewide congealing, where numerous statistically or physically linked loci of small effect allow selection to limit effective migration rates. The initial congealing event can occur within a broad range conditions, and once initiated, the self-reinforcing process leads to rapid divergence and ultimately two reproductively isolated populations. Flaxman et al.'s () work is a valuable contribution to our understanding of speciation with gene flow and in making a more predictive field of evolutionary genomics and speciation.