Evolution is a slow process, and it is therefore seldom that we are able to directly observe genetic changes that have been selected for in our lifetime. Killifish is the name of several families of fish that inhabit lakes, streams, and rivers around the world. In the Atlantic ocean, we know that some killifish populations residing in highly polluted habitats have undergone rapid evolution to this toxic environment. This is the case for Fundulus heteroclitus, and a new research study published in the journal Science sequenced ~50 individuals from eight populations of F. heteroclitus. Two populations were sequenced to 7-fold coverage and the remaining populations to 0.6-fold coverage. The authors used a genomic window of 5 kb showing Tajima’s D to identify regions associated with pollution tolerance. Interestingly, there were shared regions of showing signals of selection, which is likely to reflect convergent evolution. Some of these genes encode genes involved in the aryl hydro-carbon receptor signaling pathway. Notably, a member of the large and polymorphic cytochrome P450 family (CYP1A) – involved in the transformation of xenobiotica – is present within these regions.