The Passaic River and Newark Bay in New Jersey are full of toxic pollutants, killing many fish and organisms in the area. However, one of the most diverse vertebrates, the Atlantic killifish, has managed to adapt to these conditions. Several independent populations of killifish have evolved different adaptations to the toxic environment. Biologist Diane Nacci with the Environmental Protection Agency (EPA) and other scientists compared 384 killifish genomes, finding that tolerance to this pollution is found on the aryl hydrocarbon receptor (AHR) signaling pathway for each of the populations, but that different nucleotide patterns were found in each one. An environment that would kill killifish without the mutation can house several different populations with slightly different mutations. Scientists believe that the ability for killifish to adapt quickly are due to very large populations, and therefore greater nucleotide diversity.
However, though some animal species have the capacity to adapt to large amounts of pollution and effects from climate change, that does not mean that all species are capable of that. It is likely that only a select few species will have the capacity to mutate or evolve resistance to human-induced effects such as pollution or accelerated climate change. On a different note, if the water is cleared up again, the killifish with the mutation for pollution resistance may not survive as well as killifish without the mutation, though by that point most if not all of the killifish without the pollution resistance in the area may have already gone extinct. It is very important to look at the grand scheme of things, and if people continue to contribute pollution and fossil fuels into the environment, species that are low in numbers are unlikely to develop a resistance and are likely to go extinct. Though this study gives clues into how natural selection operates under extreme conditions, people should not let the planet and its living creatures come to this point.