Andrew Whitehead, an environmental toxicologist at the University of California, Davis in the U.S. is intimately familiar with another striking example of how humans can drive rapid evolution in animals. In particular, he looks at a little fish called the killifish. “There are populations living in these radically human-altered estuaries, and these are environments that should be lethal to them,” he explains. Certain estuaries in the U.S. are full of chemical pollution, yet the fish are thriving. As Whitehead says, “Killifish from those sites are resistant to up to 8,000 times the normally lethal concentration of these chemicals.”