To determine if newt toxicity and snake resistance had coevolved, Butch had to go back to the basics of natural selection. By this time (more than thirty years after he started the investigation as a graduate student), Butch had become Dr. Brodie and was investigating the snakes and newts with the help of his son, Dr. Edmund D. Brodie, III, as well as many other researchers and students.

Their first job was to show that natural selection could operate on both newt toxicity and snake resistance. And in order to do that, they had to demonstrate that the three requirements of natural selection — variation, heritability, and differential reproductive success (i.e., selection) — was true of both the newts and the snakes. For example, if some newts produced more toxin than others (variation), and if more toxic newts escaped their predators and survived longer to produce more offspring (differential reproductive success or selection) and if those offspring inherited their parents’ level of toxicity (heritability), over time the newts would evolve to be toxic through natural selection. But in order for natural selection to operate in that situation all three requirements must be met. Did the newts meet those requirements? Click on the “test it” links below to find out.