  A good place to begin is with a simple, yet realistic, example. In research carried out over many years and combining painstaking field work and laboratory experimentation, John Endler was able to demonstrate that the color patterns of males in the guppy populations he was studying in rivers feeding into the southern Caribbean were a consequence of a balance between mate selection and predator selection. To take one startling example, he was able to test and confirm a hypothesis that a group of males, with a color pattern that matched that of the pebbles on the bottoms of the streams and ponds they populated except for bright red spots, have that pattern because a common predator in those populations, a prawn, is color blind for red. Red spots did not put their possessors at a selective disadvantage, and were attractors for mates (Endler 1983, 173–190). We may refer to this pattern of coloration as a complex adaptation that serves the functions of predator avoidance and mate attraction.  But what role do those functions play in explaining why it is that the males in this population have the coloration they do?