predictable. This unpredictability is partially responsible for changes in the brain. Promiscuous ma

predictable. This unpredictability is partially responsible for changes in the brain. Promiscuous mating systems demand more flexibility, creativity and out of the box thinking. The anthropologist Steve Gaulin explored the idea that a species’ mating system is directly related to its capacity to think. Gaulin started by looking at two closely related species of voles, one monogamous and the other polygynous. In the polygynous vole, males typically mate with multiple females. To achieve this kind of mating success, males have large territories that encompass many smaller female territories. In the monogamous species, the male and female share the same territory, with mating restricted to the couple. These differences in mating system and space usage have two direct consequences: relative to the monogamous male vole, the polygynous male vole must travel much further in a day than the females and must recall where the female territories are located. For a polygynous male vole, mating success depends on long day trips, visiting each of the female territories. For the monogamous male vole, there are no physical or memory challenges as the female is virtually always nearby. Given the costs to a polygynous male vole of forgetting where the females live, there should be strong selection on the memory system. Gaulin confirmed this prediction by showing that polygynous male voles outcompete females of their species in a maze running competition, and also have larger memory systems than females. In the monogamous vole, there are no sex differences in maze running or memory. Gaulin’s work provides a gorgeous example of how evolutionary pressures can act on the brain to create differences in psychological capacity. Other examples abound, including evidence that fruit eaters have larger brains than leaf eaters, primates living in large social groups have larger frontal lobes than those living in smaller groups, and bats living in open habitats have smaller brains than those living in complex closed habitats. In each case, a particular ecological or social pressure — finding ripe fruit, updating the status of numerous social relationships, avoiding obstacles while in flight — sculpts differences in brain anatomy and function. Some of these pressures favor extreme specialization and myopia, whereas others favor a broader vision. Relative to every healthy member of our species, all other animals have tunnel vision. When our ancestors began to migrate out of Africa, the diversity of environments and social opportunities favored generalists with a broad and flexible vision. To appreciate the significance of the human revolution in brain engineering, consider three cases of myopic, but highly adaptive intelligence in other animals, cases that lack the signature of intellectual promiscuity; these cases are of particular interest because they represent the kinds of examples that caused Darwin to doubt the beneficence of God, to reflect upon the cruelty of nature, and to ponder the problem of evil: * The wasp Ampulex compressa tackles a specific species of cockroach, inserts a first stinger into its body to cause leg paralysis and eliminate fighting, then a second Hauser Chapter 1. Nature’s secrets 27 HOUSE_OVERSIGHT_012773