The Elephant in the Brain: Hidden Motives in Everyday Life

by Kevin Simler

These bowers serve only a single purpose: they’re built by the males to attract females. Crucially, they aren’t used by the females for laying eggs and raising young. After mating with a male, the female flies off to build her own (much smaller) cup-shaped nest up in a tree, and she raises her chicks entirely on her own, without any help from her mate. From the perspective of the female, then, the male bowerbird exists only to provide his half of the genome. This may seem like a waste. Why doesn’t he help raise his chicks, like the males of so many other bird species? But in fact, the bowerbird male provides more than just cheap sperm; crucially, he provides battle-tested sperm. Sperm that comes with a seal of approval from Mother Nature, certifying that the male in question is physically and (by implication) genetically fit. To construct and decorate a bower, a male must spend most of his free time scouring the forest for materials and arranging them meticulously into place. When his ornaments fade, he must collect new ones. He also needs to defend his bower against attack by his rivals, who are keen to sabotage his structure and steal his more impressive ornaments.19 “During the breeding season,” writes Miller, “males spend virtually all day, every day, building and maintaining their bowers.” The reward for all this effort is more mating opportunities. A successful male bowerbird can mate with as many as 30 females in a single mating season.20 The flip side, of course, i...