Odd Couples: Extraordinary Differences between the Sexes in the Animal Kingdom
Daphne J. Fairbairn
Princeton University Press, 2013 ($27.95)

Biologists have long debated the specific traits that set humans apart from other animals: Is it self-awareness, or morality, or emotions? Recent research has cast doubt on each of these premises, but Odd Couples notes that we are exceptional in at least one respect: how we distinguish men from women. Throughout the animal world, it is far more common for males than for females to be petite and brightly colored. Fairbairn, a biologist at the University of California, Riverside, traces the evolutionary reasons behind these and other sexual differences, while exploring some extreme and fascinating examples. Cases include populations of elephant seals (above), in which large, aggressive males sexually harass harems of females, and of deep-sea anglerfishes, in which males live as tiny parasites permanently attached to the bellies of their large, predatory female partners. One constant across all species seems to be: there's no accounting for taste.