Marriage and Civilization

5 million years ago, the East African climate grew drier and the tropical forest receded, leaving treeless patches that eventually opened into the current vast savannas. Onto these open grasslands ventured our common ancestors who, if they were not identical to the chimpanzees of today, were much more chimp than they were human. Recent research suggests that they may have first survived in this sparse environment by digging roots deep out of the ground and that the sticks they used for this task may have been the first human “tool.” They were only about three feet tall, no bigger than today’s baboons.

What differentiates gibbon couples from human beings is that they are purely antisocial. They do not want other couples around. As they settle down to raise offspring, their songs become duets. These gibbon duets serve a very distinct purpose. They warn other males and females out of their territory.

They are purely monogamous. Gibbons court each other by singing eerie, high-pitched songs that can be heard half a mile away. If a male and female like each other’s song, they rendezvous in the forest, do a brief mating dance, and then copulate up to five hundred times over the next forty-eight to seventy-two hours, forming a tight sexual bond. (An immediate period of intense sexual abandon is what characterizes all monogamous species.)