The Symbionts

As the epochs passed, the two species molded one another to form a well-integrated union. The little arachnoid, no bigger than a chimpanzee, rode in a snug hollow behind the great "fish's" skull, his back being stream-lined with the contours of the larger creature. The tentacles of the ichthyoid were specialized for large-scale manipulation, those of the arachnoid for minute work. A biochemical interdependence also evolved. Through a membrane in the ichthyoid's pouch an exchange of endocrine ...

 Sexual Selection in the Wodaabe Tribe

Perhaps human aesthetics emerged through runaway sexual selection, with aesthetic tastes evolving as part of female mate choice. In this view, some female hominids just happened to have certain tastes concerning male ornaments. The artists best able to fulfill these tastes inseminated more aesthetic groupies and sired more offspring, who inherited both their artistic talent and their mothers' aesthetic tastes. Something like this still happens among the Wodaabe people (also known as the Boro...

 Evidence of Sexual Selection in Humans

By primate standards, humans look strange, even after we step out of our sport utility vehicles. Compared with other apes, we have less hair on our bodies, more on our heads, whiter eyes, longer noses, fuller lips, more expressive faces, and more dextrous hands. In most species, sexual ornaments like long head hair, hairless skin, and full lips would have evolved only in males, because females would have been the choosy sex. Males have few incentives to reject any female mates. The fact that ...

 Barriers that Keep Different Species from Interbreeding

What keeps members of two related species from mating with each other? There are many different reproductive barriers. Species might not interbreed simply because their mating or flowering seasons don’t overlap. Some corals, for example, reproduce only one night a year, spewing out masses of eggs and sperm into the sea over a several-hour period. Closely related species living in the same area remain distinct because their peak spawning periods are several hours apart, preventing eggs of on...

 Mating Strategies of Males and Females

A vivid demonstration of this difference can be seen by looking up the record number of children sired by a human female versus a male. If you were to guess the maximum number of children that a woman could produce in a lifetime, you’d probably say around fifteen. Guess again. The Guinness Book of World Records gives the “official” record number of children for a woman as sixty-nine, produced by an eighteenth century Russian peasant. In twenty-seven pregnancies between 1725 and 1745, sh...