The sexual imperative. Part 3, A time and a place.

The Sexual Imperative series explores the reasons for sexual and asexual reproduction in the insect, animal and human worlds, and concludes with a look at human sexuality. This episode looks at what triggers reproduction and why particular males and females are attracted to one another. The changing seasons and weather are signals to many animals and insects to mate. Palola worms reproduce according to the full moon and the horseshoe crab waits for high tide. In spring, many animals mate, including gazelles and golden jackals. Rain in the Arizona desert causes the spadefoot toad to come out of its underground burrow and mate. Other animals work to their own timings; some cicadas gestate for 17 years. Animals attract mates in various ways, whether by looks, as with Jackson's Widowbirds, or by a display of skill, as with weaver and bower birds. Different human cultures also mate for different reasons, with love being a main reason in the west.