(Page 304 from Shadows of Forgotten Ancestors by Carl Sagan and Ann Druyan.)

By human standards chimp sexual life is a perpetual open air orgy - compulsive, never-ending, and always with the male grasping the female from behind. The average copulation rate is one or two an hour. Every hour. For each mature chimp. In estrus, of course, it's more. When the females are ovulating and able to be impregnated, their vulvas and allied nether parts swell extravagantly and turn bright pink. In estrus, they're walking sexual advertisements, and are then far more alluring. Because estrous periods are to some degree synchronized, there are times when a chimpanzee group is a sea of bobbing, compliant, soliciting swollen red rumps. Olfactory cues also signal their sexual availability. In marginal cases a passing male, unable to determine just by looking if she's ovulating, may simply insert his finger into her vulva and take a sniff.

Chimpanzee sex isn't a long and drawn-out business. Maybe eight or nine thrusts, each taking less than a second, and they're done. The males have, by human standards, impressive recovery rates, including documented sequences of many ejaculations at five-minute intervals. Females in estrus are especially attractive in the early morning, probably because of the long and stressful celibacy imposed on the males by the necessity of having to sleep at night. As a kind of community property for the males, she may be taken every ten minutes by one male after another through mid-morning, by which time they may tire a little....

(Page 305 from Shadows of Forgotten Ancestors by Carl Sagan and Ann Druyan.)

Despite their apparently unrestrained sexual behavior, chimps get jealous. A male who rejected the solicitation of a female in estrus, but instead copulated with her daughter, was slapped in the face by the outraged mother. Cruising migrant females from the next territory are threatened or attacked by the local females - especially if the visitors go so far as to groom with one of the resident males. The male may also blaze with sexual jealousy over a particular female's behavior - but, almost without exception, only when she is vividly pink and swollen and able to conceive. High - ranking males will then chase away aroused lower - ranking males. Although it's unlikely he's thought this out, his motive, it seems very clear, is to monopolize her around the time of ovulation so that no one but he can father her children. As far as he's concerned, the rest of the time she can do as she pleases.

Possessiveness is hard to maintain, though, at the core of the territory where the chimp population density is high. Even the most vigilant and high-ranking males will be distracted - by hunting, say, or challenges from lower ranks, or insufficient deference, or by grooming, or by the necessity of adjudicating disputes. And during such an intervention - it may last only a few minutes - other males, patiently awaiting their chance, pounce on the off - limits female, especially if she's in estrus. Kleptogamy is on their minds. In zoos a female will, as soon as the alpha male is removed from her cage, present herself to lower - ranking males, even if this requires adroit positioning so the act can be performed through the bars of two adjacent cages. Both in the wild and in captivity, when the cuckolded male discovers what has happened, he attacks the female. Perhaps he knows that she was all too willing. Besides, it's much safer than attacking a rival male....

(Pages 314-315 from Shadows of Forgotten Ancestors by Carl Sagan and Ann Druyan.)

Chimpanzee society has an identifiable set of rules that most of it's members live by. They submit to those of higher rank. Females defer to males. They cherish their parents. They care for their young. They have a kind of patriotism, and defend the group against outsiders. They share food. They abhor incest. But they have, so far as is known, no lawgivers. There are no stone tablets, no sacred books in which a code of conduct is laid out. Nevertheless, there is something like a code of ethics and morals operating among them - one that many human societies would find recognizable and, as far as it goes, congenial....