No wonder that it is precisely the moralists of Western civilizations who are looking for evidence of monogamy's biological meaning - but more and more often find evidence to the contrary. Even animal species, which were considered prime examples of social and sexual twinning, often turn out to be highly polygamous on closer inspection. The most recent examples are the gibbon monkeys, who cultivate solid social relationships but are not averse to fast sex with strangers.
The gibbon example also shows that many do not always have to mean polygyny, as is usually the case with humans. In the animal kingdom in many species, both the males and the females are not squeamish when it comes to a short interlude with the attractive neighbors. "Gibbon females keep things going, " says anthropologist Ulrich Reichard of Southern Illinois University. Two sexual partners at the same time seem to be the rule rather than the exception. The monkeys signal their willingness to reproduce correspondingly conspicuously: their thick, swollen buttocks are also clearly visible from afar.
Others are more discreet, because jealousy is no stranger to wildlife: about 90 percent of all bird species, at least socially monogamous, so live together the offspring together - but this does not discourage occasional Schäferstündchen. "Blue-breasted females do everything they can to hide an infidelity, " explains Bart Kempenaers from the Max Planck Institute for Ornithology in Seewiesen in Upper Bavaria. Therefore, the early risers among the males have a particularly good chance of a little flirtation: The females visit the early singer in the early morning before their own partner awakens, and are back in time for breakfast together in the nest - a behavior that is very reminiscent of some human Schürzenjäger. display
But is this stress worth it? A clear answer to this question is so difficult, above all, because male and female organisms pursue opposing propagation strategies: producing a female egg costs significantly more energy than producing a large number of sperm. In the first place, females want to defend the result of a fertilized ovum and bind the males to themselves, while they achieve the best reproductive success by distributing their cheaply produced sperm to as many women as possible.
But what advantages do adults and infidelities offer to females? Bart Kempenaers has found a possible answer for Blaumeisen: her lovers come from more remote breeding grounds and thus differ in heredity more from the females than their social partners. And the greater the genetic diversity, the healthier and more efficient the boys are: "They grow better and have more offspring later, " explains the bird scientist in "bild der wissenschaft. The same seems to apply to Alpine Marmots. In the case of blue tits, the females even gain the advantage thus gained: they influence the order when laying eggs, so that the cubs of foreign males first hatch and thus receive a great deal of attention. How the females do that is still unclear.
In the white-hand gibbons, the males are partly to blame for the infidelity of their partners: they tend to kill the offspring of other females. The females protect themselves from this by copulating with so many males that they simply lose track: "The females cause insecurity. To their advantage, "explains anthropologist Ulrich Reichard, because so the males run the risk of killing their own offspring - and prefer to renounce the infanticide.
In their sexual behavior, people rely on a compromise solution: "We usually maintain a serial monogamy, " explains evolutionary biologist David Barash from the University of Wisconsin. So man and woman stay together at least until the offspring is out of the woods. However, men in particular often look for a new, younger partner. But although Barash's view of monogamy is clearly not in the nature of man, there are biological mechanisms that foster monogamous relationships: So-called love hormones such as oxytocin or vasopressin strengthen the sense of belonging and well-being Pair relationships one more, others less.By ddp correspondent Masha Schacht