Are Homo Sapiens naturally monogamous or polygamous


The hot, humid air of the Thai rainforest lays on Ulrich Reichard's face as he lectures at 6 o'clock in the morning about marriage for three - under Gibbons. The little great apes were long considered sexually monogamous "until we proved otherwise". The primatologist is just about to dig deep when loud singing from the left drowns out the sound of raindrops falling from the leaves. “That's Hima, a female,” he says quickly and then seems to sink silently into Hima's aria. Bizarre, as the researcher stands in the Khao Yai National Park 150 kilometers east of Bangkok, his body in complete "combat gear" including camouflage colors and gauntlets over his boots. How he sways in the melody and raises and lowers his arms with his eyes closed, as if he were directing the wild creature like a maestro. Seconds later, Reichard returns to the real world: “Hima maintains a ménage-à-trois.” One female, two male partners?

It's not that unusual. “We rarely find sexual monogamy in the animal kingdom,” explains the scientist, currently employed at the American “Southern Illinois University”. Whether male or female: Most of the time, the animals don't take it that seriously when it comes to loyalty - even if they live in socially monogamous boxes of two, i.e. for a long time with a steady partner like most bird species. Not to mention, if they roam polygamous like most mammalian species including primates. Sexual monogamy also seems to be the exception rather than the rule in the case of the upper primate, humans. “There are deep traces of polygamy in our genome,” sums up the geneticist Michael Hammer from the University of Tucson (USA) after his most recent studies. Nevertheless, monogamy can bring great advantages, finds US evolutionary psychologist David Barash from the University of Wisconsin - and sums it up in a Solomonic way: “Our biology does not rule out monogamy. We have the choice! ”The fact that the little ape Gibbon has left the manageable circle of lifelong loyalists disturbs those contemporaries who are looking for role models for human virtues in the animal kingdom. "Like the swans, the gibbons had to serve as a prime example of social and sexual monogamy," complains Reichard. Out of necessity, because moralists would have preferred to rely on the behavior of chimpanzees or gorillas. But these two great ape species in particular do not even consider social monogamy, let alone sexual monogamy.


Many white-handed gibbon females in Khao Yai allow themselves to be charmed by two males with a firm bond - and, if urged, they also look for passable gibbon masters in the neighboring area. “They always have something going on,” says Reichard. The menage-à-trois plus infidelity testifies in a glaring way a trend that is emerging more and more clearly from hundreds of thousands of hours of field research worldwide: even animal ladies do "it" on the side, and not too scarcely. Take Hima, the gibbon blonde, who is now dueling with Claude, her primary partner, about 30 meters above us in the treetops. Her abdomen is thickly swollen: With this she shows interested candidates, even at great distances, that she is not averse to sex. During her entire cycle she copulated frequently with her second partner Nidhart, but far more often with her first choice Claude. Such observations challenge the theories that evolutionary biologists have come to love, such as this: Social (including sexual) monogamy is worthwhile for females because exclusive devotion ensures that the father will take care of the young. And that's what matters from an evolutionary point of view: The success of an animal is measured by the number of its viable offspring. For a father, however, social monogamy is more like a reproductive prison because it prevents him from inseminating several females with little effort.

In light of all of this, Hima takes a risk in allowing different men to mate. But in the love game of the white-hand gibbons, "it's more the females who set the rules," says Ulrich Reichard. By giving preference to the primary male, they arouse his interest in advocating for and protecting the young. Because child murder, committed by other male competitors, is widespread in harsh animal societies. But because the gibbon ladies have sex with several men, none of them can be sure whether they have accidentally killed their own child. “The females,” Reichard believes, “create insecurity. To your advantage."

The spectacle, instigated solely by the forces of evolution, succeeds because the gibbon men come to terms with each other. But, says Reichard: “They always look very carefully at what their peers are doing.” If a male pushes himself into a supposedly monogamous two-way relationship, the competitors sometimes fight brutally for dominance. Although this results in a winner, the loser often does not leave the couple - which the boss in the ring tolerates, presumably because the risk of continued aggression is greater than the risk of losing paternity to a rival. So the gibbons do it colorfully, without any secrecy.


Not so with birds: Bart Kempenaers knows his way around the game of blue tits. "The females do everything they can to hide an affair," says the director of the Max Planck Institute for Ornithology in Seewiesen in Upper Bavaria. Before the sun rises and the partner has woken up, they flutter into a distant area for a quickie. Without hesitation, they look for a singing male, copulate and rush back to their still sleeping partner. A few minutes - and the sex trip, including the flight there and back, is over. If you come out of the nest early as a male and start the enticing song, you increase your chances of having quick sex.

Around 90 percent of all bird species are socially monogamous. Both partners are much more necessary for the rearing of the tiny young than for mammals, where the mother breastfeeds the offspring. Sexually monogamous are no more than five to ten percent of the flying species. Even the swans are not as pure as their reputation. There are clutch of birds in which not a single young comes from the social partner. In spite of the risk of being discovered in the event of a misstep and the very possible divorce with, in the worst case, the loss of the brood, many bird ladies cannot help but be. The lure of strange male feathers is too great. Why - that is the subject of intensive research to this day. Various theses are circulating. One says: the females want to make sure that all of their eggs are fertilized - even if they have chosen a brood partner with poor sperm quality. According to another, they want to develop further food resources. By copulating with a neighbor, they can invade their territory stress-free and hunt there or collect food or nesting material in some other way. Perhaps they are also testing future partners, says a third research group. The problem: All of these theories are only partially proven.

Bart Kempenaers presented the best indications so far for an indirect benefit. For years, the researcher and his colleagues have examined the paternity relationships and genetic diversity of young birds in a blue tit population. Offspring resulting from affairs actually had a higher genetic diversity than the half-siblings from partner-like sex. The reason is obvious: lovers from more distant territories are less related to the females than the males from their own territory and from immediately neighboring territories. The French biologist Aurélie Choas has even demonstrated a similar mechanism in a mammal, the Alpine marmot. Even more: youngsters conceived by strangers' fathers from infidelities are fitter. "They survive more often," says Kempenaers, "grow better and later have more offspring."


However, the ornithologist from Seewiesen doubts whether such splendid prosperity is solely due to the genetic quality of the lovers - even according to a recently published study by Dutch colleagues. According to this, the eggs inseminated by others are laid earlier, at least in blue tits, which means that the young hatch earlier. This gives them a decisive advantage over their half-brothers and sisters, a kick-start in life - because the parents start feeding immediately. How the females influence the laying sequence depending on paternity is a mystery. Perhaps, from a purely evolutionary point of view, the females are also only victims of male promiscuity, the benefits of which (for the males) are beyond any doubt.

"Drive test" in the basement of the Seewiesen MPI: Wolfgang Forstmeier puts two zebra finches in a cage. Not even five seconds pass - and the male is already singing to the female. “A real Don Juan,” says the ornithologist. The feathered dwarf won't give up until the five minutes of the test are over. Other conspecifics need days before they start courting. Such slow birds later remain sexually loyal to their partner, while the daredevils tend to be on the side. Genes are most likely behind such male promiscuity, even if they are not yet known.

“The males pass these genes on to their daughters,” explains Forstmeier. Exactly that could turn the females into infidelities and diminish their loyalty. In fact, some Vogel ladies are more loyal than others. The biologist has now examined around 1,000 zebra finches for monogamy and polygamy and has delimited regions on the bird chromosomes where fidelity and promiscuity genes could be located. He now wants to find them - and also further clues to the evolutionary processes that make animals polygamous or not.


In the past few years, Forstmeier and his colleagues have systematically investigated how the animals' sexual preferences can be changed in aviaries built especially for the zebra finches. It turned out that not only genes, but also external factors determine sexual behavior. To encourage monogamy, the biologists populated the aviary with equal numbers of males and females, created protected nesting niches, and fed each pair separately. Under such conditions it is said: Advantage for the good fathers! They take care of the offspring intensively, remain loyal to their partners and father most of the boys. However, if the aviary world and the gender distribution change, the machos and daredevils suddenly produce more young - even if the females have to mother the brood alone. “A surplus of females gives the Don Juans advantages; if there are not enough females, aggressive individuals rule the field,” says Forstmeier.


His colleagues from the MPI for Ornithology in Radolfzell and the University of Freiburg observed for the first time how rapidly sexual systems can shift in the wilderness of Australia: in the tails, a genus of songbird species that are notorious for their excessive sexual infidelity. The males can literally be seen cheating: in the breeding season they wrap themselves in a completely colorful plumage, the costume of the playboy, and their reproductive organs are enlarged. And: They give the charmer by charming their potential lover with flower petals.

Sjouke Anne Kingma and his colleagues were completely amazed when they observed that purple-headed easel tails had broken with common customs, even though their way of life is otherwise hardly any different from other types of easel-tails. In Western Australia, the biologists checked 227 offspring from over 100 nests for genetic paternity. The females' social partners almost always fathered the brood. Even more astonishing: the males lack all the characteristics of their promiscuous relatives. There was no longer any charm with flower petals - no flowers for the beloved. The messages from all of this: First, the romantic aspect in the purely monogamous box of two is apparently lost in animals too. Second, there is only a small step between extreme infidelity and almost absolute fidelity. "Mating systems can evidently change faster than expected in the history of development," says Anne Kingma in amazement.

So at least a few species have probably brought about a kind of near monogamy. The females of the crab grebe largely fend off attempts to mate with others. The males of the Dik-Diks, a small African antelope species, guard their partners so strictly that an affair is hardly possible: for "her" because of the big brother effect, for "him" because of a lack of time.


And let's not forget jealousy - or whatever you want to call it with animals. Common marmosets from South America, for example, live in social monogamy - a very strong bond - because the females give birth to twins, whose rearing requires a father's presence. The small primates form families in which only the pair of alpha males and alpha females at the top of the hierarchy reproduce. Biologist Gustl Anzenberger from the University of Zurich examined the animals' loyalty and brought together a male and female from different families. Result: The alpha females resisted any strange male. Alpha males, on the other hand, did it with lower-ranking females - but not in the cage of their own family. The familiar home remained unsullied, "because the alpha female is unmistakably aggressive towards the new couple," emphasizes Anzenberger. The togetherness of these monkeys, interpreted as self-imposed, is more likely based on aggressive-jealous behavior.

The scientist does not see any analogies to humans. Bart Kempenaers, on the other hand, believes that “our research on mating systems is socially relevant”: “Infidelity and jealousy are reality in humans, and it is obvious why this is: our evolutionary history.” New analyzes of the genetic make-up of 90 people from different ethnic groups - Melanesians, Basques, Chinese and three African tribes - provide a clear picture, according to the US geneticist Michael Hammer. Accordingly, "relatively few men have had sex with relatively many women" over the past ten thousand years.


Hammer's team looked at the variety of genetic differences on the female sex chromosome, the X chromosome, and on the rest of the chromosomes. Women have two X chromosomes in their cells, men only one. Apparently the genetic differences on the X chromosome of today's humans are much greater than on “normal” chromosomes. In a population with about the same number of reproductive women and men, however, the reverse would have to be the case, because every child inherits the same number of “normal” chromosomes from father and mother, while a boy only inherits one X chromosome from the mother. For the researchers, the imbalance can only be explained by the fact that many more women than men contributed to the “gene pool” in human evolution. In other words: male polygamy was ubiquitous. Which, on the other hand, means that many men did not get a chance. He was not able to see a trace of sexual monogamy in the genome, says Hammer. Before western culture covered large parts of the planet, 85 percent of all human societies favored some form of polygamy. Even in Western cultures, the harmony of social and sexual monogamy from youth to death, or at least from the (first) partner finding, is the exception.


“Most of the time, we cultivate a serial monogamy,” explains evolutionary biologist David Barash from the University of Wisconsin, who, from a purely evolutionary point of view, also attests that women, from a purely evolutionary point of view, have a tendency to occasionally cheat. One cannot seriously argue about whether monogamy is “natural” for people: “It is not.” You have to say that to people in no uncertain terms. But the predicate “natural” is neither necessarily good, says Barash, nor is “unnatural” behavior beyond human potential. Unlike animals, Homo sapiens do things that seem anything but natural - and often with great devotion. This also applies to a (largely) monogamous or at least serially monogamous life - including sexual fidelity. Barash and his wife, the psychiatrist Judith Lipton, even proclaim a “neural and hormonal infrastructure” that biologically supports monogamy, based on the latest neuroscientific and psychological findings.People therefore need strong bonds - a process that is promoted by feelings of happiness.

The so-called mirror neurons could also promote monogamy by generating empathy for the partner. Good long-term experience with a partner is consolidated in new nerve connections in the brain. Love hormones such as oxytocin or vasopressin combine sexual satisfaction with bondage. Both are dormant in humans: the natural tendency to sexual infidelity - and the power of what we simply call "love". Until the next temptation. ■

KLAUS WILHELM, who has already visited many primate research projects, is amazed at how similar animals and humans are when it comes to topic number 1.

by Klaus Wilhelm



Klaus Wilhelm also produced a radio feature on the subject. The program “Monogamy, Loyalty and Affair” runs on October 18, 2010 at 8:30 am on SWR2 Wissen:


David P. Barash, Judith Eve Lipton STRANGE BEDFELLOWS The Surprising Connection Between Sex, Evolution and Monogamy Bellevue Literary Press, New York 2009, approx. € 22, -


About polyamorie:

"Jealousy is malleable"

Mr. Wirth, how are you doing with your polyamorous relationships?

Quite good! Sometimes it's like an erotic and emotional paradise. But there are also difficult phases.

Does that sound like a lot of “relationship work”?

True, sometimes more so than in a monogamous relationship. But you also get more in return.

What does polyamory mean?

Polyamory means choosing several love relationships that also include eroticism and sex. Long-term commitment and emotional give and take are important here. You really have to be able to get involved. Equality is another important element: women and men are allowed to have multiple relationships. And openness is crucial. There is no such thing as secrecy.

How do you do that in everyday life?

I have a wife, my main wife, so to speak. In addition, I maintain other relationships with female partners whom I meet about once a month. My wife also cultivates her sexual and emotional friendships with other men accordingly.

And does it go smoothly? What if one of the other men wants to monopolize your "main wife"?

The danger is there. To prevent this from happening, the environment is crucial. Before a new partner comes into our lives, we examine the candidate for half a year and then decide together whether we want him or her to join our polyamorous network.

And does it all happen without jealousy?

I am already jealous. But the degree of jealousy is malleable. You can train to stop being so jealous. Today there is only, shall we say, a little uncomfortable tickle left.


· Not only behavioral researchers, but also geneticists are looking for the evolutionary roots of our sexual behavior.

· They found ample evidence of polygamy in the human genome.

· Only love, which is also anchored in our biology, can counteract this: Psychologists have discovered the neuronal and hormonal basis for this.

PICTURE QUIZ FROM PAGE 16/17 - The solution

Sexually (largely) monogamous are: Dik-Dik (picture number 3), mandarin duck (6) and crab grebes (12). Here are the names of the other animals: swan (1), white-handed gibbon (2), zebra finch (4), orca (5), red fox (7), alpine marmot (8), blue tit (9), African elephant ( 10), Leo (11). You all cheat.

October 19, 2010