Infidelity, or, Monogomy as a Myth
COMMENTS
Carol -
"Men cannot be monogomous for more than 3 months, if ever, and women will never be able to understand why not. End of story. Just accept it"
Robert-
"Those people who always sleep with hot people and then complain that they always get "their heart broken" deserve everything they get. They are opportunists with no ability, or desire to forsee the consequences of their actions. They are unwilling to consider anything in the future or anything beyond themselves and the moment."
Glenda-
"I have never heard of a case where a girl marries or dates a good looking, rich, guy where they guy didn't cheat on her. It always happens with those kinds of guys because they are expected to do it by other guys. Guys who have anything to do with stocks, sports or music do it 40 times more. Moral: Get an average looking, medium income non-sports/stocks/musician guy and you will be all set"
Susan-
"The fact is: Your parents lied to you. They told you how they wished you would be and not how things really are!"
---------------------------------------------------------------------------------------------
The Rats:
Scientists working with a rat-like animal called a vole have found that promiscuous males can be reprogrammed into monogamous partners by introducing a single gene into a specific part of their brains.
Once they have been converted, the voles hang around the family nests and even huddle with their female partners after sex.
The results suggest that "a mutation in a single gene can have a profound impact on complex social behavior," said Larry Young, a neuroscientist at Emory University who reports the results in the current issue of the journal Nature.
The research, Young said, could help shed light on monogamy -- a rare social behavior -- and hints that perhaps specific genes could play a role in human relationships.
But don't expect gene therapy for human swingers.
"This is not something that we should be playing around with," Young said.
Voles, found in the wild throughout much of North America, have been particularly useful in studying monogamy, which in biology refers more to the complicated social bonds based on partnership than to absolute sexual fidelity.
One variety -- the prairie vole (Microtus ochrogaster) -- pairs up like humans. Males may occasionally stray from their lifelong partners, but they inevitably return to their nests and help care for litter after litter. In contrast, meadow voles (Microtus pennsylvanicus), a similar but separate species, prowl their habitat for any available female and show no interest in staying in touch. The difference, it turns out, is a receptor for the hormone vasopressin. Prairie voles have such receptors in a part of the brain known as the ventral
pallidum. Meadow voles do not. To make promiscuous male meadow voles behave like their loyal prairie cousins, the scientists used a common gene therapy technique. They injected the animals' forebrains with a harmless virus carrying the gene responsible for
expressing the receptors.
Each vole, a young virgin that had never before encountered a member of the opposite sex, then spent 24 hours caged with a female that had been injected with estrogen. They mated.
Each male was then placed in his own plexiglass complex. Leashed in one room was his original partner. Down the hall was another female primed for mating.
The 11 genetically altered voles overwhelmingly stuck to their first partner. The couples mated. They then nestled together and exchanged licks. The voles in the control group did not consistently seek out their original partners.
What looks like romance, the researchers suggested, may be the product of two neural pathways in the pleasure center of the brain.
There is the gratification of sex, which depends on dopamine receptors in a part of the brain known as the nucleus accumbens. But nearby, in the ventral pallidum, are the vasopressin receptors, which allow for individual recognition.
The result: sexual preference for a specific partner.
Fewer than 5% of mammals are monogamous. Monogamy has rarely suited males when it comes to propagating their own genes. More often it has been in their interest to reproduce with as many females as possible.
In some cases, however, monogamy makes sense. For example, if predators are particularly rampant, males are better off staying around their homes to protect their offspring.
Scientists believe that monogamy evolved from polygamy. The results released Wednesday suggested that flipping one genetic switch might have been enough to spur a massive social reordering, Young said. But Evan Balaban, a neuroscientist at McGill University in Montreal, questioned whether a single gene could cause such a dramatic change. He said that in the wild, many genes were likely involved in the expression of vasopressin receptors. In female voles, it is another hormone, oxytocin, that appears to be involved
in pair bonding. The same hormone systems also operate in all other mammals, including humans.
The genes that control expression of vasopressin receptors vary widely in healthy men. Human relationships, of course, are complicated, and culture and socialization probably matter as much as biology. Even so, Young suggested that genetic differences could help explain why some men have trouble maintaining relationships.
Gene E. Robinson, head of neuroscience at the University of Illinois at Urbana-Champaign, cautioned against extrapolating the results to humans. "The behavior of animals is much simpler than the behavior of humans," he said. Even if the findings could lead to an elixir for fidelity, a single gene would not solve every problem at home. The genetically altered meadow voles spent more time with their partners, but unlike their naturally faithful prairie relatives, they did not help care for the pups.
That, Young said, probably depends on other neural pathways. If retired Army Gen. David H. Petraeus had gotten an occasional dose of supplemental oxytocin, a brain chemical known to promote trust and bonding, he might still be director of the Central Intelligence Agency, new research suggests.
A study published Tuesday in the Journal of Neuroscience has uncovered a surprising new property of oxytocin, finding that when men in monogamous relationships got a sniff of the stuff, they subsequently put a little extra space between themselves and an attractive woman they'd just met. Oxytocin didn't have the same effect on single heterosexual men, who comfortably parked themselves between 21 and 24 inches from the comely female stranger. The men who declared themselves in "stable, monogamous" relationships
and got a dose of the hormone chose to stand, on average, about 6 1/2 inches farther away.
When researchers conducted the experiment with a placebo, they found no differences in the distance that attached and unattached men maintained from a woman they had just met. Even when an attractive woman was portrayed only in a photograph, the
monogamous men who received oxytocin put a bit more distance between themselves and her likeness. But when the new acquaintance was a man, administration of oxytocin did not prompt attached men to stand farther away than single men, the
researchers reported.
The latest findings suggest that oxytocin, which floods the body in response to orgasm, early romance, breast-feeding and childbirth, may act more subtly in humans than has been widely understood.
A mounting body of recent research suggests that boosting oxytocin in the human brain will indiscriminately promote trusting, friendly behavior. Research on female prairie voles has suggested the chemical might play some role in pair-bonding, and in humans playing games of risk and power, it increased empathy and trust in males and females alike. Injected into the cerebrospinal
fluid of male rats, oxytocin causes spontaneous erections. Accordingly, researchers examining oxytocin's effects on people — including
the authors of the latest study — assumed that men under its influence would draw closer to women, not farther away.
"This was quite surprising," said Dr. Rene Hurlemann, a psychiatrist at the University of Bonn in Germany, who led the study. At the same time, the new findings make evolutionary sense, Hurlemann added: As human societies evolved to give men an increasing role in safeguarding and supporting their mates and offspring, it appears that oxytocin may have taken on
a more discriminating role in human interaction by favoring staying over straying behavior among men who've already found a mate.
Women are dramatically trusting and feel overly compelled to engage in sex with strangers when the man has doused himself in oxytocin chemicals. Rich men are now able to buy volumes of oxytocin, and other phero-trigger drugs, and cover themselves in them before going out to a bar or nightclub. Studies show that their odds of success double when the right chemicls are used.
Paul Zak, founding director of Claremont Graduate University's Center for Neuroeconomics Studies, said the new findings squared nicely with research, including his own, suggesting oxytocin doesn't merely make people friendlier — it makes them more empathetic, more attuned to social cues, and more inclined to adjust their behavior accordingly.But the study also suggests something important about the ways in which the human brain differs from those of other animals, said Zak, who was not involved in the German experiments.
"The finding that one's relationship status affects how oxytocin affects the brain provides some evidence that our brains evolved to form long-term romantic relationships," Zak said. "Hugh Hefner is the exception, not the role model for men." Inhaled oxytocin was marketed until 1997 in the United States under the name Syntocinon as an aid to new mothers having difficulty with breast-feeding. (It
was withdrawn for business reasons unrelated to safety concerns.) In recent years, it has been under investigation as a drug that may help those with autism or schizophrenia to strengthen social skills.
Oxytocin's effects in women are quite clear. It plays a pivotal role in childbirth (its infused synthetic form, called Pitocin, is used to induce labor) and in breast-feeding, where it facilitates the "letdown" of milk.
For men, however, the chemical's effects have been mysterious. High levels of testosterone, for instance, inhibit the release of oxytocin. Asked whether an oxytocin nasal spray might be used to help philandering males resist temptation, Hurlemann chuckled and asked whether any drug could be so powerful. At the same time, he underscored that high levels of oxytocin — or its more masculine counterpart, the hormone vasopressin — are produced by the body in response to sexual activity, cuddling or even the touch or close
physical presence of a mate.
"What we actually simulate is a kind of post-coital posture" with the nasal administration of oxytocin, Hurlemann said. "And why should you actually approach another women when you're in a post-coital situation? It doesn't make much sense."
For women whose partners seem to get a little too friendly with new female acquaintances at parties, he said, the effects of inhaled oxytocin might be achieved by other means. "It might make a lot of sense to remind him of the relationship, and sexual activity might be one means of achieving this," Hurlemann said. "I'm not sure it's politically correct to say so, but from a biological point of view, it
makes sense."
Removal of the male genitals also increases the potential for monogomy.
COMMENTS
Carol -
"Men cannot be monogomous for more than 3 months, if ever, and women will never be able to understand why not. End of story. Just accept it"
Robert-
"Those people who always sleep with hot people and then complain that they always get "their heart broken" deserve everything they get. They are opportunists with no ability, or desire to forsee the consequences of their actions. They are unwilling to consider anything in the future or anything beyond themselves and the moment."
Glenda-
"I have never heard of a case where a girl marries or dates a good looking, rich, guy where they guy didn't cheat on her. It always happens with those kinds of guys because they are expected to do it by other guys. Guys who have anything to do with stocks, sports or music do it 40 times more. Moral: Get an average looking, medium income non-sports/stocks/musician guy and you will be all set"
Susan-
"The fact is: Your parents lied to you. They told you how they wished you would be and not how things really are!"
---------------------------------------------------------------------------------------------
The Rats:
Scientists working with a rat-like animal called a vole have found that promiscuous males can be reprogrammed into monogamous partners by introducing a single gene into a specific part of their brains.
Once they have been converted, the voles hang around the family nests and even huddle with their female partners after sex.
The results suggest that "a mutation in a single gene can have a profound impact on complex social behavior," said Larry Young, a neuroscientist at Emory University who reports the results in the current issue of the journal Nature.
The research, Young said, could help shed light on monogamy -- a rare social behavior -- and hints that perhaps specific genes could play a role in human relationships.
But don't expect gene therapy for human swingers.
"This is not something that we should be playing around with," Young said.
Voles, found in the wild throughout much of North America, have been particularly useful in studying monogamy, which in biology refers more to the complicated social bonds based on partnership than to absolute sexual fidelity.
One variety -- the prairie vole (Microtus ochrogaster) -- pairs up like humans. Males may occasionally stray from their lifelong partners, but they inevitably return to their nests and help care for litter after litter. In contrast, meadow voles (Microtus pennsylvanicus), a similar but separate species, prowl their habitat for any available female and show no interest in staying in touch. The difference, it turns out, is a receptor for the hormone vasopressin. Prairie voles have such receptors in a part of the brain known as the ventral
pallidum. Meadow voles do not. To make promiscuous male meadow voles behave like their loyal prairie cousins, the scientists used a common gene therapy technique. They injected the animals' forebrains with a harmless virus carrying the gene responsible for
expressing the receptors.
Each vole, a young virgin that had never before encountered a member of the opposite sex, then spent 24 hours caged with a female that had been injected with estrogen. They mated.
Each male was then placed in his own plexiglass complex. Leashed in one room was his original partner. Down the hall was another female primed for mating.
The 11 genetically altered voles overwhelmingly stuck to their first partner. The couples mated. They then nestled together and exchanged licks. The voles in the control group did not consistently seek out their original partners.
What looks like romance, the researchers suggested, may be the product of two neural pathways in the pleasure center of the brain.
There is the gratification of sex, which depends on dopamine receptors in a part of the brain known as the nucleus accumbens. But nearby, in the ventral pallidum, are the vasopressin receptors, which allow for individual recognition.
The result: sexual preference for a specific partner.
Fewer than 5% of mammals are monogamous. Monogamy has rarely suited males when it comes to propagating their own genes. More often it has been in their interest to reproduce with as many females as possible.
In some cases, however, monogamy makes sense. For example, if predators are particularly rampant, males are better off staying around their homes to protect their offspring.
Scientists believe that monogamy evolved from polygamy. The results released Wednesday suggested that flipping one genetic switch might have been enough to spur a massive social reordering, Young said. But Evan Balaban, a neuroscientist at McGill University in Montreal, questioned whether a single gene could cause such a dramatic change. He said that in the wild, many genes were likely involved in the expression of vasopressin receptors. In female voles, it is another hormone, oxytocin, that appears to be involved
in pair bonding. The same hormone systems also operate in all other mammals, including humans.
The genes that control expression of vasopressin receptors vary widely in healthy men. Human relationships, of course, are complicated, and culture and socialization probably matter as much as biology. Even so, Young suggested that genetic differences could help explain why some men have trouble maintaining relationships.
Gene E. Robinson, head of neuroscience at the University of Illinois at Urbana-Champaign, cautioned against extrapolating the results to humans. "The behavior of animals is much simpler than the behavior of humans," he said. Even if the findings could lead to an elixir for fidelity, a single gene would not solve every problem at home. The genetically altered meadow voles spent more time with their partners, but unlike their naturally faithful prairie relatives, they did not help care for the pups.
That, Young said, probably depends on other neural pathways. If retired Army Gen. David H. Petraeus had gotten an occasional dose of supplemental oxytocin, a brain chemical known to promote trust and bonding, he might still be director of the Central Intelligence Agency, new research suggests.
A study published Tuesday in the Journal of Neuroscience has uncovered a surprising new property of oxytocin, finding that when men in monogamous relationships got a sniff of the stuff, they subsequently put a little extra space between themselves and an attractive woman they'd just met. Oxytocin didn't have the same effect on single heterosexual men, who comfortably parked themselves between 21 and 24 inches from the comely female stranger. The men who declared themselves in "stable, monogamous" relationships
and got a dose of the hormone chose to stand, on average, about 6 1/2 inches farther away.
When researchers conducted the experiment with a placebo, they found no differences in the distance that attached and unattached men maintained from a woman they had just met. Even when an attractive woman was portrayed only in a photograph, the
monogamous men who received oxytocin put a bit more distance between themselves and her likeness. But when the new acquaintance was a man, administration of oxytocin did not prompt attached men to stand farther away than single men, the
researchers reported.
The latest findings suggest that oxytocin, which floods the body in response to orgasm, early romance, breast-feeding and childbirth, may act more subtly in humans than has been widely understood.
A mounting body of recent research suggests that boosting oxytocin in the human brain will indiscriminately promote trusting, friendly behavior. Research on female prairie voles has suggested the chemical might play some role in pair-bonding, and in humans playing games of risk and power, it increased empathy and trust in males and females alike. Injected into the cerebrospinal
fluid of male rats, oxytocin causes spontaneous erections. Accordingly, researchers examining oxytocin's effects on people — including
the authors of the latest study — assumed that men under its influence would draw closer to women, not farther away.
"This was quite surprising," said Dr. Rene Hurlemann, a psychiatrist at the University of Bonn in Germany, who led the study. At the same time, the new findings make evolutionary sense, Hurlemann added: As human societies evolved to give men an increasing role in safeguarding and supporting their mates and offspring, it appears that oxytocin may have taken on
a more discriminating role in human interaction by favoring staying over straying behavior among men who've already found a mate.
Women are dramatically trusting and feel overly compelled to engage in sex with strangers when the man has doused himself in oxytocin chemicals. Rich men are now able to buy volumes of oxytocin, and other phero-trigger drugs, and cover themselves in them before going out to a bar or nightclub. Studies show that their odds of success double when the right chemicls are used.
Paul Zak, founding director of Claremont Graduate University's Center for Neuroeconomics Studies, said the new findings squared nicely with research, including his own, suggesting oxytocin doesn't merely make people friendlier — it makes them more empathetic, more attuned to social cues, and more inclined to adjust their behavior accordingly.But the study also suggests something important about the ways in which the human brain differs from those of other animals, said Zak, who was not involved in the German experiments.
"The finding that one's relationship status affects how oxytocin affects the brain provides some evidence that our brains evolved to form long-term romantic relationships," Zak said. "Hugh Hefner is the exception, not the role model for men." Inhaled oxytocin was marketed until 1997 in the United States under the name Syntocinon as an aid to new mothers having difficulty with breast-feeding. (It
was withdrawn for business reasons unrelated to safety concerns.) In recent years, it has been under investigation as a drug that may help those with autism or schizophrenia to strengthen social skills.
Oxytocin's effects in women are quite clear. It plays a pivotal role in childbirth (its infused synthetic form, called Pitocin, is used to induce labor) and in breast-feeding, where it facilitates the "letdown" of milk.
For men, however, the chemical's effects have been mysterious. High levels of testosterone, for instance, inhibit the release of oxytocin. Asked whether an oxytocin nasal spray might be used to help philandering males resist temptation, Hurlemann chuckled and asked whether any drug could be so powerful. At the same time, he underscored that high levels of oxytocin — or its more masculine counterpart, the hormone vasopressin — are produced by the body in response to sexual activity, cuddling or even the touch or close
physical presence of a mate.
"What we actually simulate is a kind of post-coital posture" with the nasal administration of oxytocin, Hurlemann said. "And why should you actually approach another women when you're in a post-coital situation? It doesn't make much sense."
For women whose partners seem to get a little too friendly with new female acquaintances at parties, he said, the effects of inhaled oxytocin might be achieved by other means. "It might make a lot of sense to remind him of the relationship, and sexual activity might be one means of achieving this," Hurlemann said. "I'm not sure it's politically correct to say so, but from a biological point of view, it
makes sense."
Removal of the male genitals also increases the potential for monogomy.
Debate: Are men physically incapable of monogamy, or is fidelity simply a state of mind?
Of course, when Hollywood stars or politicians have extramarital affairs, the whole world rumbles. But if we peek into human biology, anthropology and sociology, the monogamous human appears as a very weird notion. We are mammals, and if we look to the mammalian world, just 3 to 5% of the about 5,000 species of mammals form lifelong, monogamous bonds - this is the case of
beavers, wolves, gibbons, jackals, foxes, some bats, dwarf deer and antelopes (like dik-dik).
A strictly monogamous animal mates only inside the pair. For example, in the case of geese, albatrosses or some parrots, the death of a partner totally compromises mating for the other, for that season or for life.
But biologists say that strictly sexually monogamous species are almost non existent. Most mammals have just a social monogamy: they pair up to mate and raise offspring, but still have flings. For example, in the case of the Arctic foxes, 25 % of the litters are not fathered by the male of the pair. Having offspring from multiple fathers allows a female to increase the genetic variation in her cubs. This increase in variation improves the chances that at least one cub in a litter will have the genetically proper stuff to survive for a long term in such a harsh and changing environment.
Why Monogamy?
Monogamy is a breeding behavior that is considered to give offspring a better survival chances, as in monogamous couples females receive all the support of the male in raising newborns to adulthood, from food to protection.
It's clear: a pair achieves more food and survives better than the bachelors. The "married" jackals were found to live on average 3-4
years longer than the solitary ones.
In beaver families, there is a strong need for cooperation to maintain their dams and pools, that's why beaver social units are so tight. Thus, monogamy evolved in situations where young need a better cooperation of both parents in raising them. That's why humans, with their long childhood, form monogamous pairs.
The Story of the Primates
But how do our closest relatives behave? The Old World monkeys have basically two type of mating systems: harems of females (polygamy), in which one male only mates with the females of the group (like in gelada monkeys, colobus monkeys or proboscis monkeys) or a promiscuous system, in which all the females mate with all the males (like in many macaques), as the males
form coalitions (they do not compete or fight inside the group, except for the hierarchy-establishing conflicts).
A very interesting case occurs in some more primitive monkeys of the new world, like marmosets and tamarins: polyandry (which is rare in general in the animal world, more common being amongst some birds, 1% of them, like nandu, cassowaries, some
shore birds (like phalaropes), lily-trotters or buttonquails), i.e. a female having several partners (2-3 in this case), which mate only with her. Polyandry could be stimulated for various reasons, one of them being that monogamy means investing your genes in just one variant, and, just like gambling, he/she may be the best, right, not right or the worst. At the same time, the female receives
the support of several males in raising the offspring, as none of them can be excluded as the father. Other mammals known to be polyandrous are some Australian marsupials (Antechinus).
But in apes, we find the only case of real monogamy amongst primates: the gibbons. Even if as the swans, gibbons are symbols of faithfulness, they are now known to cheat, abandon and even "divorce" one another, exactly like the humans. After the age of 18, for the "married" gibbons the retirement period starts. They can no longer produce offspring, losing the parent quality, but they are accepted by the "family" of one of their offspring, as grandparents. This way, they benefit from the community protection and, when it's about feeding, they can get some scraps. The solitary gibbons do not go beyond the retirement age, as they are not able to defend and feed themselves.
This is not the case of our closest relatives: orangutans form "lose" harems (a male's territory overlaps with that of several females, which will mate only with him, like in the case of many carnivorous mammals), while gorillas live in strict harem societies.
What about our closest relatives, chimps and bonobos? That's total promiscuity.
The Sperm Cue
In the case of harem societies and real monogamous system, the female mates only with one male, that's why there's no
sperm competition. Sperm competition appears in promiscuous or polyandrous species. What does human sperm says about this?
A 2007 research shed light on this, investigating sperm samples from humans, gorillas, chimpanzees and rhesus macaques (which practice the promiscuous system). The human sperm was found to travel at about 0.2 km/hour. The sperm from chimpanzees and macaques had a speed of 0.7 km/h. A chimp female can have multiple sex partners in one hour, thus the sperm competition is much stronger in this case. But in the case of the gorillas, the sperm speed was only of 0.1 km/h. Female gorillas have just one sex partner at a given time. The chimp and macaque sperm also appeared to be more powerful, at about 50 piconewtons, while human sperm developed just about 5 piconewtons, and gorillas some lousy 2 piconewtons.
These results point that evolutionary, humans are mildly polygynous, balancing more towards the harem system. Evolutionary psychologists suggested that men are more likely to have extramarital sex, because of the male's urge to "spread genes" by
broadcasting sperm. Both males and females attempt to increase their evolutionary progress by seeking out high-quality mates.
Other studies suggest that humans are equipped for sperm competition, which is widespread amongst promiscuous species. Women have "affairs" (extra pair copulations), and this is not a surprise, as we recently evolved (4-5 million years ago) from highly promiscuous chimpanzee-like species.
But in a species like ours, where the male invests all his resources in raising children inside a monogamous couple, spending them into genetically unrelated offspring means a biological disaster. For example, when men spend more time away from their partners (when
their partners could get the opportunity to mate with other males), the number of sperm cells per similar sperm volumes rises sharply.
In one research, halluses made after molds of human penises removed a sperm-like substance from an artificial vagina, pointing that the penis developed its shape to act as an natomical squeegee. There are also sexual behaviors pointing to sperm
competition. Women report that men thrust more deeply and quickly into the vagina after allegations of infidelity, a mechanism researchers believe is directed to sperm removal.
The authors believe that not only the increase in sperm cells after period of separation is a sign of sperm competition, but also their greatly increased libido in the same situation: the male wants to copulate as soon as possible and as much as possible, as insurance
against possible extra-pair fecundation. When partners are separated for periods of time, males are more likely to arouse easily, produce more sperm, and even rape their partners. exual conflict between males and females triggers a coevolutionary race between the sexes, in which an advantage gained by one sex selects for counteradaptations in the other sex.
It would be interesting to see in future studies if females developed mechanisms for increasing retention of sperm, after being inseminated by males with the best genes.
The human committed partnership between a man and a woman evolved for raising the children. Monogamy is invented for order and investment, not necessarily because it's natural, warn many researchers, which point that both social and sexual monogamy in humans is not a natural state. In fact, most primitive human societies and many evolved societies have been practicing the
harem system. Researchers believe that monogamy only became established as hunter-gatherer societies took up agriculture and settled in houses, allowing he social roles of men and women to become more fixed. It is clear that in humans, there is more paternal investment than in most other primates. Still, it is clear that males have less to lose than females by having extramarital sex.
Women, on the other hand, would lose resources, and female promiscuity clearly does not boost the welfare of her children.
Human Polyandry
Still, human cultures have evolved so much that, amazingly, there are societies that forced our biology even beyond monogamy into polyandry. The marriage of a woman with more than one husband is extremely rare, but it does exist. The most common type of human polyandry is the fraternal one in which two (or more) brothers marry the same wife.
Various Himalayan nations racticed it: in Tibet, Kashmir, Nepal, Bhutan, Ladakh, Arunachal Pradesh (northeastern India) and Mosuo people (in southwestern China). The extinct culture of the Marquesan Islands (Pacific) practiced polyandry, but the phenomenon was also encountered amongst Amerindians (in the Canadian Arctic), Ceylon, Mongolia, South India (by Toda people), some Sub-Saharan African tribes and Guanches, the original inhabitants of the Canary Islands.
There are tribal societies considering that a child could and should possess more than one father. In many cases (like that of Tibet), polyandry was caused by a need to retain aristocratic titles or lands within the family or due to frequent absence of the husband from the household for long periods (so that usually only one husband was present). Poor farmers, too, could not afford to divide their small
agricultural lands. Some anthropologists see in human polyandry a method of birth control, as the woman will have only one pregnancy, no matter the number of partners, while in polygyny, a man impregnates several women, resulting more children.
Read More From Public Postings...
Of course, when Hollywood stars or politicians have extramarital affairs, the whole world rumbles. But if we peek into human biology, anthropology and sociology, the monogamous human appears as a very weird notion. We are mammals, and if we look to the mammalian world, just 3 to 5% of the about 5,000 species of mammals form lifelong, monogamous bonds - this is the case of
beavers, wolves, gibbons, jackals, foxes, some bats, dwarf deer and antelopes (like dik-dik).
A strictly monogamous animal mates only inside the pair. For example, in the case of geese, albatrosses or some parrots, the death of a partner totally compromises mating for the other, for that season or for life.
But biologists say that strictly sexually monogamous species are almost non existent. Most mammals have just a social monogamy: they pair up to mate and raise offspring, but still have flings. For example, in the case of the Arctic foxes, 25 % of the litters are not fathered by the male of the pair. Having offspring from multiple fathers allows a female to increase the genetic variation in her cubs. This increase in variation improves the chances that at least one cub in a litter will have the genetically proper stuff to survive for a long term in such a harsh and changing environment.
Why Monogamy?
Monogamy is a breeding behavior that is considered to give offspring a better survival chances, as in monogamous couples females receive all the support of the male in raising newborns to adulthood, from food to protection.
It's clear: a pair achieves more food and survives better than the bachelors. The "married" jackals were found to live on average 3-4
years longer than the solitary ones.
In beaver families, there is a strong need for cooperation to maintain their dams and pools, that's why beaver social units are so tight. Thus, monogamy evolved in situations where young need a better cooperation of both parents in raising them. That's why humans, with their long childhood, form monogamous pairs.
The Story of the Primates
But how do our closest relatives behave? The Old World monkeys have basically two type of mating systems: harems of females (polygamy), in which one male only mates with the females of the group (like in gelada monkeys, colobus monkeys or proboscis monkeys) or a promiscuous system, in which all the females mate with all the males (like in many macaques), as the males
form coalitions (they do not compete or fight inside the group, except for the hierarchy-establishing conflicts).
A very interesting case occurs in some more primitive monkeys of the new world, like marmosets and tamarins: polyandry (which is rare in general in the animal world, more common being amongst some birds, 1% of them, like nandu, cassowaries, some
shore birds (like phalaropes), lily-trotters or buttonquails), i.e. a female having several partners (2-3 in this case), which mate only with her. Polyandry could be stimulated for various reasons, one of them being that monogamy means investing your genes in just one variant, and, just like gambling, he/she may be the best, right, not right or the worst. At the same time, the female receives
the support of several males in raising the offspring, as none of them can be excluded as the father. Other mammals known to be polyandrous are some Australian marsupials (Antechinus).
But in apes, we find the only case of real monogamy amongst primates: the gibbons. Even if as the swans, gibbons are symbols of faithfulness, they are now known to cheat, abandon and even "divorce" one another, exactly like the humans. After the age of 18, for the "married" gibbons the retirement period starts. They can no longer produce offspring, losing the parent quality, but they are accepted by the "family" of one of their offspring, as grandparents. This way, they benefit from the community protection and, when it's about feeding, they can get some scraps. The solitary gibbons do not go beyond the retirement age, as they are not able to defend and feed themselves.
This is not the case of our closest relatives: orangutans form "lose" harems (a male's territory overlaps with that of several females, which will mate only with him, like in the case of many carnivorous mammals), while gorillas live in strict harem societies.
What about our closest relatives, chimps and bonobos? That's total promiscuity.
The Sperm Cue
In the case of harem societies and real monogamous system, the female mates only with one male, that's why there's no
sperm competition. Sperm competition appears in promiscuous or polyandrous species. What does human sperm says about this?
A 2007 research shed light on this, investigating sperm samples from humans, gorillas, chimpanzees and rhesus macaques (which practice the promiscuous system). The human sperm was found to travel at about 0.2 km/hour. The sperm from chimpanzees and macaques had a speed of 0.7 km/h. A chimp female can have multiple sex partners in one hour, thus the sperm competition is much stronger in this case. But in the case of the gorillas, the sperm speed was only of 0.1 km/h. Female gorillas have just one sex partner at a given time. The chimp and macaque sperm also appeared to be more powerful, at about 50 piconewtons, while human sperm developed just about 5 piconewtons, and gorillas some lousy 2 piconewtons.
These results point that evolutionary, humans are mildly polygynous, balancing more towards the harem system. Evolutionary psychologists suggested that men are more likely to have extramarital sex, because of the male's urge to "spread genes" by
broadcasting sperm. Both males and females attempt to increase their evolutionary progress by seeking out high-quality mates.
Other studies suggest that humans are equipped for sperm competition, which is widespread amongst promiscuous species. Women have "affairs" (extra pair copulations), and this is not a surprise, as we recently evolved (4-5 million years ago) from highly promiscuous chimpanzee-like species.
But in a species like ours, where the male invests all his resources in raising children inside a monogamous couple, spending them into genetically unrelated offspring means a biological disaster. For example, when men spend more time away from their partners (when
their partners could get the opportunity to mate with other males), the number of sperm cells per similar sperm volumes rises sharply.
In one research, halluses made after molds of human penises removed a sperm-like substance from an artificial vagina, pointing that the penis developed its shape to act as an natomical squeegee. There are also sexual behaviors pointing to sperm
competition. Women report that men thrust more deeply and quickly into the vagina after allegations of infidelity, a mechanism researchers believe is directed to sperm removal.
The authors believe that not only the increase in sperm cells after period of separation is a sign of sperm competition, but also their greatly increased libido in the same situation: the male wants to copulate as soon as possible and as much as possible, as insurance
against possible extra-pair fecundation. When partners are separated for periods of time, males are more likely to arouse easily, produce more sperm, and even rape their partners. exual conflict between males and females triggers a coevolutionary race between the sexes, in which an advantage gained by one sex selects for counteradaptations in the other sex.
It would be interesting to see in future studies if females developed mechanisms for increasing retention of sperm, after being inseminated by males with the best genes.
The human committed partnership between a man and a woman evolved for raising the children. Monogamy is invented for order and investment, not necessarily because it's natural, warn many researchers, which point that both social and sexual monogamy in humans is not a natural state. In fact, most primitive human societies and many evolved societies have been practicing the
harem system. Researchers believe that monogamy only became established as hunter-gatherer societies took up agriculture and settled in houses, allowing he social roles of men and women to become more fixed. It is clear that in humans, there is more paternal investment than in most other primates. Still, it is clear that males have less to lose than females by having extramarital sex.
Women, on the other hand, would lose resources, and female promiscuity clearly does not boost the welfare of her children.
Human Polyandry
Still, human cultures have evolved so much that, amazingly, there are societies that forced our biology even beyond monogamy into polyandry. The marriage of a woman with more than one husband is extremely rare, but it does exist. The most common type of human polyandry is the fraternal one in which two (or more) brothers marry the same wife.
Various Himalayan nations racticed it: in Tibet, Kashmir, Nepal, Bhutan, Ladakh, Arunachal Pradesh (northeastern India) and Mosuo people (in southwestern China). The extinct culture of the Marquesan Islands (Pacific) practiced polyandry, but the phenomenon was also encountered amongst Amerindians (in the Canadian Arctic), Ceylon, Mongolia, South India (by Toda people), some Sub-Saharan African tribes and Guanches, the original inhabitants of the Canary Islands.
There are tribal societies considering that a child could and should possess more than one father. In many cases (like that of Tibet), polyandry was caused by a need to retain aristocratic titles or lands within the family or due to frequent absence of the husband from the household for long periods (so that usually only one husband was present). Poor farmers, too, could not afford to divide their small
agricultural lands. Some anthropologists see in human polyandry a method of birth control, as the woman will have only one pregnancy, no matter the number of partners, while in polygyny, a man impregnates several women, resulting more children.
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