MOSCOW, March 6, Tatyana Pichugina. At the end of the 20th century, American anthropologist Owen Lovejoy suggested that the turning point in human evolution was the transition to monogamy. Strong partnerships literally put a person on two legs and gave him reason. This hypothesis is receiving more and more confirmation.
Voles show miracles of fidelity
Loyalty to one partner is a rather rare phenomenon in the animal world. Among mammals, only five percent of species are monogamous. One notable exception, besides humans, is yellow-bellied voles. They form strong pairs, set up family nests, and care for offspring together.
These small rodents help scientists study the hormonal mechanisms of love, which are based on the reward system. Just two hormones — oxytocin and vasopressin — powerfully control the social behavior of mammals.
Monogamy consists of three stages: courtship, pairing, and maintaining long-term attachment. In a recent study, scientists from the United States identified 68 regions in the brain of yellow-bellied voles that are involved in these processes. Moreover, it is the same in both sexes, contrary to previously widespread belief.
Just half an hour after meeting, the individuals are already copulating, and a day later they have love for life. Both brains respond equally strongly to the male's ejaculation, strengthening the attachment.
“We hypothesize that orgasm in voles promotes the formation of long-term relationships. This is most likely true for humans,” the study’s lead author, Professor Stephen Phelps, told the University of Texas at Austin.
Some statistics
Anthropologists are not inclined to consider people exclusively monogamous. Almost 85 percent of nations approve of polygamy in one form or another; throughout a person’s life, as a rule, a person changes his partner more than once, and in marriage he easily goes to the left. Such data are presented by American scientists in the review “Are We Monogamous?”.
Scientists note the exceptional diversity of love relationships among people: monogamy, polygamy, polyandry, temporary partnerships, numerous forms of marriage and families. But there is one amazing feature — the ability to form long-term love relationships. Moreover, in most cases, a man can be sure that a child born in a family is his. Only two percent of fathers raise children other than their own. For comparison: among birds there are about twenty.
How delicious food made us loyal and dependent
In the 1980s, American anthropologist Owen Lovejoy, famous for his study of the remains of Australopithecus Lucy, suggested that monogamy contributed to the emergence of humans. Later, using new data on Ardipithecus — another transitional form from ancient apes to our ancestors — he developed the theory of hominid evolution.
Before man became upright, developed a large brain, and invented the first tools, Lovejoy argues, he learned to be a caring parent and a faithful partner. This was preceded by a search for a new food strategy in changing environmental conditions. The selection of less aggressive individuals capable of social contacts began, and the need for a stable family arose.
Among our close relatives — chimpanzees and gorillas — males are much more massive than females, with more developed fangs, and much more aggressive. Scientists call this sexual dimorphism. In humans, these differences are not as pronounced. Men are only 15 percent larger, cannot boast of large fangs or testes, and have an easy-going and friendly character. Women, in turn, do not demonstrate readiness to mate. Scientists call this hidden ovulation.
In the new work, Lovejoy and colleagues showedthat a diet rich in fat saturated the nucleus accumbens, a key area of the brain responsible for sociality, with neuropeptide Y and dopamine. As a result, natural selection, which moved towards the development of the reward system in the brain, played a cruel joke on us. We have become smarter, more social, but prone to addiction to delicious fatty foods. This is one of the reasons for the obesity epidemic in the world.
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People are like wolves
Another suitable model for studying monogamy is offered by Christopher Cozans from the University of Mary Washington. These are wolves.
They have similar behavioral traits because they have been forced to survive in the same ecological niche as humans for the last thousands of years. Both species chase prey across open plains using mainly their legs and vision. Living in a group of your own kind allows you to kill animals much larger than yourself. “People are wolves who hunt elephants and whales,” writes the scientist.
Wolves stay in family packs all year round, crossing paths not only for mating. They hunt together and take care of the younger generation. The pack has a social hierarchy, shared ceremonies and meals. These behavioral traits are understandable and useful to people, which apparently helped our ancestors domesticate them, and not, say, chimpanzees or bonobos. Thus, when hunting sables, the peoples of Southern Siberia rely on the mutual understanding of their dogs (once domesticated wolves).
The scientist finds many examples that in both species monogamy arose as a need for long-term raising of offspring. This led to a doubling of neurons responsible for care, socialization, and communication. The family has become a key stage in the evolution of people. When, thanks to collective hunting, they began to produce more meat, they were able to go beyond the borders of Africa and settle throughout the earth in different ecological conditions.