Being happy with the same couple for life is one of the aspirations that sustains civilization, although the relaxation of customs and an ever longer life make it unlikely to fulfill the dream. Although it is a rarity among animals, monogamy, even in an imperfect version, exists in nature, and there are always those who seek in biology a justification for their desires. That is why the studies that investigate the origins of this way of organizing societies, human or animal are so interesting.
This week, the scientific journal PNAS published one of these works. It is about understanding the transition to monogamy of very different types of animals over the last 450 million years. The scientists, led by Rebecca Young, of the University of Texas, in Austin, USA, analyzed five pairs of very similar species in which one was monogamous and the other was not. In the monogamy team, Californian mice were chosen, the prairie voles, a type of bird known as Alpine Pipit, the poisonous frog Ranitomeya imitator and a fish (Xenotilapia) living in Lake Tanganyika in Central Africa. On the polygamous side remained deer mice, the vole pennsylvanicus (the infidels cousins of the prairie voles), the common Accenter, another poisonous Frog (Oophaga pumilio) and another African Cíclido fish.
Variations in a gene can make an individual of a species store the couple stable or not
Despite being very similar species, in one of them males and females were paired at least during the mating season and shared to some extent the tasks of feeding the offspring and defend. These animals were still considered monogamous even if they had some occasional escarceo. Among the polygamous, males tried to spread their sperm as much as possible, but did not care whether their offspring survived or not.
Surprisingly, despite dealing with animals as different as fish or mice, the analysis of the brains of the males revealed that the different expression of the same series of genes was associated with an individual polygamous or one monogamous. The results seem to indicate that monogamy has emerged independently many times throughout history due to the change in expression of genes that are present in both monogamous and promiscuous. In particular, the authors found 24 genes whose activity in the brain has a more intense relationship with monogamous behavior.
Rebecca Young recognizes that they do not know how the function of these genes relates to monogamous inclinations, but dares to speculate. "We know that some of these 24 genes are related to learning or memory, and it is possible that forming a couple's bond or caring for the offspring requires a change in the cognitive processes that are behind social behavior," he explains. "For example, an individual has to be able to recognize his partner and find it gratifying to be with her to create a link," he adds.
One of the species used in this study, the vole of the Prairie, is one of the favorites to try to understand that minority group of mammals that are monogamous. Contrary to what happens to other animals, which shy away from the female after completing her desire, something happens in the brains of the voles that generates a bond that will last forever. These couples take care of their offspring together and do not seem to lose their passion despite marathon mating sessions. Researchers like Larry Young of Emory University discovered that the secret of this way of life was found in the receptors of vasopressin and oxytocin that have the voles in the regions of the brain that regulate the reward. Due to mechanisms similar to those provoked by addictions, the brains of these animals associate a pleasant sensation with the presence of a particular couple. Later, experiments with other species of voles very similar, but promiscuous, showed that if they were given artificially oxytocin and vasopressin also became monogamous.
Even in animals with more monogamous tendencies it is common to produce punctual dabbling
The researcher says that the study is interesting "although it is not known how the system related to monogamy the genes identified." "The study does not tell us how those genes act in the brain to favor monogamy and that is what should be found out in the future," he continues. However, it stresses the importance of knowing that there is a common system in biology whereby many species may end up with monogamous behavior. "It's the first time I've seen anything like this in terms of social behavior," he adds.
For those seeking a clear answer as to whether or not our own species is monogamous by nature, this study does not. "We have not studied this pattern of genetic expression in humans," says Rebecca Young, partly because it is not possible to take the brain of a human to analyze it as they have done with the other animals. But even if it did, it would not find a single pattern.
Even the voles of the prairie, with their intense attachment to their partner, do not renounce a sexual adventure if the occasion arises. In fact, it is estimated that about 10% of the offspring of a couple are not children of the male who cares for them. And not all voles are the same. As Larry Young observed, among the voles, as among humans, there are individuals who are never paired and others who cannot be alone. The investigator was even able to create a system to differentiate the smokers bachelors from those who hook up to his/her orange stocking. The former had a longer version of the gene that produced the vasopressin receptor than the second and were more sensitive to this hormone that helps to create bonds.
Although it is easy to imagine the commercial potential of an application that would permit this type of analysis in humans, even with it, certainty would be elusive. The environment also determines decisions on how to organize life as a couple, both in animals and in humans. "If there are few females or they are difficult to find it can be [practical evolutionary] to stay with her after copulating, because the male does not know when he could find another female," says Rebecca Young. "And so does the pressure of predators or if the environment is very unpredictable. In such cases, both the male and female can benefit from staying together and cooperating in the care of their offspring. "
The researcher believes that one of the teachings that we can apply to our life of studies on monogamy is to know that we humans are also the product of evolution. Understanding how the biological processes that regulate our behavior arose would be like historical knowledge for a ruler. Applying specific recipes from the past today is stupid, but knowing history can help to better interpret the present.