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According to a new study published by anthropologists at Northwestern University, men have better reproductive success when they spend more time looking after children – not just their children.
In a previous study, researchers found that male wild mountain gorillas living in Rwanda are doing something quite unusual for a mammal: they help take care of all the children in their social group, that 's what they do. they are or are not fathers. . The purpose of the new study was to understand why.
"Mountain gorillas and humans are the only great apes in which men regularly develop close social ties with children. So, find out what mountain gorillas are doing and why we are helping to understand how men may have begun to embark on the path of our more engaged fatherhood. Said Stacy Rosenbaum, lead author of the study and postdoctoral fellow in anthropology at Northwestern.
"Men spend a lot of time with groups of children – and those who flourish and rest more with them have more opportunities for reproduction," said Kuzawa, a professor of art. Anthropology at Northwestern and faculty member of the Institute for Policy Research of the University. . "One likely interpretation is that women choose to marry men based on these interactions."
Rosenbaum added, "We have known for a long time that male mountain gorillas compete for females and mating opportunities, but this new evidence suggests that they may have a more diverse strategy. Even after multiple checks for ranks of dominance, age, and the number of chances of procreation that they have, men who have these ties to children are doing much better.
This research suggests an alternative path through which paternity behaviors may have evolved in our own species, said Rosenbaum.
"Traditionally, we thought that child care depended on a specific social structure, monogamy, because it allowed men to take care of their own children. Our data suggest that there is an alternative path through which evolution can generate this behavior, even when men may not know who their offspring are, "Rosenbaum said.
This raises the possibility that similar behaviors may have been important in the initial establishment of paternity behaviors in distant human ancestors.
Researchers are currently studying whether hormones could help facilitate these male behaviors, as they do in humans. A fundamental work on the hormonal changes that men experience when they become fathers and take care of children was conducted in the Northwestern Anthropology Department.
"In men, testosterone declines as men become fathers, and this would help focus their attention on the needs of the newborn," said Kuzawa, co-author of study on this subject in the journal Proceedings of the National Academy of Sciences in 2011. "Gorillas particularly engaged in interactions with infants could they experience a similar decline in testosterone? Because this would likely hinder their ability to compete with other men, evidence of a decline in testosterone would clearly indicate that they must derive a real benefit, such as attracting partners. Otherwise, if this does not decrease, it suggests that high levels of testosterone and surveillance need not be mutually exclusive in mountain gorillas. "
Researchers are eager to explore these new issues. "We are currently working to characterize the hormonal profiles of these men over time, to determine whether events such as birthing newborns could be related to their testosterone levels," said Rosenbaum. "We are fortunate to have data covering many years of their lives."
The lead author of the study, Tara Stoinski of the Dian Fossey Gorilla Fund, added that such work underscores the critical importance of long-term research.
"Dian Fossey began by studying these mountain gorillas in the 1960s in hopes of better understanding human evolution," Stoinski said. "More than 50 years later, ongoing research on this population continues to provide information not only about an endangered species, but also about what it means to be human."
"Infant care is associated with increased reproductive success in male mountain gorillas" will be published Oct. 15 in Scientific Reports. Besides Rosenbaum, Kuzawa and Stoinski, the paper was co-authored by Linda Vigilant of the Max Planck Institute of Evolutionary Anthropology, Leipzig, Germany.
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