Competition between human women likely contributed to covert ovulation

Competition for mates between prehistoric human women may have contributed to “ hidden ovulation ” – a lack of noticeable physical cues that a woman is fertile, experts say.

Using computer models, US researchers have found evidence that hidden ovulation in humans – which is unusual in the animal kingdom – has evolved to allow women to hide their fertility status from other females.

This would have helped to avoid female conflicts, possibly motivated by an assault on potential rivals for male partners.

Previously, scientists believed that women had evolved to hide ovulation from men in order to encourage them to care for children.

New research shows that the origin of concealed ovulation may have been focused much more on women than previously thought.

“The study of human evolution has tended to look at things from a male perspective,” said Athena Aktipis, lead author of the study, associate professor of psychology at Arizona State University in the United States. United.

“Even women’s-specific adaptations – like their social behavior and concealed ovulation – were considered in terms of how men shape them.

“Our calculation model shows that female sociality is not just about securing male investments.

Human females are considered to have concealed ovulation because there is no outward physiological sign, either for a woman herself or for others, that ovulation is occurring.

As a result, women rely on useful tools such as charts, test strips, apps or wearable technology to identify periods of fertility.

In contrast, some animals, such as baboons, undergo obvious physical changes during a period of ovulation – most notably, swelling of the perineal skin.

Gradually in the course of human evolution, female fertility is likely to become more and more difficult to detect from an observer’s point of view.

For nearly half a century, the evolution of hidden ovulation in human women has been explained by a theory called the male investment hypothesis.

Essentially, the theory suggests that hidden ovulation was helpful in obtaining male partners to help raise and support children.

This hypothesis has been the predominant explanation for hidden ovulation for decades, although it has undergone some empirical testing and has not been formally modeled until now.

But female primates don’t just interact with males – they interact with each other, sometimes cooperating and sometimes engaged in conflict.

“I’ve been pondering the male investment hypothesis for years, and since you can’t argue with a verbal hypothesis, I started working on how to test it,” Aktipis said.

At the same time, Aktipis was working on “female sociality” – a term to describe female individuals of an animal population who tend to associate in groups.

“ I was struck by the fact that women could have been aggressive against other women showing ovulatory signals which would then create an advantage in concealing ovulation. ”

This theory, dubbed the “female rivalry hypothesis”, is now an alternative and convincing argument for the course of concealed ovulation.

The ovulatory signals are said to have made females more visible as potential rivals for a male partner.

Evolutionary adaptations in humans occur over the timescale of many generations, making it difficult to test whether or how traits may evolve.

Aktipis and his colleagues therefore tested the female rivalry hypothesis using computer modeling, which allows researchers to test ideas that would be difficult to test in the real world.

In agent-based computational models, an “agent” represents an individual whose behavior can be programmed and analyzed.

Each agent follows a specific set of rules and can interact with other agents and with the environment.

In the model developed to test the female rivalry hypothesis, male and female agents followed the rules governing their movement, reproductive behavior, and attractiveness.

Male agents varied in terms of promiscuity – promiscuous men did not partner with women to help raise subsequent children, while non-promiscuous male agents stayed to share resources and support future children.

Female agents had physical signals indicating when ovulation was being concealed.

Female agents could also behave aggressively towards each other.

The female and male agents interacted with each other and had the opportunity to procreate and form parental partnerships.

The model supported the female rivalry hypothesis by showing that women who concealed ovulation fare better, the team found.

They had more children, avoided female-to-female assault, and were successful in forming parental relationships with men.

“Social science work tends to assume that male cognition and behavior is the default,” said Jaimie Arona Krems, lead author of the study, assistant professor of psychology at Oklahoma State University.

“But women regularly face unique challenges, especially in their interactions with other women.

“This work is in part the result of taking this idea seriously.

“When we do this, I think we will learn more, not only about the female spirit, but also about the human spirit.

The research team also used the model to test the male investment hypothesis, running scenarios that did not allow women to behave aggressively towards each other.

But there was no clear benefit to concealing ovulation in this scenario, which again suggests that hidden ovulation evolved due to interactions with other women.

“This work represents a necessary shift in thinking about how human women have evolved,” Aktipis said.

“Female sociality and other adaptations are not just about securing male investment, although this has long been the underlying assumption about female social behavior.

The study was published in Nature Human Behavior.