Competition between human women likely contributed to covert ovulation

Human women rely on aids such as charts, test strips or wearable technology to identify periods of fertility. Some animals, like baboons, undergo obvious physical changes during ovulation. How has fertility become so difficult to detect in humans?

For nearly half a century, the evolution of hidden ovulation in human women has been shown to be helpful in ensuring that male partners help raise and support children. A study published on January 25 in Human behavior of nature questions this long-held idea. Using agent-based computational models, a team of evolutionary scientists showed that hidden ovulation could in fact have evolved to allow women to hide their fertility status from other women.

“The study of human evolution has tended to look at things from a male perspective, and even female-specific adaptations – like their social behavior and concealed ovulation – have been viewed in terms of how which men shape them. This study challenges the idea that the role of female sociality is to better secure male partners and their resources; our computer model shows that female sociality is much more than securing the male investment, ”said Athena Aktipis, associate professor of psychology at Arizona State University and lead author of the article.

Get out with the old, get in with the new

The idea that women have evolved to conceal ovulation from men to encourage them to help with children, known as the male investment hypothesis, has been proposed as a way to understand why human women do not advertise. ovulation. This hypothesis has been the predominant explanation for female sociality and hidden ovulation for decades, although it has undergone little empirical testing and has not been formally modeled until now.

But women don’t just interact with men. They interact with each other, sometimes cooperate, and sometimes engage 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, I was working on female sociality and was struck by the fact that women could have been aggressive against other females showing ovulatory signals, which would then create an advantage in concealing ovulation.”

The team of evolutionary scientists tested the idea that female conflict may have resulted in the evolution of concealed ovulation, which they call the female rivalry hypothesis, using an agent-based computational model. Evolutionary adaptations in humans occur over the timescale of many generations, making it difficult to test whether or how traits may evolve. Computer modeling 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 team up 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 assault 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. They had more children, avoided female-to-female assault, and were successful in forming parental relationships with men.

“Social science work has tended to assume that male cognition and behavior is the default. 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. we do this, I think we will learn more, not only about the female spirit, but also about the human spirit, ”said Jaimie Arona Krems, assistant professor of psychology at Oklahoma State University and first author of the ‘article.

The research team also used the model to test the male investment hypothesis, running scenarios that did not allow women to attack each other. But there was no clear benefit to concealing ovulation in this scenario, suggesting that hidden ovulation in women might not have evolved due to interactions with men, but rather due to interactions with other women.

“This work represents a necessary shift in thinking about how human women have evolved. Female sociality and other adaptations are not just about securing male investment, although this has long been the under- assumption. underlying the purpose of women’s social behavior, ”Aktipis said.