Study highlights the decisive role of women

Female and male primates often form close bonds, but not just out of affection. Close relationships usually develop when there is a clear benefit to both parties, with protection and control of reproduction playing a key role.

A new study, led by primatologists Liesbeth Sterck of Utrecht University and Julia Ostner of the University of Göttingen, provides theoretical insights into how these bonds form. The study, published in Evolution and human behaviorhighlights the decisive role played by women.

Why do some male and female primates get along well and form strong bonds, while others don’t? Science has long proposed various theories to explain these bonds, ranging from simple physical attraction to deep-rooted evolutionary processes.

Although these ideas are compelling, most studies of primate bonds have traditionally focused on males as key players, often neglecting the crucial role that females might play in these relationships.

Benefits for both parties

Mapping hundreds of primate observations over the past few decades, an international team of primatologists suggests that these “beneficial friendships” between male and female primates typically develop when both have something to gain from them. For females, it’s about choosing who they mate with. For males, it’s about caring for and protecting their young.

These dynamics are especially important in groups where males cannot simply dominate females and where offspring require care. These bonds are also more likely to form in groups where males are not the leaders and where male care is crucial. Primatologists have mapped hundreds of previous observations of chimpanzees, lemurs, macaques and other species.

“Our results show that these connections are not just about attraction and affection,” Sterck says.

“These bonds are also strategic. Primates, both male and female, unconsciously seek out friendships that provide them with benefits. These benefits can take the form of protection, better access to resources, or the survival of their offspring. For evolution to shape these behaviors, it is not necessary for them to know when or how these bonds will pay off.”

Link change and breakage

The study also shows that the nature of these bonds can change over time. Initially, males tend to groom females more often during mating season, but this dynamic can change. Females may seek support from males to protect their babies while they nurse. A male may initially bond with a female to secure mating rights, and after the female gives birth, she may rely on the male to protect her.

Once the offspring become independent, these bonds often dissolve and both male and female may then move on to other partners.

However, in cases where females provide males with the opportunity to father multiple offspring, lasting bonds are more likely to form. Such stable relationships are common in species such as macaques, baboons, and chimpanzees, where females consistently prefer the same male and males provide ongoing care. These lasting bonds are often supported by mutual benefits, making the continued investment worthwhile for both parties.

Human relations

When it comes to human relationships, the dynamics may be more complex. Additionally, humans typically form exclusive pairs, while both female and male primates tend to mate with multiple partners. But some of the underlying principles of primate bonds apply as well, Sterck’s team says.

“Just like our primate relatives, human bonds often involve a mix of affection and strategic partnership,” Sterck says. “While love and emotional connection are essential, there is also an unconscious element of mutual benefit, whether it’s support, protection, or shared resources.”

Love and affection still play a crucial role in primate bonds, Sterck explains, even though the evolutionary basis for these relationships is based on long-term benefits. “While the drive to form strong bonds may stem from evolutionary advantages, emotions like love and affection are the origin of these bonds. These feelings act as a lubricant, paving the way for the actions and behaviors needed to maintain and deepen these bonds over time.”

Future research

To further explore the extent of their bonding theory in the animal kingdom, Sterck’s team calls for additional research. In particular, they call for additional research on great apes (such as gorillas and bonobos) and so-called New World primates, including tamarins and capuchins, and even on non-primate species that live in permanent social groups, such as wolves and lions.

They also believe that this approach can shed new light on the evolution and dynamics of human couple bonds.