To most human males, the thought of your mother anywhere near your sex life is probably horrifying. Not so for the bonobo, one of our closest primate relatives. A new study confirms that hanging out with mom boosts male bonobos' chances of getting intimate with a fertile female.
The study found that when their mothers are around, low- to mid-ranking bonobo males get more opportunities to mate. Mothers facilitated sons' presence in their social circle so they were able to interact with more females, and also chased away rival males who might try to break up their sons' blooming relationships.
The mothers aren't just busybodies, say the researchers. In fact, taking an active interest in their sons' love lives helps mothers pass on their own genes.
"If they support their sons, they can have more grandkids," study researcher Martin Surbeck, a biologist at the Max Planck Institute for Evolutionary Anthropology in Germany, told LiveScience.
Bonobo mama's boys
As any newlywed can tell you, parental interest in offspring's reproduction is common. Orcas are known to form strong mother-son bonds, and according to a study published in August in the journal Nature Communications, being born to a high-ranking mom gives male hyenas a reproductive boost later in life.
In primates, mothers have been shown to improve the survival of their daughters' offspring. But mother-son bonds are harder to measure, because most primate males leave their mother's side at puberty. Bonobos, a cousin to chimpanzees, are an exception. Bonobo communities are female-dominated, and males stick with their mothers in adulthood.
Researchers have long known that the status of bonobo males is linked to the status of their mothers, and field observations suggested that moms were taking an active role in facilitating their sons' mating, said Surbeck. To figure out the maternal role, he and his colleagues used DNA information to tease out the relationships between the bonobos in their field area at Salonga National Park in the Congo. Then they observed the bonobos over a 10-month period, watching how often they fought, mated and became fertile.
They saw that while the primates split into different "parties" during the day, sons stuck with their mothers between 81 percent and 92 percent of the time. When moms weren't around, the dominant male was responsible for about 41 percent of sexual encounters with fertile females. But when the mothers of low-to mid-ranking males were present, that proportion dropped to 25 percent. In other words, moms kept the dominant male from monopolizing the most fertile females, allowing their own sons to mate, too.
Sometimes, the moms interfered, chasing unrelated males away from females or backing up fights involving their sons. Other times, they stood guard while their sons mated, keeping competitors at bay.
But in large part, the mom's role may be more like that of a matchmaker. Since females have lots of social status in bonobo communities, Surbeck said, a mother's presence allows a son to play a more central role in the group. Being in the center of the social group means more interactions with females and more opportunities to mate.
The study, published this week in the journal Proceedings of the Royal Society B, "confirms largely what we've known for a long time" about the importance of mothers in bonobo communities, said Jo Thompson, the director of the Lukuru Wildlife Research Project in the Democratic Republic of the Congo.
Thompson, who researches bonobos but was not involved in the current study, said the research raises new questions about the influence of a mother's social rank on her son's success, as well about how other family members, like brothers, might influence mating. She also warned that while the current study showed low- and mid-ranking males got to mate more with fertile females when their moms were present, it didn't investigate whether they actually had more offspring.
"This is a good solid study that continues to build on the knowledge we have, and leads to more questions," Thompson said. "The next step is where we really get interesting."
Studying bonobos is important for conservation reasons, as the animals are threatened by habitat loss and poaching, said University of California Los Angeles anthropologist Joan Silk, a primate researcher who was not involved in the study. But because humans share an evolutionary ancestor with bonobos, the studies may also give us hints about our own evolutionary background, Silk said.
"Seeing both chimpanzees and bonobos gives us an idea of the range of possibilities of our ancestors'" behavior and social structure, Silk said. "They help us imagine what early human ancestors might have been like."