Bonobos are perceived as doing almost nothing but eating, sleeping and especially when in captivity, engaging in sex. That reputation is somewhat overdone, says primatologist Martin Surbeck of the Max Planck Institute for Evolutionary Anthropology: female bonobos in heat actually have less sex than their chimpanzee counterparts in similar condition.
But when not in heat, the bonobos definitely enjoy their encounters, including same-sex. Clearly not all that sexual activity is mating, per se. These amiable apes aren’t particular enough in their sexual expression for their copulation to warrant that definition.
But it turns out that one member of the family does care.
“Bonobo moms will literally drag their sons to ovulating females to get more grandchildren,” report primatologists from the Max Planck Institute for Evolutionary Anthropology in the prestigious journal Current Biology on Wednesday.
Bonobos have been known to have concealed capacities and to rise to the occasion. One female in Israel, irritated beyond reason by her scientific subjugator, revealed an unsuspected ability to fashion weaponry. She made a spear out of a branch and, to drive home the point, tried to stab him with it. He was surprised enough to write a paper about it.
OK, so they’re capable of violence when irked badly enough. But could the females of this chimpanzee species have a sense of posterity? The fact is: males with a mother living in their group have higher paternity success in bonobos but not in chimpanzees, writes the international team. Could this be strategy?
"This is a tricky question, as it is hard to infer what they understand and what not," lead author Surbeck tells Haaretz. "While anthropomorphisms can be misleading, we are in fact closely related to bonobos and therefore share certain feelings and cognitive abilities. They likely know what they are doing, but very likely, they do not know why."
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In sexual beings (which is most beings), the kids get half their genes from their mothers and half from their fathers. Seen from the parents’ perspective, only if their offspring mate successfully, producing progeny, can their lineage continue.
Mammalian mothers tend to have a greater phenotypic influence than fathers: For example, large healthy mothers are likelier to produce large, robust offspring because they give them large amounts of nutrients during pregnancy and lactation. Moreover, rat and monkey studies have demonstrated a strong resemblance between maternal care patterns and those of adopted daughters.
But dragging the son to females in heat is a whole other level of maternal influence.
To be clear, the moms aren't clubbing Son over the head and literally dragging him over to tumescent females. Surbeck aspires to accuracy.
"The relevant behaviours of mothers can be active: fending off other males trying to intervene in sons mating attempts, supporting their sons in the competition for high dominance ranks; or passive - acting as a social passport in that proximity to mums allows sons to remain in the central positions within the social groups resulting in more interactions with other females," he explains. "They do not actively lead their sons to females in term of dragging!"
But yes, a mother will fight a mother over a lady in heat for their sons.
In any case, this was the first time that the impact of the mother’s presence on a very important male fitness trait, fertility, has been shown, says Surbeck. “We were surprised to see that the mothers have such a strong, direct influence on the number of grandchildren they get,” he adds.
This is not some artifact of confinement and boredom. Surbeck and the team, including researchers from Harvard, Tufts, the University of Neuchâtel and more, observed wild bonobos in the Democratic Republic of the Congo, and compared the behavior with wild chimpanzees in the Ivory Coast, Tanzania and Uganda.
Both bonobo and chimpanzee mothers would root for their sons in male-on-male conflicts, but only the bonobo moms “went the extra mile” to aid their sons’ successful copulation.
They did this, specifically, by helping to deflect competing males, heckling other males when they tried to mate, “intentionally” bringing their sons around females in oestrus — and kept potential competition at bay while their sons were mating. Presumably bonobos have a lower embarrassment threshold.
They couldn’t easily miss the action if they wanted to, by the way, as bonobos have big penises compared to most other apes. The gorilla penis averages about 3 centimeters (just over an inch) when erect, while the chimp and bonobo average about 8 centimeters (the human averages around 13 centimeters). Although orgasm is hard to prove in the female, there is thinking that primates in general, and dolphins, are capable of it.
If female orgasm existed in the primordial ape, as well as sexual choice, possibly the females would have selected the males capable of bringing them satisfaction, so they would have chosen the more amply endowed males, up to a point. There is even a theory that bipedalism evolved less in order to pick higher-hanging fruit than for the sake of penile display.
In any case, the researchers also point out that all this can only work because male and female bonobos codominate. If the females were timid subordinates, it wouldn’t work. Also, unlike most species, bonobos don’t necessarily leave the family nest when they mature.
The result was statistically stark: Bonobo males living with mothers were more than three times more likely to have offspring than males not living with mom. This was not found in regular chimpanzees.
By a painstaking process of observation and deduction, the researchers negate the potential “genetic confounding” effect, which means that given offspring do better not because their mother is still alive and helping them out, but because healthy robust mothers could pass on better genes, rendering their offspring fitter.
One issue muddying the waters is that bonobo females have a relatively long interbirth interval of around four years, but they resume sexual cycling (at least the optical signal of it) very shortly after giving birth, says Surbeck. "So they can cycle over several years without conceiving, confusing the paternities of their infants."
There is one point the primatologists and other members of the team have yet to elucidate, if they ever will. Admit it: In humans, women statistically outlive men and the same applies, it turns out, to our friend the killer whale. This is suspected to be because the grandmothers of these species (us, orcas) contribute more to the survival of the kids (“fitness of the lineal offspring”), while the males are out playing darts or eating seals. The life span of the bonobo however remains unknown.
"Bonobos are very long-lived species. They can live 40 to 50 years in captivity," says Surbeck. "There is no place in the wild where bonobos have been observed for so long and therefore we do not know how old they normally get in the wild. Furthermore, we often do not know for sure whether individuals die when they disappear, as we hardly find bodies."