By the age of three months, human babies can already follow Mr. Rogers' advice to "look for the helpers." In fact, human infants naturally show a strong preference for individuals who help rather than hinder others. Now, a study reported in Current Biology on January 4 finds that the same cannot be said of bonobos, one of humans' two closest relatives. While bonobos are similarly adept in discriminating helpers from hinderers, they show the opposite bias, consistently favoring hinderers over helpers.
The findings suggest that humans' preference for helpers evolved only after our species diverged from other apes. This preference may have provided the foundation for the development of more complex features of human cooperation, the researchers say. The evidence also suggests that bonobos might prefer hinderers because they see them as more dominant. In primate society, it pays to be dominant and have dominant allies.
"We were surprised in that many have characterized bonobos as being the most cooperative, 'hippie' ape," says Christopher Krupenye of Duke University. "Our experiments show that the issue is much more nuanced. Bonobos are highly socially tolerant in food settings and help and cooperate with food in ways that we don't see in chimpanzees. However, dominance still plays an important role in their lives."
The new study by Krupenye and Brian Hare, senior author of the study, was inspired by an earlier study reported in 2007. It showed that young human infants already prefer helpers. "It was striking and unexpected and suggested that these sorts of motivations may be really central to humans' unusually cooperative nature," Krupenye says.
In the new study, they wanted to find out whether the motivation to prefer helpers might be unique to humans. Because of the friendly reputation of the highly endangered bonobos, it made sense to start by looking at them. The researchers conducted their studies at Lola ya Bonobo, a sanctuary for orphaned bonobos in the Democratic Republic of the Congo.
The researchers showed bonobos two-dimensional animated shapes that helped or hindered each other much as the earlier study did with infants. They then evaluated the bonobos' preference for one character or the other by watching which paper cutout character (placed atop a slice of apple) they reached for first.
In additional experiments, bonobos were given a choice to interact with unfamiliar humans they'd observed either helping or hindering. In every case, bonobos showed an ability to differentiate helpers and hinderers. Surprisingly, however, they showed a preference for hinderers every time. A final experiment suggested that the bonobos' preference for hinderers might be driven by attraction to more dominant individuals.
The findings in bonobos raise the possibility that one of the key motivational foundations of humans' uniquely cooperative nature -- which is present early in infancy -- may be unique to humans among the apes, the researchers say.
"Bonobos exhibit a high level of social intelligence, tracking others' social interactions and evaluating novel social partners based on these observations," Krupenye says. "However, what motivates social preferences may be fundamentally different in bonobos and humans."
Krupenye says that they continue to explore social preferences and social evaluation in bonobos, trying to understand what types of social information they track and what motivates their preferences. They also plan to conduct similar studies in chimpanzees.
Materials provided by Cell Press. Note: Content may be edited for style and length.
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