Humans are complicated. Sometimes we hurt each other and sometimes we help each other. In the ongoing effort to understand where those competing instincts come from, anthropologists often turn to our closest living relatives — chimpanzees and bonobos. Yet these two species of ape are very different. The stereotypes hold that chimpanzee society is rife with hierarchy and aggression, and bonobos, by comparison, are peaceful proponents of free love. That's oversimplified. Within a group, chimpanzees can be peaceful. And bonobos might be capable of aggression. Humans are a "mosaic" of both. The challenge for scientists is to figure out what elements of human behavior exist in either ape, thereby teasing out which traits are purely cultural and which have biological roots.
New evidence published this week in Scientific Reports builds on earlier work and suggests that the capacity to help a stranger at no benefit to oneself cannot be claimed by humans alone, as we once thought: Bonobos do it, too. They will help a stranger get food, forgoing food themselves, especially if they then get the pleasure of that stranger’s company. And they don’t have to be asked either. (In apes, that looks like reaching out an arm to beckon for help.) Like us bonobos have their limits, though. If the costs are too high—they lose highly desirable food, say, and there is no reward—they stop helping. “Basically, it tells you that for bonobos, hanging out with strangers is really rewarding, and being nice to them does not have to be altruistic,” says anthropologist Jingzhi Tan, the new study’s lead author. He conducted the study with Brian Hare and Dan Ariely of Duke University, working with bonobos who live at the Lola ya Bonobo sanctuary in the Democratic Republic of Congo.
I spoke with Tan, now a postdoctoral scholar in the Department of Cognitive Science at the University of California, San Diego, about the implications of this work, and why it might be good news.
Why study helping behavior in bonobos?
In the anthropology department, at the end of the day, we’re trying to understand humans. One of the major puzzles in human evolution is the origin of altruism. Helping someone that we don't know at all is often considered one of the most extreme forms of altruism. Yet it happens frequently. The assumption is that helping strangers must be altruism because there’s no way for them to pay you back, and that this makes us unique because no other animals would be able to do this. So then there are a lot of hypotheses saying it must be culture, it must be social norms, it must be language that makes this possible.
We set out to test this. If this is unique to humans, we should not see bonobos help a stranger. Chimps help each other and work together, but they only do that with someone they know. They are xenophobic. Honestly, in humans, culture, language and social norms are still playing a really important role in shaping our prosocial behavior, but the real question is: Do we need these things to [push us to] help or share with strangers? The main finding of the work is that bonobos can do it. They are xenophilic, they like strangers. So, you don’t need culture or language to have at least some basic form of this kind of behavior.
Does it mean the urge to be altruistic is more biological than cultural?
We use the word “predisposed.” You have this tendency to do something. It’s not taught, it’s not learned. And then, of course, your experience or how you are educated would have a tremendous impact on how it plays out. Some would be extreme altruists and some would be really selfish. But part of our nature would be to be nice to strangers.
You also experimented with contagious yawning, when one individual yawns and triggers yawning in another individual. Can you tell me about that?
We took advantage of this phenomenon to measure whether bonobos react to complete strangers in a positive way or in a negative way. Contagious yawning is a very reliable way to tell the quality of social bonds. In humans and in bonobos, the higher the quality of the social bond with someone else, the more likely you’re going to yawn with them. We don’t know why. It could be a stronger emotional connection or more attention. What’s interesting is that there’s a chimp study showing that the chimps only yawn with the in-group, not with the out-group.
We put the bonobos in a very similar context and showed them videos of their group members and videos of completely unknown bonobos from the Columbus Zoo. We see a similar response—contagious yawning—between someone they’ve never met versus someone from their own group. It’s a really different result from the chimpanzees.
Does all this give us some hope? Not to be too simplistic about it, but it seems that our country is currently divided into chimps and bonobos — those who fear strangers and those who don’t.
I cannot agree more. We all want the kind of society where you have diversity and peace and tolerance. Right now, if you don’t consider the role of biology, then the only tool you have [to encourage that behavior] is through culture and education. If we know that it’s part of our nature to do that, then how do you trigger this kind of predisposition to show up more often in real life? We don’t have to only use nurture as a tool; we can use nature as well. Combining the two of them would be even more powerful.