How Deep Is Your Love? Human Morality and the Question of Altruism Among Non-human Primates.

by Kenneth W. Krause.

Kenneth W. Krause is a contributing editor and “Science Watch” columnist for the Skeptical Inquirer.  Formerly a contributing editor and books columnist for the Humanist, Kenneth contributes regularly to Skeptic as well.  He may be contacted at

I looked into his eyes. It was like looking into the eyes of a man. And the message was: Won’t anybody help me?—A zoo visitor who had rescued a chimpanzee from drowning in the enclosure’s moat.

The depth and instinctual force of human altruism is a complicated matter.  Today’s leading anthropologists, primatologists, and comparative psychologists—together with their ever-enigmatic primate subjects—are slogging it out in laboratories around the world.  Will apes and monkeys, our nearest evolutionary relatives, think to bestow charity upon other beings, and, if so, under what specific circumstances?  As the experiments progress, the debate grows ever more contentious.

Some say that altruism is primarily a cultural phenomenon, unique to humans.  Others insist that its roots extend much deeper, past the common ancestors of humans and chimpanzees that flourished in Africa some six million years ago.  If the latter is true, goodness can be characterized as a given, at least to some predictable and very comforting extent.  If not, human morality might be only a veneer—a thin gauze nearly soaked by the gaping, untreatable wounds of greed and insensitivity, or something to that general effect.

So given the metaphysical stakes, it should come as no great surprise that the possibility of so-called “other regarding preferences” in non-human primates is among the hottest of hot scientific topics.  For many years, the clear consensus had been that humans were the only genuinely altruistic species on earth.  On June 25, 2007, however, the journal Nature reported gathering evidence that “we might not be alone.”  Similarly, in January of this year, Discover magazine summarized the first experimental support for “spontaneous altruism in chimpanzees, toward both non-related chimps and humans.”

These articles described recent methodological breakthroughs made by Felix Warneken, a leading researcher at the Max Planck Institute of Evolutionary Anthropology in Leipzig, Germany.  To that point, experimenters had mostly used food rewards as a means of probing the prosocial tendencies of chimpanzees, and the results had been largely unimpressive.  Journal headlines had carped, for example, that “chimpanzees are indifferent to the welfare of unrelated group members” (Nature, 2005, 437, 1357-1359), and that “self-regard precludes altruism and spite in chimpanzees” (Proc. R. Soc. B, 2006, 273, 1013-1021).  But Warneken decided to break ranks with his colleagues and confront the question from an entirely different angle, judging that the nutritional imperative might be entirely too strong for chimps to resist.

By 2006, he had tested three young chimps’ desires to assist their human caretakers in obtaining useful objects just beyond their beckoning reach—ballpoint pens, for example (Science, 311, 1301-1303).  Warneken’s subjects performed admirably, even without the possibility of reward.  And by 2007, he had designed two additional experiments, each of which applied improvements to his innovative “instrumental helping” paradigm (PLoS Biology, 5(7), e184).

First, he replicated the 2006 study—this time using unfamiliar human partners—and got similar results.  Then, he positioned his subjects to watch unfamiliar partner chimps, or “conspecifics,” as they struggled to open a locked door.  Fully unaware that food had been placed beyond that door, the subjects chose to aid their partners by freeing the chain attached thereto nearly 80 percent of the time.  Thus, in all three studies, Warneken’s animals had demonstrated an eagerness to indulge others, even when doing so required them to expend a little extra effort.

When I asked Warneken about these intriguing results, he emphasized that food sharing “is only one type of potentially altruistic behavior,” and, indeed, that food exchange might not be the greatest method of assessing altruism, given that chimpanzees are generally hyper-competitive over food.  In other words, researchers relying on the erstwhile paradigm may have set the altruism bar a bit too high, even for our closest cousins.

But not according to Frans de Waal, perhaps the most accomplished primatologist on the planet—and certainly the most celebrated one since the pop-media heyday of Jane Goodall.  In a primer to Warneken’s 2007 study, de Waal remarked of previous trials involving chimps and food techniques that “all that these experiments really showed was that humans can create situations in which apes focus on their own interests” (PLoS Biology, 2007, 5(7), e190).  After all, de Waal pointed out, although human bargain hunters will mercilessly trample their fellow holiday shoppers to hoard insanely cheap microwave ovens and televisions sets, that doesn’t necessarily mean we are completely or chronically indifferent to one another’s welfare.

Although he doesn’t deny that kinship and reciprocation play major roles in the prosocial tendencies of primates, de Waal proposes a more philosophically nuanced analysis that distinguishes a behavior’s ultimate from its proximate cause.  The former might explain why actions are favored by natural selection, while the latter illuminates the psychological or physiological mechanisms triggered by animals’ present situations.  de Waal offers sex as an especially helpful and engaging analogy.  Without the slightest interest in reproduction—sex’s ultimate cause—men and women crave physical intimacy and carnal knowledge of one another’s nearly irresistible bodies simply for the immediate emotional and physical ecstasy of it all.

Once evolved, in other words, behaviors can rebel against their Darwinian overlords, seizing motivational autonomy from their ultimate goals.  Thus, de Waal argues, “empathy evolved in animals as the main proximate mechanism for directed altruism,” and it is empathy—not self interest—that “causes altruism to be dispensed in accordance with predictions from kin selection and reciprocal altruism theory” (Annu. Rev. Psych., 2008, 59, 279-300).  Having originated in parental care, empathy in general is as old as the storied mammalian class itself.  When coupled with the perspective-taking abilities intrinsic to a very few large-brained species, however, empathic instincts take on an entirely different character, producing spontaneous, yet intentional, other-regarding responses.

De Waal and Sarah Brosnan, de Waal’s student at Emory University until very recently, became famous in anthropological circles for their token-exchange experiments revealing aversion to inequity in both brown capuchin monkeys and chimpanzees (Nature, 2003, 425, 279-299, and Proc. R. Soc. B, 2005, 272, 253-258).  Importantly, the team’s monkeys appeared to be sensitive only to their own relative disadvantages while their chimps’ reactions depended on each individual’s social history—members of older, more tightly-knit groups tending to be more accepting of iniquitous outcomes.

De Waals’ most recent token-exchange experiment, however, was designed to more directly probe the alleged predilection for altruism in capuchins (Proc. Natl. Acad. Sci., 2008, 105, 13685-13689).  Subject monkeys were given two simple options. They could selfishly reward only themselves or, more philanthropically, both themselves and their hungry partners.  In the end, they tended to choose the prosocial option regardless of condition, but did so more consistently when their partners were either familiar or genetically related.  Because his subjects were predominantly other-regarding in all situations, and without fear of belated group reprisals, de Waal again inferred that the underlying impetus for capuchin prosociality had to be empathetic—as predicted by his theory of motivational autonomy.

But other, perhaps less celebrated, researchers have arrived at very different conclusions.  In 2007, Keith Jensen’s team, also at the Max Planck Institute in Leipzig, set eleven enthusiastic animals loose on a chimp-friendly adaptation of the legendary ultimatum game (Science, 318, 107-109).

In the game’s standard human version, of course, two unfamiliar players are assigned the roles of proposer and responder.  The proposer provisionally receives a gift of money and decides whether and how to divide it with the expectant responder.  The responder, in turn, resolves whether to accept the proposer’s offer.  If she rejects it, neither player receives any money whatsoever.  With those rules in mind, proposers tend to graciously volunteer 40 to 50 percent of the sum and responders routinely reject offers of less than 20 percent.  In other words, human responders are sensitive to unfairness and will punish inconsiderate proposers—even at a significant cost to themselves—and human proposers, realizing this, tend to make relatively fair offers that are more likely to be tolerated.

According to Jensen’s results, by contrast, chimpanzees play the ultimatum game more in keeping with the canonical economic model of pure self-interest.  Using a relatively uncomplicated apparatus featuring ropes, rods, and baited trays, Jensen discovered that his chimp proposers—supposedly accustomed to the apparatus and, thus, familiar with the game’s uncomplicated rules—tended to make coldly iniquitous offers, and, conversely, that his chimp responders were apt to accept all nonzero tenders, ostensibly without umbrage.

More recently, Jennifer Vonk, along with Brosnan and several others, published their study of eighteen chimps at the University of Louisiana’s Cognitive Evolution Group laboratory (Animal Behavior, 2008, 75, 1757-1770).  In her introduction to the study, Vonk commented on de Waal’s “anecdotal” accounts of primate prosociality, cautioning her readers that “conclusions about chimpanzees’ capacity for empathy and other-regarding sentiments rests on subjective interpretations of behavior and have not been subjected to systematic analysis.”

She also referred to and, indeed, credited Felix Warneken’s instrumental helping experiments, but carefully distinguished them from her studies, which had been calculated to address Warneken’s concerns about food as an experimental medium.  In two separate trials involving two different apparatuses—one featuring ramps, the other trays—Vonk’s subjects were provided opportunities either to reward only themselves with fruit, to reward only their conspecific partners, or to furnish food for both themselves and their partners.  Crucially, the chimps were allowed to make their fateful choices either before or after consuming their own rewards and, thus, according to Vonk, “avoiding the possibility that obtaining food for themselves distracted them from obtaining food for their partners.”

Following the training, and then all of the rolling, pulling, and consumption of tasty treats, Vonk’s team finally surmised that chimpanzees do not reliably take advantage of low-cost opportunities to nourish their hopeful peers.  In nearly every case, the presence or absence of a partner conspecific had no effect on the subject’s decision to send fruit to the other animal’s enclosure.  Vonk’s subjects seemed wholly indifferent to the desires of others.  Chimpanzee behavior, she concluded, “is consistent with standard evolutionary models based on kinship and reciprocity.”

But could it be that some chimps and monkeys—like some humans we might know—are more callous or self-absorbed than others?  Every experiment, after all, tests only a very limited number of individuals.  Maybe Jensen and Vonk just happened to assemble a group of stingy, egocentric misers, and Warneken a rare cache of Good Samaritans.  “Normally, negative results would be largely ignored,” de Waal told me, “but the negative results on animal altruism are hyped over and over” because they support the dominant “strong reciprocity” school of thought that insists on human uniqueness.

Now Assistant Professor of Psychology at Georgia State University, Sarah Brosnan remains fundamentally ambivalent about the sticky issue of primate altruism.  On the one hand, her personal encounters with primates inform her that both apes and monkeys at least seem other-regarding.  On the other, she admits that to this point her intuitions remain largely unsubstantiated by solid evidence.  Even so, Brosnan is confident of at least two things.  First, despite her and Vonk’s findings in Louisiana, chimp altruism is “more likely to be elicited in contexts which do not involve food,” and, second, it is “much more likely to be based on emotion and relationships than on cognitive calculations.”

Unsurprisingly, Keith Jenson endorses a more objective and skeptical attitude.  Like de Waal, he suspects that even chimpanzees lack the mental capacity for delayed, calculated reciprocity.  But he also criticizes de Waal’s reliance on subjective evidence of primate altruism and his “somewhat contentious” use of the term “empathy.”  In the end, Jensen believes that kinship is usually, if not always, the dominant underlying mechanism of animal prosociality, and, thus, that empathy and other-regarding preferences “only emerged somewhere during human evolution.”

The current preponderance of hard, empirical support appears to weigh-in on the side of reservation, despite recent media exuberances.  Then again, as de Waal has been quick to point out, non-human primates have been known to achieve extraordinary, if exceptionally rare, prosocial performances that if committed by humans would doubtless be characterized as nothing short of heroic.

One chimpanzee in particular is known to have overcome its species’ intense dread of water in order to save a drowning infant chimp’s life—only to surrender its own.  I can no more than speculate on what the Midwestern farmer would have done all those years ago had he been unable to tread water.  And in August of 1996, a valiant female gorilla named Binta Jua was actually filmed as it rescued a three-year-old boy who had fallen eighteen feet into the primate exhibit at Chicago’s Brookfield Zoo.  Binta quickly whisked the boy away to a safe location, cradling and pampering him there, before finally delivering him to the zoo’s dumbfounded and no doubt nervous staff.

The skeptics would do well to develop and refine their explanations of these amazing behaviors, just as the champions of primate altruism should be set to the task of providing empirical evidence for their predominantly philosophical and intuitional hypotheses.  Either way, human morality is no mere act; clearly, it is the evolutionary extrapolation of our innate, cooperative tendencies.  The question, rather, is one of degree—how deep are our moral foundations, and how much more can we reasonably expect from one another?


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