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Frans de Waal Answers Your Primate Questions

Frans de Waal

We recently solicited your questions for primatologist Frans de Waal. Of all his accomplishments, one of the greatest has been his ability to so well communicate his scholarly findings to a wide audience. Here is one compelling piece of advice he offered on that subject: “Keep the reader interested, whatever it takes, so long as you don’t violate the truth.”

His answers below, which openly discuss (inter alia) how polygamist sects mimic the mating systems of animals, why bonobos eat after sex, and his opinion of “God-questioning rants,” definitely stay true to his philosophy. He also shows a keen understanding of economics when discussing how monkeys, just like some people, exhibit “inequity aversion” — a sure sign of irrationality if profit-maximizing is the goal.

Thanks to Frans for his fascinating answers, and to all of you for your very good questions.

Q: Do primate species other than bonobo monkeys use sex as a form of communication/bonding/intimacy vs. purely procreational purposes?

A: Bonobos offer the best example of non-reproductive sex. They use sex at the drop of a hat for reasons that, most of the time, seem social — such as during a reconciliation after a fight, or when they anticipate food competition. They use sex to diffuse tension: after the sex they share the food. Bonobos are our closest animal relatives together with chimpanzees.*

How much bonobos differ from chimpanzees was highlighted by a recent experiment in which apes were presented with a platform that they could pull close by working together. When food was placed on the platform, the bonobos clearly outperformed the chimpanzees in getting a hold of it.

The presence of food normally induces rivalry, but the bonobos engaged in sexual contact, played together, and happily shared the food side by side. The chimpanzees, in contrast, were unable to overcome their competition.

Outside bonobos, there are many other animals that engage in sex even if reproduction is impossible, such as when the female is pregnant, or between members of the same sex. Also here, the sex serves a bonding function, or to signal dominance. So, the idea that sex is intended for reproduction and should therefore be used exclusively for reproduction (an argument used by the Catholic church against condom use) is incorrect for many animals, as it is for our own species.

* Bonobos and chimps are not monkeys, but apes. Apes are large primates with large brains, no tails, flat chests, and shoulders. Monkeys are smaller, have tails, and often a more protruding face (snout). Humans are obviously more like apes than like monkeys.

Q: Does religiously motivated rejection of evolution (e.g. creationism) ever get in your way when working?

A: I don’t experience this kind of resistance in science, in which evolutionary theory is obviously the dominant paradigm. Creationists sometimes try to create the impression that lots of scientists have their doubts about the theory, but I have yet to meet such scientists. I’d be surprised if more than 0.1 percent of active research biologists have such doubts.

When I came to this country, over twenty-five years ago, I was amazed that creationism was still taken seriously, and assumed that it would blow over. It never did, of course. I can’t help but look at it as a left-over of a medieval mind-set unresponsive to overwhelming counter-evidence.

At the same time, I must say that I don’t think the recent wave of God-questioning rants have helped much. They have polarized the issue, whereas in my mind it is eminently possible to look at religion as a collective value system and at science as telling us how the physical world operates. Even though I am not religious myself, I think the conflict between science and religion is unnecessary and overblown.

Q: Is yours the lab that did the grape vs. cucumber study? The monkeys got either a grape or a cucumber for doing a task …

A: Yes, together with Sarah Brosnan, we did a study in which capuchin monkeys received either a grape or a piece of cucumber for a simple task.

If both monkeys got the same reward, there never was a problem. Grapes are by far preferred (as real primates, like us, they go for sugar content), but even if both received cucumber, they’d perform the task many times in a row.

However, if they received different rewards, the one who got the short end of the stick would begin to waver in its responses, and very soon start a rebellion by either refusing to perform the task or refusing to eat the cucumber.

This is an “irrational” response in the sense that if profit-maximizing is what life (and economics) is about, one should always take what one can get. Monkeys will always accept and eat a piece of cucumber whenever we give it to them, but apparently not when their partner is getting a better deal. In humans, this reaction is known as “inequity aversion.”

I actually don’t think the response is irrational at all, but related to the fact that in a cooperative system, one needs to watch what kind of investment one makes and what one gets in return. If your partners always ends up getting a greater share, this means that you’re being taken advantage of. So, the rational thing to do is withhold cooperation until the reward division improves.

This holds an important message for American society which is becoming less fair by the day.

The Gini-index (which measures income inequality) keeps rising and is now more in line with that of third-world countries than of other industrialized nations. If monkeys already have trouble accepting income inequality, you can imagine what it does to us. It creates great tensions within a society, and we know that tensions affect psychological and physical well-being. Some attribute the dismal health statistics of Americans (now #42 in the world’s longevity ranking) to the social frictions of an unfair society (see Richard Wilkinson, 2005: The Impact of Inequality).

Q: Do promiscuous gay men and bonobos have anything in common?

A: Bonobos often engage in sex with same-sex partners, but they’re not gay in that they also have sex with the opposite sex. They’re “bi.” They seek sex often for social reasons, to reduce tensions, and to form friendships. I am not sure that this also applies to human gay promiscuity, or whether the latter is purely pleasure-oriented.

Q: Do you think that many of the results you and your collaborators have found would be similar if the experiments were done in the wild?

A: The relation between fieldwork and captive work on primates is an important one.

True, our grape-versus-cucumber test cannot be conducted with wild monkeys for the simple reason that they’re not used to receiving food from humans. It is unlikely, however, that the striking psychological mechanism that we observed, leading to great agitation in the monkeys, comes out of the blue.

As said, I look at it as evolved in the context of cooperation, mainly to ensure commensurate rewards for efforts. So, I expect the same inequity aversion in dogs and wolves, but not cats (which are solitary hunters, and shouldn’t care much about what others get).

Cooperation has been observed among wild capuchins. They sometimes work together to capture (and eat) giant squirrels or coati pups. After the hunt, they enjoy the spoils — which is where reward division comes in.

The fact that capuchins are capable of cooperation hints at the right evolutionary impetus for inequity aversion.

I know, in fact, of no untrained skills discovered in captivity that have never been found in the same species in the wild. Tool-use, for example, was first known of zoo apes, and everyone said that this doesn’t count — until of course wild apes also were shown to use tools.

Or, take reconciliation behavior, which I discovered in a zoo colony of chimpanzees — and everyone said that obviously wild primates wouldn’t do such a thing. But we now have data on close to thirty different primates that reconcile after fights (and also non-primates, such as dolphins and hyenas), and the evidence includes wild monkeys and apes.

I do believe, however, that captive studies can never replace studies in the field. They just have different insights to offer, such as with the studies of chimpanzee cultures.

Many chimpanzee groups in Africa have their own unique traditions, such as nut-cracking or social customs. The field workers speculate they learn these behaviors from each other through imitation. They can’t prove this, however. This is where captive studies come in, as we are capable of testing what apes can learn. Our studies strongly support the field work in that we have shown apes capable of picking up new skills from each other.

Q: Are baby monkeys as helpless and dependent on their mothers (or other adults) as human babies?

A: All primates are characterized by a long dependency — in monkeys, such as macaques and baboons, usually the first two years. But even after this, the bond is maintained, and the mother provides support and grooming.

In the apes, the period of dependence is quite a bit longer. Nursing lasts for four, sometimes five years, and the mother carries her young first on her belly, then on her back. Given the load this represents, she can’t have too many offspring. So, she has one baby at a time, and the inter-birth interval in the wild is five or six years. Young chimpanzees become relatively independent by eight, but aren’t considered adult until they are over twelve years old.

Q: Possibly the dumbest question: have you observed primates engaged in incestuous sexual behavior? if so, is it ignored, rewarded, or punished by the social group?

A: Very timely question. Whereas I look at the polygamist sect in Texas with intrigue, as they seem to mimic the mating system of quite a few animals (sending out young males so that the dominant males can freely reproduce with lots of females), the incestuous man in Austria doesn’t fit anything I know about primates, because all animals have ways of avoiding inbreeding. There is, in fact, very little inbreeding even at zoos, where sometimes daughters grow up with males who could be their fathers.

The general rule in primates is that one sex or the other leaves the group at puberty. In many monkeys, the males leave and seek another group. With apes (and overwhelmingly in human societies, too), it are the females who leave. You can imagine that this takes care of a lot of inbreeding opportunities, as the migrants go find groups where they meet unrelated members of the opposite sex.

On top of this, animals follow the so-called Westermarck effect, which is also thought to apply to humans. The rule is that individuals who grow up together develop sexual aversion for each other. Siblings or mother-son combinations just don’t have a great desire to have sex. Westermarck formulated this idea long ago, and it has been tested with many animals, and generally holds up. There is also evidence of Kibbutz and Chinese marriage data that in humans, too, individuals who grow up together, even if they’re unrelated, avoid sexual relations.

Q: How much does culture vary between chimp troops? If a chimp moves from one troop to another, will it teach the new troop anything of its old culture?

A: There are instances in the wild of female chimpanzees entering a new community from the outside, and bringing new knowledge with them. They don’t bring radical change, but usually small steps, such as the female knowing a certain nut that can be eaten and that her host community doesn’t touch.

Q: Can any primate can be taught any sustained, rhythmic, gravitationally constrained movement behavior lasting for 10 seconds to 1 minute without missing a beat? (The speed must be at the rate of 450 to 550 milliseconds per step.)

For example: jumping up and down in place, marching in place, stepping 2 steps up onto then 2 steps down off of a stool.

Do any primates show the “stepping reflex” present in neonates?

A: This question is a bit too precise for me to answer, but of course many animals have an excellent sense of rhythm, since this is part of their locomotion.

Look at the regular wing-beat of many birds (or butterflies, for that matter). A large animal, like an elephant, could never move as elegantly as it does if it didn’t coordinate the rhythm of its four legs carefully, which requires rhythm.

Chimpanzees drum, and they can do so in a very nice and steady rhythm. They usually don’t do so for long, but occasionally they get really into it and keep hitting a hollow object for minutes on end until it drives everybody crazy.

Perhaps the best video of a bird with a great sense of rhythm is the one of Snowball, the cockatoo, who seems to have an extraordinary sense of rhythm. Pronking or stotting Thompson gazelles also come to mind: they jump up and down in a display that is believed to signal their health to potential predators, who will go look for easier prey.

Q: What did you learn from Desmond Morris?

A: Great question. Desmond Morris is the most underrated behavioral biologist (ethologist) of his generation. His books have shaped the view of many, because he openly discussed, with great humor and flair, the human-animal connection before we had sociobiology, evolutionary psychology, and the like.

He also formulated ideas that others have adopted (stolen?) without any reference to him, such as that human talking is a bit like primate grooming, or that the human family arose so as to reduce competition among males, allowing them to go hunt together in the knowledge that each one would have a mate to return to.

These are very interesting ideas, albeit a bit untestable, but the main point is that Morris opened up the discussion about human origins and how they relate to animal behavior. He did all of this in a way that people understood and wanted to read.

But being such a popular “vulgarizer,” real scientists sometimes look down upon him.

The history of his popularity is interesting. I heard from his publisher that Morris had written many books before The Naked Ape, his giant 1960’s best seller (with a for-those-days very provocative title and cover). But those previous books hadn’t done too well.

He would entertain visitors at the London Zoo with a popular overview of comparisons between human and animal behavior. Everyone thought it was funny and deep and informative, and after his publisher had heard him speak, he said, “There’s your book!”

He wrote it in three months, I believe, because it was already all in his head.

I admire the guy, because it took guts to write what he wrote. As a student, I learned about his book because my professors kept warning us not to read Desmond Morris. The result was, of course, that we felt we had to.

What I learned: Keep the reader interested, whatever it takes, so long as you don’t violate the truth.

Q: I recently learned that there is a simple, funny test that helps to find out whether a toddler is self-conscious or not; simply put a red dot on his or her nose in front of a mirror and see whether or not the child tries to wipe it off. Now of course, that’s only self-consciousness; it doesn’t tell you how aware the child is of others and of the differences between those others and itself. This made me wonder, how self-conscious are primates?

A: Mirror self-recognition is tested this way. Children pass this test between 18 to 24 months, and the only animals thus far which have passed are the four great ape species (including chimpanzees), dolphins, and elephants. We conducted the elephant test at the Bronx zoo with a jumbo-sized mirror, and put some of the videos of this experiment on the web.

Q: Do you have any thoughts, personal or professional, on the so-called aquatic ape hypothesis of human evolution? (Posted by Sir Alister Hardy.)

A: It’s an honor to receive this question from you, who developed the hypothesis. I find that the idea has many intriguing elements to it, such as the subcutaneous fat layer and diving reflex that marks us humans. But until I see overwhelming evidence of human ancestors who lived near the water edge and survived mainly on aquatic plants and animals, it remains a hypothesis.

Finding one or two such settlements would in fact be insufficient, because for water to have been a major evolutionary force in the origin of humans, I’d guess we would need to find that during a certain time period this was the only way our ancestors survived.

Thus far, the evidence isn’t there. But perhaps you feel that the paleontologists haven’t been looking in the right places?

Long ago (in Peacemaking among Primates, 1989), I made some tongue-in-cheek speculations about bonobos as aquatic apes. They are the only apes to enter water voluntarily, seemingly enjoying it. There were rumors at the time that they’d walk bipedally into shallow rivers, which is a logical thing to do if you want to keep your head above the surface.

In recent years, I have heard few such stories, so perhaps they were exaggerated. But there is in fact footage of such behavior at a Belgian zoo.

For me the aquatic ape theory is not dead, but in great need of further evidence.

Q: Can an animal be “immoral” or are they “amoral”?

A: That’s a BIG question, which I can’t answer in a brief note. An organism can only be immoral if it is part, and adheres to, an agreed-upon system of morality, as we do. I don’t believe that chimpanzees, or other nonhuman animals, are moral beings in the sense that we are.

But to call them amoral isn’t correct either. Amoral means a total absence of morality, and it is obvious that the building blocks of morality (empathy, sympathy, cooperation, social rules) can be found in animals other than us.

The view that the natural world is “amoral” comes from Charles Darwin‘s contemporary, T. H. Huxley, who felt that nature could never have produced human morality. He saw nature as inherently nasty.

I strongly disagree with this bleak view, as did Darwin himself (in The Descent of Man), but Huxley’s views are unfortunately still very much with us. I wrote an entire book to counter them: Primates & Philosophers.