Why humans may have more in common with chimps than we thought

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• Judy Woodruff:

  You often hear about studies of animal intelligence and behavior. But tonight, we explore a different question — what can we learn about ourselves from studying the inner lives of chimpanzees?

  Jeffrey Brown talked to primatologist Frans de Waal about his new book exploring the emotions of primates.

• Frans de Waal:

  You see the rain face? I always see disgust in their faces when it rains.

• Jeffrey Brown:

  Call it the "rain face" — a look of disgust, in the midst of a downpour. It's an expression of emotional life in animals as well as people, according to primatologist Frans de Waal.

  So, they're venturing out, huh?

• Frans de Waal:

  Yes.

• Jeffrey Brown:

  In the mud, in the rain.

• Frans de Waal:

  Well, it is because of food —

• Jeffrey Brown:

  We all had our "rain faces" on during a recent wet visit to the Yerkes National Primate Research Center, part of Emory University, outside Atlanta, Georgia, where de Waal has worked for nearly three decades.

• Frans de Waal:

  They don't like to get their hands wet, you know? You see that?

• Jeffrey Brown:

  And helped change the way we think about animals and humans.

  So, you don't buy the idea that we could say disgust is only a human emotion?

• Frans de Waal:

  No. I'm not sure that there are any uniquely human emotions. We may have a wider applicability of these emotions, and they may be more sophisticated, but they are not fundamentally different. I haven't seen anything of a fundamental difference in the emotions.

  I have known many alpha males in life, chimpanzee alpha males.

• Jeffrey Brown:

  De Waal is renowned for his work on animal intelligence — experiments that show the ability to use tools, plan, cooperate, and more. He's author of a dozen books, the last titled, "Are We Smart Enough to Know How Smart Animals Are?"

  Now, he's focused on their emotional life.

• Frans de Waal:

  All my work has always dealt with emotions, even though I'm trained as a biologist not to talk explicitly about emotions.

• Jeffrey Brown:

  Whoa, whoa, whoa, why?

• Frans de Waal:

  Well, I was trained by my professors that emotions were taboo as a topic. You could talk about the "motivation" of animals and the "attention to things," but the "emotions" was a sort of taboo topic.

• Jeffrey Brown:

  The change in thinking over the last two decades is reflected in de Waal's new book "Mama's Last Hug".

  Mama was an elderly chimp, nearing death. In 2016, Jan van Hooff, a mentor of de Waals who'd spent years studying and bonding with Mama, came to pay a final visit. Mama locks her old friend in her arms — a rare, physical display of affection between the species.

• Frans de Waal:

  It is almost as if she's calming him down. I think seeing Jan, who was my professor so I know him very well, I think he must have hesitated, because we never go into a cage with a chimp. It's dangerous. It's just not done.

  So to go in there, he must have been a bit nervous. And it's almost as if she has sensed that and she calmed him down, instead of him calming her down.

• Jeffrey Brown:

  What's going on here? De Waal cautions against speaking of Mama's feelings — which he defines as her internal subjective state. But it is possible, he believes, to observe behavior expressing emotions, such as fear, amusement, and empathy.

• Frans de Waal:

  The human studies of empathy started with children, where scientists would ask a family member in the home to cry, and then they would see how very young children respond to them. And very young children who can barely walk, they walk up to this person and touch them and stroke them and try to calm them down.

  And when I heard about that, I said, well, if that is empathy, then I have plenty of empathy in my chimps, because the chimps do this all the time. Someone has lost the fight, has been screaming, sits in a corner. Other chimps come over and embrace them and kiss them and calm them down and groom them.

• Jeffrey Brown:

  In an experiment de Waal often shows audiences, a capuchin monkey is fed cucumbers and seems perfectly happy — until seeing a neighbor getting sweet grapes.

• Frans de Waal:

  People laugh because they — they laugh because they suddenly recognize themselves in the behavior of animals.

• Jeffrey Brown:

  Yes.

• Frans de Waal:

  And they're sort of nervous about that I think.

• Jeffrey Brown:

  Monkey number one now emphatically rejects the lesser treat.

• Frans de Waal:

  Later with chimpanzees, we find even more complicated. In chimpanzees, we find that the one who gets more may also object to it, not just the one who gets less. So we reached the conclusion that the sense of fairness of humans and the sense of fairness of chimpanzees is maybe not that different.

• Jeffrey Brown:

  From his office overlooking the chimps' habitat at Yerkes, de Waal has spent years observing personalities. He knows all the individual ticks of each chimp patterns.

  What happens after a fight? When does one chimp step in to help another? What lures them outside on a rainy day — or causes them to retreat?

  I asked de Waal what we remain unable to know about the inner life of chimps and other animals.

• Frans de Waal:

  One of the most difficult ones is consciousness, and that relates to the issue of feeling.

• Jeffrey Brown:

  Right.

• Frans de Waal:

  So, is it possible that an animal shows all these emotional signs in the face and then in the body and in the behavior without associated feelings, without a conscious sort of being conscious of the emotions?

  I think it's very unlikely. I think that animals like chimpanzees and dolphins and so on, they must have a level of consciousness. But how do we demonstrate that? That is a big puzzle for science.

• Jeffrey Brown:

  Are there inevitable ethical issues, as we learn more about how closely we are related in our emotional life with animals?

• Frans de Waal:

  It has obvious moral implications. I think if you — if animals are machines without feelings and nothing, we can do whatever we want with them. If they're not machines — the point I'm making, and many other scientists are making nowadays, we have to be more careful. We cannot go on treating animals the way we do, if we have this new view of animals. And so, my work is contributing to this change in moral perspective.

• Jeffrey Brown:

  For the PBS NewsHour, I'm Jeffrey Brown at the Yerkes National Primate Research Center.