"Thoughts and feelings — the mental processes basically — were off limits," he says. "We were told not to talk about them, because they were considered by many scientists as 'inner states' and you only were allowed to talk about 'outer states.' "
But over the course of his career, de Waal became convinced that primates and other animals express emotions similar to humans. He's now the director of the Living Links Center at the Yerkes National Primate Research Center in Atlanta, Ga., where his office window looks out on a colony of chimps.
"I am now at the point that I think emotions are more like organs," he says. "All my organs are present in a rat's body; and the same way, I think, all my emotions are probably present in the rat."
De Waal writes about primate empathy, rivalry, bonding, sex and murder in his new book, Mama's Last Hug. The title of the book was inspired by a tender interaction between a dying 59-year-old chimp named Mama and de Waal's mentor, Jan van Hooff, who had known Mama for more than 40 years.
"People were surprised [by] how human-like the expression of Mama was and how human-like her gestures were," de Waal says of the interaction. "I thought, 'Well, everyone knows that chimps are our closest relative, so why wouldn't the way they express their emotions be extremely similar to ours?' But people were surprised by that."
On how he became interested in the idea of primate reconciliation
At some point, I saw a big fight in the colony between two individuals. ... And a couple of hours later, I saw a big commotion in the group and two individuals hugging each other, and all the rest of the chimpanzees hooting and yelling and gathering around them. And I did not understand what was going on. I had no clue.
In the evening, I biked back to my home ... thinking about the incident. I thought, "Well, this [is] actually the same two individuals who had the fight." And that's where the word "reconciliation" popped in my mind. ...
And from that moment on, I started looking for it. Each time there was a fight in the colony I said, "Well, what are they going to do afterward?" And I noticed that half the time they come together and they kiss and they embrace and they groom each other. I got really interested in that phenomenon, and I decided to make a study out of that.
On determining that chimps are capable of murder
I was studying the power struggles among the adult males in the colony. [There are] occasional fights, but they're not too bad, usually. But in this case, it completely went out of control, because the males were [in their] night cages and we had tried to separate them the day before. We had done our best to separate them at night because we were worried about the tensions between them. But they didn't want to be separated. They kept clinging to each other. And each time we tried to lower the door, they shuffled in it together. ... We gave up and we decided to let them sleep together. ...
But in that night, one of the males — the leading male — he got basically killed. The next morning, I found him bleeding and near death and he died later in the day. What happened is that the two other males had ganged up on him and they had barely scratches, so they [were] very well-coordinated.
At the time, I must say, I was disturbed, because I thought ,'Maybe this is an effect of captivity and this would normally never have happened.' But now we know [this happens] in the wild as well. So in the wild, chimpanzees ... do kill between groups. [For] some males who are strangers to each other, that's a fairly common occurrence.
On the spectrum of primate behavior
Just like humans have that whole scale of possibilities — from positive to negative — we find the same thing in the chimpanzee. ... When people say, "Well, you may say that they have empathy, but they actually kill each other!" But you know, the same argument we could use for humans. No one would say that humans have no empathy or altruism just because we also, on occasion, kill each other. We know that that's a spectrum of behavior that we have, and the same thing is true for many other species. They can go all the way from killing each other to loving each other.
On the role of the alpha male in chimpanzee colonies
"Alpha male" in my field just means the top male. You have the top male and the top female. You have only one of them. You cannot have two alpha males in a group of chimps, or two alpha females. It means the top individual, and the term comes out of wolf research. ...
The alpha male has many duties. ... A good alpha male breaks up fights and defends the underdog — not the winners, usually, but the losers. And the alpha male also is the consoler-in-chief, [who] goes to individuals after a fight to console the ones who have lost and sit with them and groom with them and hold them and things like that. And so the consoler-in-chief role is extremely important and an alpha male who is good at that, he is also usually kept in power for longer.
In a chimpanzee society, [there are] always ... challengers to the top male. And it's almost as if the group is waiting [to see] if the male is a bully, [or if] they don't like him. ... If it's a good alpha male who keeps order and is protective and is not abusive, then they try to keep that male in power.
On alpha females in bonobo colonies
I don't know a single colony of bonobos in captivity that is not led by a female. In the wild, we now know that most of the time, also at the top of the hierarchy, it's females more than males. Bonobos are a very female-dominated society.
If you ask, 'How do these females get to the top?' That's an interesting problem. ... Age and personality are the main factors. There's actually very little open competition and politics going on, [in contrast to] the way it is among the males. If you wait long enough, you get old enough and you have a strong personality, you can be the alpha.
In both bonobos and chimps I very rarely see a middle-aged female dominating these older females. If you have a group [of] a few 25-year-old females and a few 40-year-old females, and the 40-year-olds really are physically not as strong as the 25-year-olds, I can tell you ... it's going to be the 40-year-old females who were at the top. That's a very different situation from the males. In the males if you get too old, you get weaker and you're going to be kicked out of the top position.
On how Capuchin monkeys experience unfairness
If you give both monkeys pieces of cucumber they're perfectly fine and they will [take it and eat it] 25 times in a row without any problems. If you give both of them grapes — and grapes are 10 times better than cucumber — they also perform 25 times without problems. The trouble starts when you feed one monkey grapes and the other one cucumber. The one who is shortchanged (because cucumber is not as good) then starts to refuse and actually becomes agitated and may throw the cucumber out, or may at least stop performing and sit in the corner and not [do] the test anymore — which is very strange because the food is normally good. And any [other] time you give a piece of cucumber to one of these monkeys they will eat it, but under these circumstances they don't. So they get sort of pissed off at the whole situation. ... It's an inequity of response. It has to do with fairness.
On what he calls "anthropodenialism"
I think anthropomorphism is not such a big deal with species that are close to us, and that's why I invented the word anthropodenial, which is the opposite. [It means] that you deny that there are connections between humans and other species. And actually, entire areas in the university — like philosophy, anthropology [and] parts of psychology — they are anthropodenial. ... They're saying that the human mind and the human spirit are so totally different, we cannot compare them with what a monkey or a dolphin or [another] animal is doing. They are denying that connection, which I think is detrimental and is actually much more dangerous, in my opinion, because anthropodenial has a lot of negative side effects in my mind. It's much more dangerous than anthropomorphism.
Roberta Shorrock and Mooj Zadie produced and edited the audio of this interview. Bridget Bentz and Molly Seavy-Nesper adapted it for Shots.