ALAN ALDA (NARRATION) At least a glimpse of what’s going on in the heads of our primate relatives has recently come not from our cousins the chimpanzees but from what might be thought of as second cousins twice removed ¬– rhesus monkeys. Humans and monkeys last shared a common ancestor some 14 million years ago, so there’s much more evolutionary distance between us and them than the 6 million years that separates us from chimps.

LAURIE SANTOS I like to be so that the monkey has to walk that way…

ALAN ALDA (NARRATION) But Yale University psychologist Laurie Santos sees in that distance a valuable perspective.

LAURIE SANTOS The reason I got into this is not because I’m interested in monkeys or what they know about the world. I just think that the monkeys are a really clean way to study the evolution of our human nature. So in fact, I’m not in it for the monkeys. I’m in it for the humans.

ALAN ALDA (NARRATION) Laurie and her students come frequently to this small Caribbean island. For some 70 years it’s been home to a lively population of rhesus monkeys maintained solely so that researchers can study their behavior in a natural setting.

Today, the plan is to demonstrate for us an experiment that has done much to convince even skeptics that monkeys have at least a working notion of other minds.

RESEARCHER Monkey! Monkey! Monkey, look!

ALAN ALDA (NARRATION) A monkey is tempted by two grapes. Both are placed on the ground – but only one human turns her back.

Almost every time Laurie Santos and her students have done this test, the result is the same: the monkey steals the grape from the person who isn’t looking.

The idea for the experiment came as much from the monkeys as from the researchers.

LAURIE SANTOS The embarrassing thing is it was a first hand experience of getting ripped off by a monkey. We’d had many of these unfortunate experiences of running these other studies that had food and so on, and we’d put a lemon to the side, write something in our notebook, and look back, and the lemon was running up a hill, being carried by a monkey. So we said, well, you know this is behavior they seem to do naturally. They seem to understand something. But what do they really understand about it. So that was how we got into using this behavior to really look at what they know about our perceptions and hopefully our mental states.

ALAN ALDA (NARRATION) Watch this monkey as he steals the grape from the person with her back turned. There’s no doubt the monkey is checking if he’s being watched. But does this mean he understands that he’s dealing with thinking beings?

LAURIE SANTOS We’re finding that the monkeys are very good about thinking about where eyes are pointed, and so on, but only in this really restricted context, so only in the context of stealing food from us. So one of the remarkable differences, and the things that the human species seems to be really good at, is actually applying these strategies more broadly.

ALAN ALDA (NARRATION) So Laurie’s research with monkeys suggests they have a glimmer of awareness of other’s minds. And Frans de Waal’s take on chimpanzee politics argues that the sort of social scheming they do suggests that, at least at the level of basic emotions, chimps too can see into each others’ minds. But beyond that…

BRIAN HARE The question is, can they say, OK, I’m thinking about his thoughts, I’m thinking about...what does he think about me? And then I’m also projecting into the future and I’m thinking what is it that I want? And also I’m thinking about what is it that I’m feeling, and what will I be feeling? And what should I do now? So that’s really complicated and putting all that stuff together, I think, is what it is to be human.

ALAN ALDA So this sounds like the birth of politics…He really scared me that time! He’s being political right now! However, when we started to get political in the way we are, we didn’t just make these displays constantly, we started to say, we had the ability to say, “I can work on you and get you to see it my way and I can persuade you, or I can make you think a different way. And I’m keeping track of how you’re thinking, and I know what you’re thinking of me, and in effect, I can sell you this car.”

BRIAN HARE Bingo... it was the birth of the car salesman.

ALAN ALDA (NARRATION) So a major difference between us and chimpanzees seems to be in our much greater ability to read – and even manipulate – each others’ minds: a social skill.

To explore this idea that the Human Spark – the key difference between us and our non-human primate relatives – lies in our greater social skills, I’ve come to Leipzig, Germany, where the zoo houses one of the world’s largest collections of apes.

Here there are gorillas, who went their separate evolutionary way some 12 million years ago.

Bonobos, close relatives of chimpanzees.

Chimpanzees, of course, with 6 million years of independent evolution.

And orangutans, our most distant ape cousins, who unlike the African apes forged their own path in Asia starting some 15 million years ago.

I’m here with Mike Tomasello, who’s spent his whole career comparing the abilities of apes and humans.

ALAN ALDA Hello pal, hi. Oh, sorry. What did he think?

MICHAEL TOMASELLO That was a greeting.

ALAN ALDA Oh that was? You know they’re so big and hairy they really scare me a little, these guys.

MICHAEL TOMASELLO No, he’s a gentle giant.

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