In The Field

AAAS: Goodbye from “cucumber land”

With the meeting wrapping up today, the celebrated researcher Frans de Waal brought Darwin’s legacy into the modern world at a symposium on the evolution of morality.

Human morality has perplexed scientists and thinkers since Darwin’s time, but De Waal argued that it was not perplexing to Darwin himself, because he saw morality as linked to emotion, and saw reflections of human emotion all around us in other animals. De Waal, of the Yerkes National Primate Center at Emory University in Atlanta, described today the years of evidence that he and other scientists have gathered to support the idea that other animals show emotional and moral behaviors much like those in the human species.

For instance, chimpanzees shown videos of other chimps yawning yawn themselves, exhibiting a phenomenon called “motor contagion.” And mice show “emotional contagion,” responding to pain applied to other mice. Both these mechanisms are ways in which one animal can share the experience of another, which is an essential part of empathy, De Waal said.

Monkeys also show “prosocial behavior” in a task in which they are asked to choose either a block that will elicit a treat for themselves and a partner monkey, or a block that will only elicit a treat for themselves, De Waal said. The monkeys in this experiment more often choose to distribute treats to both themselves and the partner monkey, especially if the partner is related to them, De Waal said: “Monkeys do care about someone else,” he argued.

And finally, De Waal said, monkeys also reject unfair treatment – and here’s where he brought the whole argument back to the human world. His group trained pairs of monkeys to perform a simple task and get a piece of food – either a cucumber or a far tastier grape – as a reward. If both monkeys in the pair are rewarded with cucumbers, they happily perform the task eagerly and often. Yet if one monkey suddenly starts receiving grape rewards, while the other is stuck with cucumbers, the cucumber recipient tosses the inferior food out of his cage. And eventually, he goes to the corner of his cage and refuses to perform the task any more.

To De Waal, this signifies that monkeys, like humans, have a strong sense of fairness – a finding that has been reinforced in other animals, such as dogs. So, De Waal argued, it makes perfect sense in the light of evolution that we become outraged when we hear that Wall Street bankers are receiving extravagant bonuses while the rest of us are struggling to fill our gas tanks and pay our mortgages. “I always think we live in cucumber land and they live in grape land,” De Waal said.

And with that, the meeting ends this afternoon. My brain is overstuffed and I could use a good night’s sleep, but it’s been a fascinating and thought-provoking few days in cucumber land.


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