What makes humans unique? “To think about thoughts and then reflect on them”

Foto: Jeroen Oerlemans

“Together with colleagues, I sifted through millions of publications – from anthropological field reports and philosophical treatises to the latest biological findings. We also combed newspapers in as many languages as we could. Our question: what has been written about the relationship between humans and animals?”

In your book you mention Aristotle (born 384 BC), who put humans above animals. That idea stuck for centuries. What discoveries challenged it?
“People usually say it was Darwin who placed humans among the animals in the tree of life. But that still didn’t prove that many of our cultural traits can also be found in animals. The real shift came in 1948, when Japanese primatologists led by Kinji Imanishi observed a troop of macaques. One female macaque started washing her sweet potato before eating it. Other macaques then imitated this behaviour, since eating a washed potato meant no sand between your teeth. Offspring adopted the behaviour too. That was the first evidence that animals also have a history.”

“At first, people scoffed. But soon after, Jane Goodall discovered that apes also have mourning rituals and ceremonial behaviour that differ from group to group. Some chimpanzees dance wildly at waterfalls or in the rain. Culture was also spotted in otters, crows, fish and bees. Different bee colonies, for instance, have their own dances to show where honey can be found, sometimes kilometres away.”

“For ages we said: only humans can think ethically. But we now know that many animals – dogs and chimpanzees among them – do have a sense of right and wrong. Language was long thought to be uniquely human, yet dolphins and many other animals clearly communicate. We haven’t cracked dolphin language yet, but what we can see is that they take turns speaking, waiting until the other has finished. They even give each other names with signature whistles.”

“For ages we said: only humans can think ethically. But we now know that many animals – dogs and chimpanzees among them – do have a sense of right and wrong. Language was long thought to be uniquely human, yet dolphins and many other animals clearly communicate. We haven’t cracked dolphin language yet, but what we can see is that they take turns speaking, waiting until the other has finished. They even give each other names with signature whistles.”

“Of course, we’re studying behaviour – we can’t know what’s really going on inside an animal’s mind. But we can identify patterns, and draw analogies. Some animals even ‘marry’. The Adélie penguin offers its mate a black pebble; if accepted, they stay together for life. It’s hard not to feel humbled when you see that.”

“Our aim was to bring together all the claims about human uniqueness, alongside research on similarities between humans and animals. No one had done that before. Then we looked for deeper patterns.”

And what patterns did you find?
“What we saw in all forms of life was a pattern of recursion. The word comes from the Latin recurrere, meaning ‘to return’. You see it in thinking about thoughts, in making tools for producing other tools, in the use of subordinate clauses in language, or in the search for patterns within patterns in order to find yet more patterns.”

“Some animals can think, and sometimes even reflect on what they know or don’t know. But what we’ve never observed in animals is thoughts about thoughts – and then reflecting again on those.”

“Humans can. That endless search for patterns within patterns, what I call unbounded recursion, seems unique to us.”

So humans are unique after all?
“Yes – just as every animal is unique. That doesn’t make us ‘better’. Take echolocation: bats are far superior. But unbounded recursion gave us cumulative culture. That’s given us great things – art, science, progress. But also destructive culture – nuclear weapons, for instance.

“When chimpanzees get angry, their grudges are quickly broken and reconciliation follows. Humans are far less forgiving. In Sardinia, for centuries there was a system called la faida – a culture of blood feuds. Families nursed grudges for two thousand years, killing each other’s members generation after generation. That capacity for multi-generational vendettas is uniquely human. You see the same dynamic in modern conflicts – Gaza, for instance – where revenge and memories of injustice keep getting passed down.”

And where does that characteristic ultimately lead?

“That is difficult to say. If you can be aware of the recursive capacity we possess, then hopefully you can also decide: let us restrain it, and not escalate.”

You previously wrote a history of knowledge, of the humanities and of meaning. Where does your fascination with overview studies come from?

“I myself grew up without books, in a very small village in the Achterhoek, Beek. Until I was twelve there was not a single book in the house, as my parents were Catholic not even a Bible. The first book I ever held was a dictionary, which I got for Saint Nicholas (Sinterklaas in Dutch). I found it fantastic! It gave me an overview, I still have it. Perhaps my urge to write survey works stems from that.”