We all know the story: give every chimpanzee on the planet a typewriter and wait until something monumental occurs, either the recreation of the complete works of William Shakespeare or the heat death of the universe. Last year, mathematicians concluded the chimps would never achieve the former – the likelihood of one typing even the more modest “bananas” in its lifetime is a meagre 5 per cent. That some of our closest relatives fail this test speaks to how human culture is like nothing else in nature. Ask biologists to explain why this is, however, and things get complicated.
The problem became clear this century as studies revealed that culture, far from being uniquely human, is present across the animal kingdom, from whales to ants. This has encouraged researchers to search for the key ingredient that explains why our culture – and ours alone – flourished.
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It hasn’t been easy, and for a surprising reason: animal cultures are far more sophisticated than we assumed. We once thought they couldn’t become more technologically advanced, yet research published a few months ago suggests they can. We also suspected that animals lacked the smarts to learn complicated behaviours from one another – but last year, we discovered that even bees may be sufficiently brainy to do so. “Views have changed,” says , an animal cognition researcher at Utrecht University in the Netherlands. “We now know much more about animals than we did before.”
In updating our expectations of animal cultural behaviour, though, we seem to have made explaining the culture gap much harder. So, how do we understand the divide?
For decades, few researchers were prepared to accept that any non-human animal had culture. Indeed, it was Eurocentric culture that denied animals theirs. Going back at least as far as Plato, 2300 years ago, Europe’s great thinkers imagined the existence of a chain of being with humans distinctly above all other animals, says , a cognitive scientist at the University of Sheffield, UK. Elsewhere in the world, “things tend to be viewed as a lot more interconnected”, she says.
What is culture?
Perhaps it is unsurprising, then, that one of the first people to suggest that animals might have cultural traditions roughly akin to our own was Japanese biologist Kinji Imanishi. He began advocating for animal culture in the early 1950s as part of a broader argument that some animals have human-like characteristics – and faced ridicule from some European and North American researchers for doing so, says Bridges. But evidence continued to mount – including the discovery in the 1960s of . It was in the 21st century, however, that research into animal culture exploded.
This may baffle many members of the general public, at least in the West, who might struggle with the idea of animal culture. But this is largely because in Western countries, people typically associate culture – a fuzzy term, with multiple definitions – with artistic and intellectual activities. Biologists have come to adopt a less human-centric definition. “Culture is shared,” says van Leeuwen. This means that any behaviour – whether that be using sticks to dig for termites or learning to play the piano – becomes cultural through the act of spreading to other community members. Use this definition and animal culture turns out to be common. Nevertheless, no animal cultures rival the complexity of our own, and biologists became eager to know why.
In the early 2000s, many began to favour one interpretation in particular. It is clear that our cultural behaviours and tools change as they spread to new populations and pass down the generations, often becoming more sophisticated in the process. The argument went that other animal cultures don’t do this, meaning we alone have what biologists have dubbed “cumulative culture”.
A few years later, , a behavioural biologist now at the University of Tübingen, Germany, and his colleagues suggested an idea to help explain the lack of cumulative culture – in chimpanzees, at least. Chimps, they argued, don’t have this because they aren’t very good at learning how to master a new skill from each other. Tennie acknowledges that this idea sounds counterintuitive, not least because it clashes with what popular culture has to say about chimps. “We often talk about aping someone’s behaviour,” he says. As such, it’s easy to think we know what is happening when an unusual skill – using stone tools to crack nuts, for example – spreads through a chimp population, he says: one chimp innovated the behaviour; the others picked it up through imitative copying.
Why apes can’t ape
But Tennie and his colleagues argued that this can’t be what is really happening, because their experiments suggested that chimps are poor imitators. Tennie says this means each chimp must develop its skill set independently. Under this scenario, the first chimp discovers how to crack nuts using stones. A second chimp is intrigued, but, being unable to ape the behaviour, it instead chooses to examine the nut-cracking site once the first chimp has moved on. Guided by the presence of stones and uncracked nuts, this second chimp begins experimenting and eventually works out for itself how to crack nuts. “It’s a process of reinventing the wheel,” says Tennie.
Crucially, says Tennie, this imposes a limit on cultural development. Many of our cultural tools have accrued so many changes over the generations that they are now too elaborate for a novice to reinvent from scratch. It is highly unlikely, for instance, that an untrained individual could build a violin after simply examining a Stradivarius: what is needed is guidance from an expert instrument-maker. If chimpanzees can’t rely on that guidance because they don’t imitate one another, their culture is restricted to innovations that any individual chimp could invent for itself – innovations that lie within what Tennie calls the zone of latent solutions (ZLS).
The difference may be in the way human culture continues developing
Over the past decade, Tennie and his colleagues have collected additional evidence that they argue favours . But the idea who insist that chimps and some other animals, including pigeons, learn through imitative copying and do have cumulative culture. A particularly clear example was published last year by a team that included , an evolutionary ecologist at the University of Zurich in Switzerland and , an evolutionary psychologist at the University of St Andrews, UK. The researchers knew that chimps in some wild populations have complex toolkits – for instance, they may use stout sticks to poke holes in termite nests, then insert thinner sticks to fish for the insects.
Using genetic data, the team discovered that different chimp populations with such toolkits are particularly likely to have been in contact with one another within the past 15,000 years. What’s more, these links – and the links with populations that use simpler tools – suggest the toolkits have spread from population to population, becoming more technologically advanced as they did so. “However, since chimpanzee migration rates are limited, this also implies that the spread and accumulation of these tools is limited,” says Gunasekaram.
Monkey see, monkey do
Strictly speaking, this result doesn’t directly challenge the ZLS hypothesis. Chimp cultural tools could become a little more advanced while remaining simple enough for each individual to reinvent them. But a few months before Whiten and his colleagues published their findings, two studies undermined the idea that this limitation exists. Both concluded that animals can indeed learn elaborate skills that they couldn’t invent for themselves by watching another animal performing them, in much the same way that a novice can learn to make violins by watching a professional instrument-maker.
The studies – one in chimpanzees and one in bumblebees – were far from easy to conduct. By necessity, they both involved presenting the animals with a puzzle that was too tricky for any individual to solve on its own. Then came the difficult part: isolating individual animals and teaching them how to solve the puzzle.
In the case of the bees, this meant teaching one of the insects that it couldn’t access a food reward visible behind a clear plastic sheet by making a beeline straight towards it. Instead, the bee had to take a detour and push a lever that would then allow it to move the plastic and reach the reward. “That wasn’t at all trivial to the bee,” says Bridges, who led the study. It was only by bribing the insect with a smaller reward near the lever that the researchers could encourage it to make the detour. They then had to wean the bee off the bribe until it would make the detour simply to gain access to the original, large reward. The whole training process took two days. The final stage of the experiment involved having the trained bee solve the puzzle in the presence of an untrained bee. Remarkably, within 10 hours, some untrained bees began following in the footsteps of the trained bee and learned to . “When we saw the bee learn the solution from the demonstrator, we all went wild,” says Bridges.
It was the same story with the chimps. This study, led by van Leeuwen, involved placing what was in effect a peanut vending machine in a large, forested enclosure at the Chimfunshi Wildlife Orphanage Trust in Zambia, which is home to dozens of chimpanzees. Over the course of three months, none of the chimps worked out that they could dispense peanuts by opening a drawer on the machine, inserting a wooden ball and then closing the drawer again. But once van Leeuwen and his colleagues taught a couple of them how to operate the machine, the skill quickly .
Tennie isn’t convinced that the experiments are a fatal blow to the ZLS hypothesis. He suspects, for instance, that the chimps could have worked out how to operate the vending machine eventually. He says they may have failed to do so in the three months they were given because the enclosures at Chimfunshi are many hectares in size, offering distractions that can fill the chimps’ days. But others say the studies are valuable. “I think they push the boundaries back on our understanding of whether animals can learn things that go well beyond what they could individually work out,” says Whiten. If that view is correct, the studies imply that other animal cultures may be more complex than we had thought – even in creatures like bumblebees, whose brains are about the size of a sesame seed. They also suggest we are further than ever from explaining why human culture is so clearly different from any other on Earth.
There are, however, possible ways forward. One might be to recognise that there is a difference between demonstrating that animals can learn difficult skills from each other and showing that they do this regularly enough to influence their cultural development.
For instance, although Whiten thinks chimps can copy one another, he thinks that, compared with humans, they are much less motivated to do so. He speculates that this might reflect their broader evolutionary history. Our ancestors left the forests and began exploring new environments and exploiting new foods, particularly nutrient-rich meat, so natural selection may have favoured hominins who were willing to learn useful skills from one another. Chimps’ ancestors stayed in the forests, maintaining their traditional way of life, so natural selection might have favoured individuals with a more conservative outlook. “Despite their intelligence and their ability to learn from others, chimpanzees are just not that willing to try something new,” says Whiten.
Human culture’s endless creativity
For , an evolutionary anthropologist at Arizona State University, meanwhile, the difference may be in the way human culture continues developing almost indefinitely, going from stone tools to metal axes to industrial log-splitting machines. “Humans can and do push all that way, but basically all other species seem to run up against some sort of constraint,” he says.
Last year, Morgan and , a biologist at Stanford University in California, argued that brains – and the way individuals mentally represent actions and goals – . For instance, if a human wants to produce a small stone figurine, they must hold that idea in their working memory while they scout for carving tools and then turn an unshaped stone into the artwork in their mind’s eye. The evolution of larger brains – perhaps fuelled by our ancestors’ taste for highly nutritious meat – might have given us the working memory capacity to dream up and carry out such complex tasks. Animals with smaller brains and more limited working memory capacity may struggle to do so. “I think it’s totally plausible that if you have more working memory then that gives you a bigger canvas to see the bigger picture,” says Morgan.
Put the pieces together and this suggests that several factors helped widen the culture gap. Genetics may have played a part in encouraging our ancestors to value innovation over conservatism. Behaviour may have played a part in allowing us to exploit new foods that fuelled brain growth. And larger brains may have played a part by allowing us to store more information, think up new ideas and retain our focus on those ideas. “There is no single silver-bullet explanation,” says Whiten.
Tennie broadly accepts this conclusion. “When we first outlined the ZLS hypothesis, my colleagues and I stated that several things had to come together for human-like culture: cooperation, teaching and so on,” he says. But he adds that researchers know there is more to do than simply declare that the picture is complex. The challenge now facing biologists is to devise clever experiments that assess exactly which factors played a key role in catalysing our cultural development, and which were of lesser importance. After all, science has a culture too, and experiments are one of its core features. We may need many more of them to fully solve the mystery of the culture gap.
