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What makes a human?

Sep 23,2017 - Last updated at Sep 23,2017

Last month, moviegoers flocked to theatres to see “War for the Planet of the Apes”, in which an army of retrovirus-modified primates wage war against humanity.

Chimpanzees on horseback, machinegun-wielding gorillas and scholarly orangutans undoubtedly make for good theatre. But could anything like this ever happen in real life?

In “Planet of the Apes”, Pierre Boulle’s 1963 novel upon which the films are based, space traveller Ulysse Mérou is stranded on a terrifying planet ruled by gorillas, orangutans and chimpanzees who have copied their former human masters’ language, culture and technology.

The humans, meanwhile, have degenerated into brutal and unsophisticated beasts.

Much of the sinister realism in “Planet of the Apes” stems from Boulle’s impressive attention to scientific detail and knowledge of research into animal behaviour at that time. 

His book tapped into the still-popular notion that animals such as chimpanzees and dolphins have complex but covert communication systems that humans cannot even fathom.

Many people would prefer to think that all those “arrogant” scientists who have concluded that animals cannot talk have simply failed to decode animals’ calls.

But Boulle’s book is decidedly a work of fiction, because apes here on Earth could never actually acquire human culture solely through imitation.

In reality, complex culture requires underlying biological capabilities that are fashioned over long periods of evolution. Chimpanzees simply do not have the vocal control or physiology to produce speech.

Moreover, modern apes could not be made highly intelligent even with brain-enhancing drugs. And although microbes can change behaviour — such as when rabies renders its host violent and aggressive — they could never bestow language upon a species.

We know this because animal communication has been investigated extensively for more than a century, and the scientific evidence yields few hints of truly complex communication faculties in non-human species.

For example, in the 1940s, researchers raised a chimpanzee named Viki in their home. But Viki learned just four words — “mama”, “papa”, “cup” and “up” — which was more than could be said for an earlier experiment in which a chimpanzee and a human child were reared together.

That exercise had to be abandoned after the chimpanzee failed to learn a single word, and the child actually started imitating chimpanzee sounds.

In the following decades, studies teaching apes sign language generated much excitement. And yet, virtually all linguists would agree that the apes in these experiments had not produced language.

They could memorise the meanings of signs, but they could not learn the rules of grammar.

Tellingly, utterances by “talking” apes proved to be exceedingly egocentric.

When equipped with the means to talk, apes’ communications are limited to expressions of desire such as “Gimme food”.

The longest recorded statement of any “talking” ape, by a chimpanzee named Nim Chimpsky, was: “Give orange me give eat orange me eat orange give me eat orange give me you”.

It turns out that chimpanzees, bonobos and gorillas make for poor conversationalists.

By contrast, within months of uttering their first words, two-year-old children can produce complex, grammatically correct and topically diverse sentences comprising verbs, nouns, prepositions and determiners.

They can do so because human minds have evolved to comprehend and produce language.

Many scholars believe that language emerged from the use of meaningful signs.

Our ancestors were immersed in a symbol-rich world, and this generated evolutionary feedback favouring the neural structures that enable us to manipulate symbols efficiently.

The syntax in human language today was made possible by our ancestors’ long use of symbolic proto-languages. Genes and culture coevolved to reorganise the human brain.

The same is true of warfare, which is much more than just scaled-up aggression. In war, complex institutions dictate strict behavioural codes and individual roles that facilitate cooperation.

Research suggests that this level of cooperation could not evolve in a species that lacked a complex culture, and such features as institutionalised punishment and socially sanctioned retaliation.

Most of these norms are not obvious, and thus have to be inculcated, usually during youth.

But even among apes that are proficient imitators, there is little compelling evidence that behaviours are actively taught. When apes do cooperate, it is largely to help relatives.

The scale of human cooperation, which involves huge numbers of unrelated individuals working together, is unprecedented largely because it is built upon learned and socially transmitted norms.

There is now extensive evidence that our ancestors’ cultural activities changed the human brain through natural selection, which then further enhanced our cultural capabilities in recurring cycles.

For instance, milk drinking began with early Neolithic humans, who were consequently exposed to strong selection favouring genes that break down energy-rich lactose.

This genetic-cultural co-evolution explains why many of us with pastoralist ancestors are lactose tolerant.

It is little wonder that Boulle put such an emphasis on imitation.

Humans are descended from a long line of imitators, who mimicked each other’s fear responses to identify predators and avoid danger.

Today, this is reflected in empathy and other forms of emotional contagion that make movies a heartfelt experience. Without these traits, we would all watch movies like sociopaths, equally unmoved by a murder or a kiss.

It was also through imitation that our forebears learned how to butcher carcasses, build fires, and make digging tools, spears and fishing hooks.

These and countless other skills left us supremely adapted to decipher others’ movements and reproduce them with our own muscles, tendons and joints.

Eons later, today’s movie stars demonstrate the same aptitude when imitating the movements of other primates, with a precision that no other species can match.

Human culture, having evolved over millennia, is not something that another species can easily pick up.

We can rest assured that there will be no inter-primate war on Earth. For that to happen, another species would have to undergo a similarly prolonged evolutionary journey.

And the only real warmongering ape on the planet seems hell-bent on preventing that.



The writer is professor of behavioural and evolutionary biology at the University of St Andrews, the UK, and author of “Darwin’s Unfinished Symphony: How Culture Made the Human Mind”. ©Project Syndicate, 2017.

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