The Big Question: What does forward-planning reveal about chimps' relationship to humans?

Why are we asking this now?

A chimp called Santino in Furuvik Zoo in Sweden has been found to be capable of planning for the future by calmly building up a cache of stones in the early morning hours ready for opening time when he would then hurl them at gawping visitors. According to scientist Mathias Osvath of Lund University, Santino's behaviour shows that our fellow apes consider the future in a very complex way.

"It implies that they have a highly developed consciousness, including life-like mental simulations of potential events," Dr Osvath said. "They most probably have an 'inner world' like we have when reviewing past episodes of our lives or thinking of days to come. When wild chimps collect stones or go out to war, they probably plan this in advance. I would guess they plan much of their everyday behaviour." This is not the behaviour we come to expect of "dumb" animals – chimpanzees appear to be almost human-like.

In what other ways do chimps show similarities to humans?

There are several different observations that point to their human-like nature. Chimps who have undergone medical experiments, for instance, exhibit the classic behavioural symptoms shown by people who have suffered extensive torture. The hand gestures of chimps – such as the open-palm begging posture – are similar to those of humans and might derive from a common origin.

Wild chimps have also been found to engage in a form of primitive warfare against neighbouring chimps. They also experience infectious yawning, when one yawning member of a group sets off yawning in everyone else. Chimps are also prone to many of the viral infections of humans, such as Ebola and HIV. All in all, they are really quite human in many respects.

Any specific examples of behaviour in common?

Several. A female chimp called Ai, for instance, was taught to count to 10 and to remember five-figure numbers, just two short of the seven-digit telephone numbers most people can just about recall.

Another chimp called Panbanisha had been trained to understand simple English sentences, although this fell short of being able to communicate in a true, spoken language. The chimp was brought up to remember a lexigram, a computer screen full of symbols which she can press to produce a rudimentary response to a human voice.

Panbanisha became able to recognise certain favourite or key words, such as "outdoors" and "M&Ms", when spoken in the proper context with a certain intonation. Another chimp, called Kanzi, would accurately locate the correct printed symbol on a lexigram for a given spoken word or phrase. This suggests that they can identify spoken sounds, even if the understanding is limited in the context of speech and language.

But are these just tricks or do they suggest a higher intelligence?

Of course animals kept domestically can be trained to perform a wide variety of seemingly clever tricks, although there is mounting evidence that wild chimps have a more sophisticated understanding of the world than scientists once gave them credit for.

Take, for instance, the use of tools, which was once considered to be a defining feature of humanity. Wild chimps are now known to use tools widely, such as the use of sticks to "fish" for termites or stones to crack open hard nuts. Indeed, a few years ago scientists filmed chimps using a "tool kit" to fish for termites. They would create a hole in a termite nest with one, thick stick and push another, thinner stick with a deliberately frayed end down the same hole to catch the termites. This was the first known example of chimps using two different tools to perform a given task.

Humans have culture. What do chimps have?

If culture is defined as passing on learning and tradition to future generations, then chimps have it. Ten years ago, scientists published a large study drawing on a knowledge of more than 150 years of chimpanzee observations in the forests of central Africa showing that wild chimps have an array of traditions that they pass on to their offspring.

The scientist showed that while there were several examples of chimp behaviour, such as drumming on trees, that were shared across the entire region, there were many other examples – about 40 in total – that had evolved separately in different areas of the region and passed on to subsequent generations inhabiting that area.

The chimps in Gombe national park in Tanzania, for instance, would fish for ants using a long branch which they would regularly swipe with their hands to collect the insects into a ball that they would put into their mouths.

The chimps at other sites, meanwhile, would fish with shorter twigs that they would lick with their lips and tongues – a far more inefficient method. Scientists said that the difference came down to cultural practice passed on down the generations of geographically separated troupes of chimps.

How closely related are chimps to humans?

We are so close in terms of our genes that the science writer Jared Diamond once famously called us the "third chimpanzee" – the two others being the common chimp and the pygmy chimp, or bonobo. A genetic comparison suggests we share about 98 per cent of our DNA – give or take a few per cent depending on what is being compared. We share a common ancestor that lived between 5 million and 7 million years ago. One study has calculated that the split between humans and chimps occurred 6.3 million years ago, although there may well have been many centuries or millennia of continued cross-breeding between ancestral chimps and ancestral humans.

Should we think of chimps as a variation on humans?

They are so close that some scientists have indeed suggested that they should be included in the human lineage on the grounds that they are closer to us than to the other great apes, such as gorillas. Leaving aside the details of our common evolutionary heritage, it is clear that chimps are the closest living relative of humans.

So what makes chimps different to humans?

Brain size is probably the most important physical features. The human brain is about three times larger than the brain of chimps for our body size. It is this immense growth of the human brain during the few millions years of evolutionary history that really distinguishes the two species and determines the uniquely human traits such as language, consciousness and creativity.

We also walk on two legs, whereas chimps have gone down the less-efficient knuckle-walking path. Bipedalism has freed our hands for using tools and to move large distances over open savannah, rather then being confined to forested areas. Tools and the control of fire has enabled humans to exploit a different, more nutritious diet than chimps. The other thing that separates male chimps out from men is the relative size of their testicles – the much bigger testes of chimps indicates that they are more promiscuous by nature than humans.

So should chimps be classified as humans?

Yes...

* We share 98 per of our DNA with chimps as well as a relatively recent common ancestor

* Chimps are more closely related to humans than they are to other apes such as gorillas and orangutans

* They have a form of higher intelligence and awareness that is on a par with human children

No...

* They are a distinct species of animal separated by millions of years of evolution

* Classifying chimps as humans would denigrate the definition of what it is to be human

* We would find ourselves on a slippery slope to other forms of detrimental anthropomorphism

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