Humans have long believed that we are somehow special. But many traits once considered uniquely human are shared with animals

Kanzi has good taste. He likes oranges, cherries and grapes.

He points to what he wants on a lexigram, a computerised touchscreen device on which each symbol represents a word. Kanzi can use 500 words and when he is talked to, he can understand a few thousand.

We once viewed ourselves as the only creatures with emotions, morality, and culture

He also likes marshmallows. He will strike matches to light a fire, then warm some on a stick.

Kanzi is not human. He is a kind of ape called a bonobo, which along with chimpanzees are our closest living relatives.

Although he cannot talk like us, Kanzi transformed our ideas about our primate relatives – and in turn, our ideas about ourselves.

We once viewed ourselves as the only creatures with emotions, morality, and culture. But the more we investigate the animal kingdom, the more we discover that is simply not true. Many scientists are now convinced that all these traits, once considered the hallmarks of humanity, are also found in animals.

If they are right, our species is not as unique as we like to think.

Of course not everyone agrees. Read part two, Why humans are unique, to discover the other side of the argument.

A species, by definition, is unique. In that trivial sense humans are unique, just as house mice are unique.

But when we say humans are unique, we mean something more than that. Throughout history humans have created a seemingly impenetrable barrier between us and other animals.

As the philosopher Rene Descartes wrote in the late 1600s: "animals are mere machines but man stands alone".

Charles Darwin was one of the first to speak out against this idea. In The Descent of Man, he wrote: "There is no fundamental difference between man and the higher mammals in their mental faculties" and that all the differences are "of degree, not of kind".

He later extensively documented the similarities between human facial expressions and those of animals.

"If a young chimpanzee be tickled," he noted, "as is the case of our young children a more decided chuckling or laughing sound is uttered". He also observed that chimpanzees' eyes wrinkle, sparkle and grow brighter when they laugh.

His thoughts were later forgotten or ignored. By the 1950s animals had been reduced to unemotional machines with mere instincts.

There was a taboo against attributing emotions to animals

The behaviourist BF Skinner thought all animals were much the same. "Pigeon, rat monkey, which is which, it doesn't matter." He said that the same rules of learning would apply to them all.

At the time, there was a prevailing attitude that they lacked intelligence. There was a taboo against attributing emotions to animals, says Frans de Waal of Emory University in Atlanta, US.

It was only when the primatologist Jane Goodall began her studies on wild chimpanzees in the early 1960s that things started to change, albeit slowly. Her mission was to look at chimpanzees in order to understand more about our ancient human ancestors.

From the beginning of her time in Africa, she saw strikingly human-like behaviours. In her early research she referred to the chimpanzees as "he" and "she" rather than "it". She also gave them names, something previously unheard of in academia, and began to describe their unique personalities.

Tool-use had been considered a uniquely human ability

She also discovered they ate meat: they were not vegetarians as had been assumed. And to get it they were using tools. She saw chimpanzees fishing for termites with twigs.

This in itself was a ground-breaking finding. Until then, tool-use had been considered a uniquely human ability.

Her project leader at the time, the paleoanthropologist Louis Leakey said: "Now we must redefine 'tool', redefine 'man', or accept chimpanzees as humans."

At a similar time, de Waal had been observing chimpanzees in Arnhem Zoo in the Netherlands. He saw many intricate social behaviours, and was frustrated by the lack of studies describing them. "My biology books were useless," he says.

Chimpanzees are extremely good at reading each other's facial expressions

For one, as Darwin had written about over 100 years earlier, de Waal also noted that tickling a young chimpanzee elicits the same smiling response as children. A study published in May 2015 has since shown that the same muscles are involved when chimps and humans smile.

Our incredible range of facial expressions may be unique, but look at the face of a chimpanzee for long enough and you will begin to see a similar complex repertoire of smiling and laughter.

We also know that they are extremely good at reading each other's facial expressions. So are monkeys.

Chimps' social skills are the basis for another behaviour once thought to be uniquely human: morality.

Children have a strong sense of fairness from an early age

Morality can be said to encompass fairness, altruism and empathy. For centuries our moral codes have been crucial to our notion of humanity. We have long believed that our heightened moral reasoning and empathy sets us apart from the beasts.

We know that children have a strong sense of fairness from an early age. For instance, they will share with friends, even if there is an obvious cost to them. They also seem to be innately altruistic: they will help pick up dropped objects without any prompts from as young as 14 months.

But other animals have an innate sense of fairness, too.

In 2003 de Waal published research looking into how capuchin monkeys reacted to an unfair payment.

After two monkeys had completed the same task, both would happily accept a cucumber as a reward. But when one was randomly given a more delicious grape instead, the other was not happy and began to refuse the cucumber.

Chimpanzees behave in a similar way. But what if a chimpanzee controlled the reward instead of a human experimenter?

We know that for the most part, they act selfishly when it comes to food. They are known to steal or hide it from rivals.

However, a 2013 study found that they also know the value of cooperation. They will share food even if there is nothing obviously in it for them. The study found that they will split a reward equally, just as humans do. In one task chimpanzees shared bananas in the same way that humans share money.

Chimpanzees also seem to be instinctively helpful. Just like young infants, chimpanzees will help humans reach for out-of-reach objects.

They also help each other. Chimpanzees will unlock a door that leads to food for a mate, even if the one doing the unlocking would not get any. In the wild researchers have witnessed chimpanzees helping disabled group members, adopting unrelated orphans and helping friends escape from poachers' snares.

Chimpanzees live in a rich social environment

This sense of altruism must run deep in the animal kingdom, because rats will also save a friend from being soaked with water, even if it means getting wet themselves.

These studies suggest that cooperation is a useful survival trait for many species. If humans, chimps and rats all cooperate, the common ancestor of all three may have done so too.

"Chimpanzees live in a rich social environment, they depend on each other," says Felix Warneken of Harvard University in the US. "It does not require a big society with social norms to elicit a deep-rooted sense that we care about others."

The long-held view that chimps are selfish and mean is no longer acceptable, says de Waal. "People say that morality comes from God, from religion," he says, but we can clearly see the roots of morality in many other species.

Chimps can get manipulative

Of course, with the good comes the bad. It would be misleading to only consider chimpanzees as helpful, moral creatures. Just like us, they have a dark side. There are many instances of fighting, murder and even infanticide.

Their society is built upon a complex, hierarchical social world where it is important to keep friends close. That means chimps can get manipulative.

Just watch the clear deception going on in the video below, from the Primate Research Institute at Kyoto University in Japan.

De Waal has called them "Machiavellian", in reference to the deceitful power-grabbing techniques described by historian and philosopher Niccolo Machiavelli.

He saw that a dominant male chimpanzee, who had become powerful with the help of friends, became jealous if these allies associated with his rivals. In response, the male would keep them apart. "As soon as his best buddy starts grooming his rival he gets very upset and breaks it up," says de Waal. "That's a 'divide and rule' strategy."

These insights all suggest that chimpanzees are socially aware and understand each other's behaviour. But how good are they?

Humans can recognise the mental states of others, an ability psychologists call "theory of mind". We can figure out what others are thinking and what their intentions are, and infer what another person does or does not know.

Children learn to do this from a young age, and there is now a lot of evidence that great apes possess many of these mind-reading skills.

For example, a subordinate chimpanzee will only pick up a tasty banana if he can do so without being seen by a more dominant chimp. The subordinate knows that the dominant chimp would claim it.

We are not the only ones who can think about others as individuals with goals

Chimps also have some understanding of human minds. They can tell the difference between a person who is unwilling to give them food and a person who is unable to so.

The latest line of evidence in this field shows that, after food is taken away from them, chimps will steal it back from an opaque box which the experimenter cannot see into. They leave the food in the clear box alone.

Clearly, we are not the only ones who can think about others as individuals with goals, intentions and perceptions, says Katja Karg of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, the lead author of the study.

The next step is to look at whether orang-utans have the same ability, says Karg. We split from them about 14 million years ago, so if they do, it would suggest our mind-reading skills are ancient.

Knowing someone else's mental state also requires a conscious awareness of your own. That suggests that chimpanzees also have a degree of conscious awareness.

They are not the only ones. So far the ability has been found in many other apes, dolphins, Asian elephants and the European magpie.

Chimpanzees even have culture. They aren't composing symphonies but culture can be defined as passing on knowledge, habits and transmission from one generation to the next.

You won't see a chimp cooking a gourmet meal for his best friends but that misses the point. De Waal argues that chimps completely depend on cultural and social learning.

Chimpanzees can learn to cook food, although they do need to be prompted

There is now abundant evidence for this. Wild chimp societies have developed different tool use, courtship and grooming behaviours, which they pass onto their offspring.

In the lab, chimps will conform, using tools in the same way that others do. This conformity is "a hallmark of human culture", according to the researchers. The chimps conformed to their group's social norms, even though another technique could have been just as useful.

Most recently, it has emerged that chimpanzees can learn to cook food, although they do need to be prompted. They would probably quite like a drink to go with it: a 17-year-long study found that they were partial to alcohol from fermented palm sap, and drank enough to show signs of inebriation. Suddenly that gourmet meal idea doesn't look so far off.

Morality, consciousness and culture were all once considered to be uniquely human, but chimps have them all. So what is left?

Language is more than spoken words

Language, clearly. We can write whole books on the topic, chimps do not. We cannot look into their eyes and ask them how they are and expect a verbal response.

Nevertheless, it's clear that they have a complex system of communication.

Chimpanzees lack the vocal structures to make the sounds we do. But language is more than spoken words: gestures and facial expressions also play an important role. When you take that into account, chimps suddenly don't look so bad at language.

Chimpanzees do not have our advanced skills but they have many of the components of language. Kanzi the bonobo, with his language skills, is an extreme case – and he was trained by humans. But there is plenty that chimps can do for themselves.

Chimps have intricate ways of communicating with each other

For instance, one study found that chimps beckon in the same way we do. Other work identified 66 distinct gestures, which all conveyed meaningful information.

They even have cultural variations for the world "apple", which were discovered when a group of Dutch chimps was re-homed to a Scottish zoo.

It is clear that chimps, like many other species, have intricate ways of communicating with each other. The fault has been ours: we have been slow to understand what they are saying.

The more we look for similarities between humans and our relatives, the more we find. "For biologists we are one species out of many," says de Waal.

The differences are not stark and absolute, but rather a matter of degree

He points to the way chimps kiss and embrace after a fight, in order to make up, just as humans do. "If you want to… say it's a very different behaviour, then the burden falls on you to explain what's so different about what the chimpanzees and humans are doing," says de Waal.

There's no doubt that human abilities are more developed than those of chimps, particularly when it comes to spoken language. The point is that the differences are not stark and absolute, but rather a matter of degree – and they get subtler the more we investigate them.

By that measure, humans are no more unique than any other animal.

Not convinced? To discover the other side of the argument, read the companion feature Why humans are unique.