What makes human

We evolved from earlier creatures, each on a unique trajectory through time. We share DNA with all the organisms that have ever existed; the proteins our genes encrypt utilise a code that is indistinguishable from that in an amoeba or a zebu.

How did we become the beings that we are today? Precisely when these facets of our lives today arose in our species is debated. But we do know that within the last 40, years, they were all in place, all over the world. Which facet singles us out, among other animals — which is distinctively human? Navigating this territory can be treacherous, and riven with contradictions. We know we are animals, evolved via the same mechanisms as all life.

This is comprehensively displayed in the limitless evidence of shared evolutionary histories — the fact that all living things are encoded by DNA. Or that similar genes have similar functions in distantly related creatures the gene that defines an eye is virtually the same in all organisms that have any form of vision. Prudent scepticism is required when we compare ourselves with other beasts. Evolution accounts for all life but not all traits are adaptations. We use animals in science every day to try to understand complex biochemical pathways in order that we might develop drugs or understand disease.

Mice, rats, monkeys, even cats, newts and armadillos, provide invaluable insights into our own biochemistry, but even so, all researchers acknowledge the limitations of those molecular analogies; we shared ancestors with those beasts millions of years ago, and our evolutionary trajectories have nudged that biochemistry to suit each species as it is today.

When it comes to behaviour, though, the parallels frequently become distant, or examples of convergent evolution. The fact that a chimpanzee uses a stick to winkle out a fat grub from the bark of a tree is a trick independent of the same ability in Caledonian crows, whose skills are frequently the source of increasing wonder as we study them more.

What this inevitably means is that using tools is a trick that has been acquired many times in evolution, and it is virtually impossible to assume a single evolutionary antecedent from which this behaviour sprang.

Chimps sharpen sticks with their teeth with which to kebab sleeping bush babies. There is no evidence that these similar behaviours show continuity through time. Arguments around these issues are generally the preserve of scientists. But there is a set of behaviours that are also inspected forensically and with evolution in mind whose reach extends far beyond the academy. Most animals are sexual beings and the primary function of sex is to reproduce. The statistician David Spiegelhalter estimates that up to ,, acts of human heterosexual intercourse take place per year in Britain alone — roughly , per hour.

Our stone tools became more intricate. One study proposes that our technological innovation was key for our migration out of Africa. We started to assign symbolic values to objects such as geometrical designs on plaques and cave art. By contrast, there is little evidence that any other hominins made any kind of art.

One example, which was possibly made by Neanderthals, was hailed as proof they had similar levels of abstract thought. However, it is a simple etching and some question whether Neanderthals made it at all. The symbols made by H. We had also been around for , years before symbolic objects appeared so what happened? We had the capacity for art early in our history Credit: SPL. Somehow, our language-learning abilities were gradually "switched on", Tattersall argues.

In the same way that early birds developed feathers before they could fly, we had the mental tools for complex language before we developed it. We started with language-like symbols as a way to represent the world around us, he says.

For example, before you say a word, your brain first has to have a symbolic representation of what it means. These mental symbols eventually led to language in all its complexity and the ability to process information is the main reason we are the only hominin still alive, Tattersall argues. It's not clear exactly when speech evolved, or how. But it seems likely that it was partly driven by another uniquely human trait: our superior social skills. Comparative studies between humans and chimps show that while both will cooperate, humans will always help more.

Children seem to be innate helpers. They act selflessly before social norms set in. Studies have shown that they will spontaneously open doors for adults and pick up "accidentally" dropped items. They will even stop playing to help. Their sense of fairness begins young. Even if an experiment is unfairly rigged so that one child receives more rewards, they will ensure a reward is fairly split.

Children show 'proactive' kindness, unlike our close relatives Credit: Thinkstock. We know that chimpanzees also work together and share food in apparently unselfish ways. However, Michael Tomasello of the Max Planck institute for Evolutionary Anthropology in Leipzig, Germany, says they will only cooperate if there is something in it for them.

In some experiments we have children as young as months who seem to expect their partner to collaborate in certain ways and who share in ways chimps don't. Human children are less selective about who they share with. Chimpanzees though, largely only share with close relatives, reciprocating partners or potential mates.

Children are "proactive", that is, they help even when presented with only very subtle cues. Chimpanzees though, need more encouragement. They are "reactive": they will hand over objects but only after some nudging. We also possess a descended hyoid bone — this horseshoe-shaped bone below the tongue, unique in that it is not attached to any other bones in the body, allows us to articulate words when speaking.

Humans are unique among the primates in how walking fully upright is our chief mode of locomotion. This frees our hands up for using tools. Unfortunately, the changes made in our pelvis for moving on two legs, in combination with babies with large brains, makes human childbirth unusually dangerous compared with the rest of the animal kingdom. A century ago, childbirth was a leading cause of death for women. The lumbar curve in the lower back, which helps us maintain our balance as we stand and walk, also leaves us vulnerable to lower back pain and strain.

We look naked compared to our hairier ape cousins. Surprisingly, however, a square inch of human skin on average possesses as much hair-producing follicles as other primates, or more — humans often just have thinner, shorter, lighter hairs. Fun fact about hair: Even though we don't seem to have much, it apparently helps us detect parasites , according to one study. Humans may be called "naked apes," but most of us wear clothing, a fact that makes us unique in the animal kingdom, save for the clothing we make for other animals.

The development of clothing has even influenced the evolution of other species — the body louse, unlike all other kinds, clings to clothing, not hair. From pigments to printing presses, symbols changed the way humans lived and provided new ways to cope with an unpredictable world. Within just the past 12, years, our species, Homo sapiens , made the transition to producing food and changing our surroundings. We have been so successful that we have inadvertently created a turning point in the history of life on Earth.

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