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(Image: Jonny Wan)

Two million years ago we were just your average primate – then we started to have some revolutionary ideas and human evolution went into hyper-drive

What makes us human?

IT WAS at least 7 million years ago that our ancestors diverged from those of our closest living relatives, the chimpanzees. For most of that time they were ape-like forest dwellers, with the furry bodies, small brains and unsophisticated behaviour to match. Then, about 2 million years ago, everything changed. We began to take evolution into our own hands, starting a series of innovations that changed human history – and made us into the very modern apes we are today (see timeline below).

Cooking

Our earliest ancestors may have walked on two legs, but their heads were small, their teeth large and their arms long. No one knows for sure why they began to look more human, but unlike the bodies of other species, which are shaped by natural selection, ours may have been sculpted by our own ingenuity.

Here’s the theory. Early hominins dined on tough, raw foods that required a lot of chewing and digesting to break down. That changed when they began to control fire and cook. Heat softens food and breaks down difficult-to-digest fibre into easily absorbed sugars. Big teeth and long guts were no longer necessary, and so over the generations they gradually shrank. Other things shrank too. Because fire wards off predators, our ancestors did not have to retreat to the trees at night and no longer needed such long arms for climbing. Finally, the energy savings made by shrinking body parts went to their heads; their brains began to grow. In other words, Homo erectus looked like us because it cooked like us.

Richard Wrangham at Harvard University has been . “I have not seen any alternative proposals for how H. erectus acquired small molars, small guts and terrestrial sleeping,” he says. But the idea is not without its problems. Most obviously, while the anatomical changes started some 2 million years ago, the oldest evidence of controlled fire use is just 1 million years old. “I am quite sympathetic to the cooking hypothesis,” says Michael Chazan at the University of Toronto in Canada, whose team discovered the ancient deposits of ash and burnt bone in a cave in South Africa in 2011. “But H. erectus may have had less complete reliance on cooking [than later species of humans].”

An alternative idea pins brain growth on a shift to eating meat, which would provide a more nutritious diet. It implies H. erectus was a skilled hunter. until it is totally exhausted. But another ancient human innovation reshaped the rules of the hunt – and perhaps the nature of human societies too.

Weapons

Projectile weapons travel faster than even the speediest antelope. A study published last year suggested that H. erectus made use of them, since it was the earliest of our ancestors with a shoulder suitable for powerful and accurate throwing. What’s more, at a H. erectus site near the town of Dmanisi in Georgia give an idea of their projectile weapon of choice.

But throwing rocks did more than offer a new hunting strategy: it also gave early humans an effective way to kill an adversary. Christopher Boehm at the University of Southern California has suggested that projectile weapons levelled the playing field in early human societies by allowing even the weakest group member to take down a dominant figure without having to resort to hand-to-hand combat. So weapons, he argues, encouraged early human groups to embrace an egalitarian existence unique among primates; one that is still seen in hunter-gatherer societies today.

In fact, weapons may have had an even greater impact. Paul Bingham and Joanne Souza at Stony Brook University in New York have developed the idea that human societies used, and continue to use, the threat of projectile weapons to encourage a high level of cooperation among group members. They call it the social coercion theory.

Jewellery and cosmetics

If Bingham and Souza are right, we would recognise some of our social behaviour in H. erectus. However, it is not until 100,000 years ago – after the appearance of Homo sapiens – that many of our most recognisable habits began to form.

At the Blombos cave in South Africa, excavations a decade ago revealed collections of shells that had been perforated and stained, and then strung together to form necklaces or bracelets. Similar finds have now turned up at other sites in Africa. More recently, work at Blombos has uncovered evidence that ochre was deliberately collected, combined with other ingredients and fashioned into body paint or cosmetics.

At first glance these inventions seem trivial, but they hint at dramatic revolutions in the nature of human beliefs and communication. Jewellery and cosmetics were probably prestigious, suggesting the existence of people of higher and lower status and challenging the egalitarian sensibilities that had existed since the early days of H. erectus. More importantly, they are indications of symbolic thought and behaviour because wearing a particular necklace or form of body paint has meaning beyond the apparent. As well as status, it can signify things like group identity or a shared outlook. That generation after generation adorned themselves in this way indicates these people had language complex enough to establish traditions.

Sewing

What people invented to wear with their jewellery and cosmetics was equally revolutionary. about 60,000 years ago, providing the first evidence of tailoring, but humans had probably already been wearing simple clothes for thousands of years. Evidence for this comes from a rather unusual source. Body lice, which live mostly in clothes, evolved from hair lice sometime after humans began clothing themselves, and a suggests body lice arose some 70,000 years ago. puts their origin as early as 170,000 years ago. Either way, it looks like we were wearing sewn clothes when we migrated from our African cradle some 60,000 years ago and began spreading across the world.

Mark Stoneking at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, an author on the original louse study, suggests that clothes would have allowed humans to inhabit cold areas that their naked predecessors could not tolerate. Sewing could have been a crucial development, since fitted garments are more effective at retaining body heat than loose animal furs. Even then, the frozen north would have been a challenge for a species that evolved on the African savannah, and recent research indicates that we also took advantage of changes in the climate to spread across the world.

Containers

When some of our ancestors left Africa, they probably travelled with more than just the clothes on their backs. About 100,000 years ago, people in southern Africa began using ostrich eggs as water bottles. Having containers to transport and store vital resources would have given them huge advantages over other primates. But engravings on these shells are also highly significant: they appear to be a sign that dispersed groups had begun to connect and trade.

Since 1999, Pierre-Jean Texier at the University of Bordeaux in France has been uncovering engraved ostrich egg fragments at the Diepkloof rock shelter, 150 kilometres north of Cape Town in South Africa. The same five basic motifs are used time and again, over thousands of years, implying they had a meaning that could be read and understood across numerous generations. Texier and his colleagues think they show that as they began travelling further and interacting with other groups.

Law

As our ancestors began trading, they would have needed to cooperate fairly and peacefully – with not just group members but also strangers from foreign lands. So trade may have provided the impetus to invent law and justice to help keep people in line.

Hints of how law evolved come from modern human groups, which, like Stone Age hunter-gatherers, live in egalitarian, decentralised societies. The Turkana are nomadic pastoralists in east Africa. Despite having no centralised political power, the men will cooperate with non-family members in a life-threatening venture – stealing livestock from neighbouring peoples, say. While the activity itself may be ethically dubious, the motivation to cooperate reflects ideas that underpin any modern justice system. If men refuse to join these raiding parties they are judged harshly and punished by other group members, says Sarah Mathew at Arizona State University in Tempe. “They display mechanisms of adjudication and punishment akin to formal judiciary, suggesting that law and justice predates the emergence of centralised societies.”

Timekeeping

As trade flourished over the millennia that followed, it wasn’t just material goods that were exchanged. Trade in ideas encouraged new ways of thinking, and perhaps the early stirrings of scientific thought. Communities of hunter-gatherers living in what is now Scotland may have been among the first to scientifically observe and measure their environment. Aberdeenshire has many Mesolithic sites dating from about 10,000 years ago, including an odd monument consisting of a dozen pits arranged in a shallow arc trending roughly north-east to south-west. When Vincent Gaffney at the University of Birmingham and his colleagues noticed the arc faced a sharp valley on the horizon through which the sun rises on the winter solstice, . The 12 pits were almost certainly used to keep track of lunar months. The Aberdeenshire lunar “calendar” – or “time reckoner” as they dubbed it – is comfortably twice the age of any previously found.

“The ideas that transformed us may also have sown the seeds for future revolutions”

“Almost every culture begins to define the passing of time using the moon,” says Gaffney. By establishing a formal concept of time you know when to expect seasonal events, such as the return of salmon to the local rivers. And knowledge is power. “If you have that arcane knowledge you have the opportunity to control society,” says Gaffney.

Ploughing

While Scotland’s hunter-gatherers were measuring time, their contemporaries in the Near East had settled down to farm. Crop cultivation is tough work that inspired the first farmers to invent labour-saving devices. The most quintessential of these, the plough, might have influenced society in a surprising way.

In the past, as today, hunter-gatherer societies were probably often divided along gender lines, with men hunting and women gathering. Farming promised greater gender equality, because both sexes could work the land, but the plough – which was heavy and so primarily controlled by men – brought an end to that. So . Last year Paola Giuliano at the University of California, Los Angeles, and her colleagues by comparing gender equality in societies across the world that either adopted the plough or a different form of agriculture. Not only did they confirm the plough effect, they found that it continues to influence gender perceptions today. “The plough is not the only determinant of differences in gender roles,” stresses Giuliano. “But if two societies are otherwise alike, those that use the plough will be more gender-biased.”

Sewerage

it is back-breaking work. But it did provide such plentiful food that it allowed the growth of urban centres. City living comes with many advantages but it also carries a health warning; urbanites are at risk from infectious diseases carried by water.

Almost as long as there have been cities, there have been impressive sewerage systems. . dating from around the same time, and . But none of these were really designed with sanitation in mind, says Thomas Bond at Imperial College London. “Many of the sewerage systems were advanced in a civil engineering sense, but they were really just to dispose of waste water – for example into the nearest river.”

It was only in the 1850s, when physician John Snow linked an outbreak of cholera in London to insanitary water supplies, that people started to clean waste water. Large-scale centralised sewage works date from the early decades of the 20th century. Effective sewerage was a long time coming, but when it did arrive it revolutionised public health.

Writing

The engraved ostrich eggshells of Diepkloof show that modern humans have used graphical symbols to convey meaning for at least 100,000 years. But . Now people could record information and pass it between places and generations. Cultural evolution would never be the same again.

Writing also provided a means to convey hopes and fears, revealing how subsequent innovations had affected the human psyche. Some of the world’s oldest texts, from the Mesopotamian city-state of Lagash, rail against the spiralling taxes exacted by a corrupt ruling class. Soon afterwards, King Urukagina of Lagash wrote what is thought to be the first documented legal code. He has gained a reputation as the earliest social reformer, creating laws to limit the excesses of the rich, for instance, but his decrees also entrench the inferior social position of women. One details penalties for adulterous women, but makes no mention of adulterous men. Despite all our revolutionary changes, humanity still had some way to go.

This article appeared in print under the headline “Transformers”