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Book Summary: The Book of Humans: A Brief History of Culture, Sex, War and the Evolution of Us

Author: Adam Rutherford

Substory: Evolution

Evolution is slow, and the Earth has been host to life for the vast majority of our planet’s existence. The timescales we talk about so casually in science are utterly baffling to comprehend. Even though we are a latecomer to life on Earth, our species is more than 3,000 centuries old. We have traversed that ocean of time largely unchanged. Physically, our bodies are not drastically different from Homo sapiens in Africa 200,000 years ago.2 We were physically capable of speaking then as we do today, and our brains were not significantly different in size. Our genes have responded in small part to changes in the environment and diets as we migrated within and out of Africa, and genetic variants account for the minuscule percentage of DNA that spells out the differences between individuals, changes in the most superficial characteristics – skin colour, hair texture and a few others. But if you tidied up a Homo sapiens woman or man from 200,000 years ago, gave them a haircut and dressed them in twenty-first-century clothes, they would not look out of place in any city in the world today.

There’s a conundrum in that stasis. Though we may not look different, humans did change, and profoundly. There’s debate about when this transition occurred, but by 45,000 years ago, something had happened. Many scientists think that it was a sudden change – sudden in evolutionary terms means hundreds of generations and dozens of centuries, rather than a thunderbolt. We don’t quite have the language to relate to the timescales involved in such transitions. But what we can observe from the archaeological record is that we see the emergence and accumulation of a number of behaviours that are associated with modern humans, and there was a time before that where we see fewer or none of them. Given how long life has existed on Earth, this switch happened relatively in a heartbeat.

The transformation occurred not in our bodies or physiology or even in our DNA. What changed was culture. In scientific terms, culture refers broadly to the artefacts that are associated with a particular time and place. They include things like tools, blade technology, fishing gear, and use of pigment for decorative purposes or jewellery. The archaeological remains of a hearth show the ability to control fire, to cook, and maybe its position as a social hub. From material culture, we can infer behaviour. From fossils we can try to piece together what people looked like, but with archaeological evidence of the paraphernalia of our ancestors’ lives, we can address what people were like in prehistory, and when they became like that.

By 40,000 years ago, we were designing decorative jewellery and musical instruments. Symbolism in our art was rife, and we were inventing new weapons and hunting technology. Within a few millennia, we had fostered dogs into our lives – tamed wolves that accompanied our search for food long before they became our pets.

The concatenation of these behaviours is sometimes referred to as the Great Leap Forward, as we jumped into a state of intellectual sophistication that we see in ourselves today. Alternatively, it’s a ‘cognitive revolution’, but I dislike the use of that phrase to describe a process which was both continuous and probably lasted a few thousand years or more – real revolutions should be thunderbolts. Nevertheless, modern behaviour emerges permanently and quickly in several locations around the world. We began to carve complex figurines, both realistic and abstract, sculpted make-believe chimeras out of ivory, and we adorned cave walls with pictures of hunts, and of animals important to our lives. The earliest piece of figurative art by Homo sapiens that we know of is a 40,000-year-old twelve-inch statue of a lean man with the head of a lion. It was carved from a mammoth tusk during the last Ice Age.

Soon after that time we were making small statues of women. They are known today as Venus figurines. We don’t know if there was a specific purpose to these dolls, though some researchers think they may have been fertility amulets, as their sexual anatomy is exaggerated: bosomy women with swollen labia, and often bizarrely small heads. Maybe they were just art for art’s sake, or toys. Either way, to create such sculptures requires great skill and foresight, and a capacity for abstract thought. A lion-man is an imagined being. The Venus amulets are deliberate misrepresentations, abstractions of human bodies. These figures cannot exist in isolation either: artisan craft requires practice, and though today only a handful of these beautiful works of art remain, they must represent an iterative process, a lineage of skilled craftspeople.

Some of these types of traits pop up before the full transition to our modern behaviour, but they do so fleetingly, and then vanish from the archaeological record. Homo sapiens were not the only humans to have existed in the last 200,000 years, and not the only ones to have refined culture. Homo neanderthalensis, far from the brutes of popular lore, were simply people too. We are wrong to think of them as merely upright apes, living in dust with crude language and tools, all set for extinction. Neanderthals showed clear signs of modern behaviour: they made jewellery, employed complex hunting techniques, used tools, had a control of fire, and made abstract art. We have to consider that they also were sophisticated in a way indistinguishable from our direct Homo sapiens ancestors, which undermines the uniqueness of our own forward leap. Though we have traditionally considered Neanderthals to be cousins to us, they were also ancestors: we now know that our lineage and theirs diverged more than half a million years ago, and both groups were isolated in time and space for almost all of that period. But our ancestors left Africa some 80,000 years ago, and were immigrants into Neanderthal territory. We reached Europe and central Asia, and around 50,000 years ago, we bred with them. Their bodies were different enough that they lie outside the range of human physical diversity as we see it today – a bit less chin, a bit more chest, heavy-set brows and robust faces. They weren’t so different that we didn’t have sex with them, women and men from both sides of the species fence, and together we had children. We know this because our genes are in their bones, and theirs are in our living cells. Most Europeans carry a small but significant percentage of DNA that was acquired from Neanderthals, and this blurs any hope of a clear boundary between two sets of people that we have declared separate species – that is, organisms that cannot produce fertile offspring. Though Neanderthal DNA is slowly being purged from our genomes for reasons that are not fully understood, humans today bear their living genetic heritage, as we do the genes of another type of human, the Denisovans, further to the east, and maybe others that are yet to be discovered but whose legacy sits within our DNA.

When we first met, the Neanderthals and those other people were not long for this world, and by around 40,000 years ago, Homo sapiens had outlived the last of them. Whether the Neanderthals had undergone a full transition to the behavioural modernity as we saw in Homo sapiens, we do not know, and may never know, but the evidence is pointing towards those cavemen and women being much like ourselves in every way.

We lived and they died. We don’t know what gave Homo sapiens the edge over Neanderthals. All life is set for extinction over a long enough timescale: more than 97 per cent of species that have ever existed are already gone. The Neanderthals’ tenure on Earth was much longer than we have racked up so far, and we are yet to firmly understand why their light was finally snuffed out 40,000 years ago. We don’t think there were ever very many Neanderthals, which may have contributed to their demise. Maybe we outsmarted them. Maybe we brought with us diseases that we had lived with and earnt immunity to, but which were lethal to a virgin population. Maybe they simply petered out of existence. What we do know though is that around this time, the last type of human began to permanently and globally show signs of who we are today.

We certainly outbred all our nearest relatives. Homo sapiens went forth and multiplied very effectively. We’re the dominant life form on Earth by many measures, if ranking matters to you (though bacteria outnumber us – you carry more bacterial cells than human ones – and are far more successful in terms of longevity. They have a four-billion-year lead on us, and no prospect of extinction). Today there are upwards of seven billion humans alive, more than at any time in history, and that number is still rising. Through our ingenuity, science and culture, we have eradicated many diseases, drastically reduced infant mortality, and extended lifespan by decades.