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Our closest cousins
Our species came into existence some time within the last 500,000 years. But it was not alone. At least some of the older, more ‘primitive’ species like Homo naledi were still around. What’s more, several other hominin species had evolved. These were not primitives: in at least one case, the Neanderthals, they were almost as smart and capable as we are. In fact, our ancestors may not even have been conscious of a difference and, even if they were, it didn’t stop them having sex with these distant relatives.
Neanderthal minds
The most famous (and most misunderstood) extinct hominins of them all are the Neanderthals. Ever since the first fossils of a brawny, low-browed, chimp-chested hominin were unearthed in Germany in 1856, Neanderthals have stirred both fascination and disdain. German pathologist Rudolf Virchow decreed that the bones belonged to a wounded Cossack whose brow ridges reflected years of pain-driven frowns. French palaeontologist Marcellin Boule recognized the fossils as ancient, but ignored signs that the specimen he studied suffered from arthritis. It was he who reconstructed the bent-kneed, shambling brute that still lurks in the back of most people’s minds. Irish geologist William King found the creature so ape-like that he considered putting it into a new genus. In the end, he merely relegated it to a separate species, Homo neanderthalensis.
Since then, hundreds of Neanderthal sites have been excavated. These show that Neanderthals occupied much of modern-day Eurasia, from the British Isles to Siberia, and from the Red Sea to the North Sea. Here they survived 200,000 years or more of climatic chaos before eventually disappearing perhaps as recently as 30,000 years ago.
The long-held view that Neanderthals were inferior to Homo sapiens is changing as, one by one, capabilities thought to be unique to us have been linked to them. What is more, the two species clearly crossed paths: publication of the Neanderthal genome in 2010 shows that they interbred. In fact, we share more than 99 per cent of our genes with Neanderthals.
If our ancestors made love, not war, the same cannot be said for the researchers who study them. The new discoveries have been pounced upon by those who believe Neanderthals thought like we did, talked like we did and enriched their world with music, decoration and symbols as we did. It has even been suggested that we are the same species. However, there are still some who vehemently argue that Neanderthal minds were no match for those of our H. sapiens ancestors. Surprisingly, they, too, point to the latest genetic evidence to bolster this view. So, were Neanderthals once our equal, or just another failed species of hominin?
The first pieces of evidence to support the revisionist camp come from Neanderthal lifestyles, which indicate parallels with early modern humans. We know, for example, that in addition to occupying caves and overhangs, Neanderthals also constructed shelters. Holes for wooden pegs and posts that probably supported lean-tos have been found at two sites in France. Numerous hearths dating from 60,000 years ago indicate that Neanderthals also controlled fire. They may, however, have been the first to play music around their fires. The oldest known musical instrument has been attributed to Neanderthals by its discoverer Ivan Turk, although sceptics argue that the 43,000-year-old bone ‘flute’ found at Divje Babe in Slovenia is just a cave bear femur punctured by wild animals.
There is also evidence that Neanderthals wore clothes. And some claim that, like today’s traditional Inuit, they softened animal skins with their teeth.
Initially seen as mere scavengers, it is now clear that Neanderthals hunted formidable prey, including rhinos and fully grown mammoths. They also adapted their hunting strategies to the environment, ambushing solitary prey in forests, stalking bison and other herd animals on the steppes, and harvesting birds, rabbits and seafood at the shore.
Their toolkit, dating from between 300,000 and 30,000 years ago, required planning, concentration and great skill to make. Meticulous preparation of a stone core was needed so that a final rap from a hammer stone would yield a predetermined flint flake tool. They even manufactured and used compound tools made from more than one material, including some of the first hafted spears, some 127,000 years ago. There is evidence dating from 80,000 years ago that they created a kind of glue from heated birch pitch to attach stone points to spear hafts.
In the past it was generally believed that advances in Neanderthal technology towards the end of their era were simply copied from early modern humans, but research from 42,000-year-old Neanderthal sites in southern Italy refutes this. There, at least, Neanderthals developed an array of stone and bone tools distinct from those used by the early humans living further north. Although Neanderthals have been typecast as incapable of change, many researchers now accept that they did innovate.
There is also widespread acceptance that Neanderthals buried their dead. The earliest undisputed H. sapiens burial is in Skhul Cave, on Mount Carmel, Israel, and dates to around 120,000 years ago. Neanderthal burials have been found at several sites, including La Chapelle-aux-Saints in France, where the ‘Old Man’ was interred with coloured earth around 60,000 years ago (see Figure 5.1), and Teshik-Tash in Uzbekistan, where a nine-year-old boy was buried encircled by ibex horns some 70,000 years ago. Dating from around the same time are the graves of ten individuals found at Shanidar Cave in Iraq. Ian Tattersall from the American Museum of Natural History in New York, author of Extinct Humans (2001), notes that one of these burials reveals that Neanderthals took care of an injured individual for years before his death, providing ‘powerful, presumptive evidence for empathy and caring within the social group, and possibly for complex social roles’.
FIGURE 5.1 Neanderthals were far more advanced than was first thought. They even buried their dead, as here at La Chapelle-aux-Saints in France.
Shanidar is also the location of the famous ‘flower burial’. The high concentration of pollen from medicinal plants in this grave is sometimes cited as evidence of shamanism and ritualistic funerary practices by Neanderthals. Although this interpretation has been disputed, other evidence has bolstered the case for the Neanderthals’ capacity for symbolic thought.
In 2010 researchers reported that they had found perforated seashells, red and yellow pigments, and shells encrusted with a mixture of several pigments in two caves in Spain, one of them 60 kilometres from the sea. This, they claim, shows that Neanderthals adorned themselves with symbolic artefacts and that, since these date back 50,000 years, before modern humans arrived in the area, they also represent independent Neanderthal innovations.
Symbolic thought is often associated with another characteristically human trait: language. Ralph Holloway at Columbia University in New York believes that Neanderthals could speak. He has studied hundreds of brain casts from fossilized Neanderthal skulls and found that, even accounting for their big bodies, their brain size is within a few per cent of that of modern humans and, despite their sloping brows, they had frontal lobes and speech areas like ours.
As well as these physical clues, genetic tests reveal that Neanderthals had a version of a gene called FOXP2 that is associated with language in humans. Meanwhile, fossils from Kebara Cave in Israel show that the Neanderthal hyoid, a U-shaped bone in the neck that anchors key speech muscles, matched ours.
Philip Lieberman, a linguist at Brown University in Providence, Rhode Island, agrees that Neanderthals had speech. However, he argues that before around 50,000 years ago neither Neanderthals nor modern humans could produce the full range of sounds that we can today. Having studied skulls ranging from 1.6-million-year-old Homo erectus through to 10,000-year-old H. sapiens, Lieberman concludes that neither species was capable of the vowel sounds in ‘see’, ‘do’ and ‘ma’. Given this accruing evidence, many anthropologists now believe that Neanderthals probably had the same range of mental abilities as modern humans do.
You might think that the case must be closed, but some researchers still disagree with this wholesale reappraisal. Neanderthals and modern humans diverged 500,000 years ago and evolved separately in Europe and Africa. Cumulatively, that represents a million years of evolution. Given that, you would expect that there would be changes in their brains and therefore cognitive differences.
The publication in 2010 of the first Neanderthal genome lent some support to this argument. Although there is a less than 1 per cent difference between the genomes of today’s humans and those of Neanderthals, this could equate to mutations in hundreds of genes.
Neanderthals may have had subtle cognitive shortcomings. It has been claimed that their lifestyles show little forward planning, and that they had less working memory capacity than modern humans, limiting the amount of information they could process at any given time. Steven Mithen, an archaeologist at the University of Reading, UK, grants Neanderthals modern capacities in knowledge of the natural world, manipulating materials and social interaction. However, he has argued that they lacked the ‘cognitive fluidity’ and ‘capacity for metaphor’ to link these domains, leaving them unable to produce complex symbolic objects.
However, for most of this period, early modern humans were not that innovative, either. There are few differences between their accomplishments and those of Neanderthals up until about 50,000 years ago. At this point, however, early modern humans pulled away, undergoing a ‘big bang’ of symbolic activity typified by carved statuettes, elaborate burials, an abundance of personal decorations and, eventually, elaborate cave paintings. It may be that, by the time modern humans entered Europe, they had better technology, better social organization and better brains.
Surprising talents
The list of abilities Neanderthals have demonstrated grows with every passing year, and it includes some startling tricks. For instance, they seem to be responsible for the earliest evidence of string in the archaeological record.
Perishable materials usually rot away, so the oldest string on record dates back only 30,000 years. But perforations in small stone and tooth artefacts from Neanderthal sites in France suggest that the pieces were threaded on string and worn as pendants. Similar circumstantial evidence has been found in perforated shells.
At 90,000 years old, the material purported to be string predates the arrival of Homo sapiens in Europe. This implies that the Neanderthals occupying the French site learned to make it themselves, rather than imitating modern humans.
Neanderthals also had the brains and guile to catch and eat birds – a skill many had assumed was beyond them. Bones found at Gorham’s Cave in Gibraltar and described in 2014 suggest that Neanderthals hunted wild pigeons – rock doves – possibly by climbing steep cliffs to reach their nests. The dove bones were buried in sediments laid down between 28,000 and 67,000 years ago. Most of the excavated layers date from a time when only Neanderthals lived in the area, before the arrival of modern humans around 40,000 years ago. This means that only Neanderthals could have caught the birds.
The first artists?
Speaking of Gorham’s Cave in Gibraltar, there are scratches on one part of the cave floor. They look like a hashtag, or a game of Stone Age tic-tac-toe. No one is quite sure what they really mean. But two things seem reasonably clear: the scratches are the work of a Neanderthal and they were made quite purposefully more than 40,000 years ago.
The etchings were discovered by Clive Finlayson of the Gibraltar Museum and colleagues, whose team also unearthed the rock dove bones. The age of the thick layer of clay that lies immediately on top of the rock – itself littered with Neanderthal tools and remnants of the fires they burned – tells us that the etching was made at least 39,000 years ago.
It seems clear that the etching was done with a purpose. Finlayson’s colleague Francesco d’Errico from the University of Bordeaux carried out experiments to determine whether the scratches could have been made by accident. Using two kinds of Neanderthal rock points as his stylus and a slab of rock identical to the floor of the cave as his canvas, he needed to make in excess of 100 strokes to reproduce the pattern exactly.
What divides opinion is what it all means. Some say that the etchings are abstract symbols of some description, bolstering the notion that Neanderthals were capable of subtle symbolic thought. Others remain to be convinced.
Researchers have since described evidence for some rather different Neanderthal relics: a set of stone structures. In one chamber of Bruniquel Cave near Toulouse in south-west France, 336 metres from the cave entrance, there are enigmatic structures – including a ring 7 metres across – built from stalagmites snapped from the cave floor. Natural limestone growths have begun to cover parts of the structures, so by dating these growths researchers could work out an approximate age for the stalagmite constructions. They are roughly 175,000 years old, when Neanderthals were the only hominins in the region.
Today we can only guess as to why they built the circles – but the fact that they did provides a rare glimpse into their potential for social organization in a challenging environment.
The great extinction
Everyone, it seems, has a different idea about why the Neanderthals became extinct.
Those who see them as an inferior species suspect that smarter, more talkative, more social and adaptable early modern humans outcompeted Neanderthals in terms of resource use, organization and reproductive success, if not direct confrontation.
Those who believe that Neanderthals were just as smart as early humans typically look to climate change, natural catastrophes and cumulative cultural differences to explain the extinction. In his 2009 book The Humans Who Went Extinct, Finlayson argues that the Neanderthals relied on close-up ambush hunting, which was fine when Europe was covered in forests but became a problem when the forests shrank. As their habitat diminished, the Neanderthals became vulnerable to threats such as disease and competition.
Of course, they may also just have been unlucky.
Perhaps the first issue to settle is when the Neanderthals died out, as that should help us eliminate a few possibilities. A 2014 reassessment of major archaeological sites suggests that instead of dying out 23,000 years ago, as many had believed, Neanderthals were gone as early as 39,000 years ago. It also looks as if we shared their territory for 5,000 years, steadily replacing them as we spread across Europe.
This seems to support the idea that our direct ancestors pushed Neanderthals out.
The researchers who carried out the reassessment used improved techniques to date material from 40 key sites in Europe, spanning the period when humans reached Europe and Neanderthals vanished. Every possible or definite Neanderthal site was at least 40,000 years old. In other words, Neanderthals had largely, and perhaps entirely, vanished from their known range by 39,000 years ago. There are Neanderthal artefacts claimed to be 23,000 years old, but the team could not get any solid dates from them, so while a late survival is possible, there is no real evidence.
But that does not mean we murdered our cousins. There is no evidence humans ever killed Neanderthals, and they may not have met very often. So what role did we play? Many now suspect that we were the last straw for an already fragile species. For much of their 400,000-year history, Neanderthals were few and far between, according to a 2009 analysis of their genetic material.
That conclusion isn’t earth shattering. Archaeological digs suggest that Neanderthals hardly lived in megacities. It’s difficult to put a number on the population of a species based on DNA alone, but less than a few hundred thousand of these archaic humans roamed Europe and Asia at any one time.
What is most obvious is how little genetic heterogeneity they possessed. The mitochondrial genomes of six Neanderthals recovered in Spain, Croatia, Germany and Russia differ at only 55 locations out of more than 16,000 letters. This represents one-third of the mitochondrial diversity of modern humans. Because of this low diversity, Neanderthal populations must have been relatively small.
The researchers analysed bone samples that, by and large, came during the twilight of the Neanderthal’s reign around 40,000 years ago. They may have obtained a genetic snapshot of a species on the verge of extinction. However, other genetic clues indicate that Neanderthal populations stayed low for much of their history.
The power of wolves
US palaeoanthropologist Pat Shipman believes that one key to our success at displacing the Neanderthals was our partnership with a weapon that wagged its tail: the domestic dog. Thanks to dogs, we may have been better at hunting than they were.
Until recently, no one thought domestic dogs appeared until about 15,000 years ago. But in 2009 a research team began investigating ways to tell dogs apart from wolves using statistical methods. These two canids are so similar that they can and do interbreed; no simple genetic or physical trait distinguishes them. However, a complex analysis of skull shape reliably separates wolves from both modern dogs and from accepted prehistoric wild dogs. Analysing additional fossil canid skulls, the team recognized a group of ancient dog-like animals intermediate in shape between wolves and prehistoric dogs. Shipman calls them ‘wolf-dogs’, not because she believes they were hybrids but because deciding which group they belonged to is not easy.
Whatever wolf-dogs were, they were different from contemporary wolves. Chemical analysis of their bones shows that their diets differed from those of humans or wolves at the same sites. Wolf-dog mitochondrial DNA differs from that of any other canid and is very primitive compared with that of other modern and fossil dogs and wolves.
The oldest wolf-dog yet identified is 36,000 years old, much older than expected for a domesticated animal. All known wolf-dogs occur in sites created by humans, not Neanderthals. The sites contain the bones of dozens, even hundreds, of woolly mammoths, although mammoths were previously rare in archaeological sites. Some were clearly hunted, their bones butchered, skinned and charred. The sites include hearths, tools and huts built from mammoth bones.
Although top predators are always rare in ecosystems, wolf remains at these sites are so abundant that they must also have been targeted. Their luxuriant fur would have been useful in near-Arctic conditions, and territorial wolf-dogs – like wolves and dogs today – would probably not tolerate the presence of any other canid.
Even if wolf-dogs were poorly domesticated, cooperating with them would have offered huge advantages during a hunt.
Written in the genes
In 2010 the story of human evolution had to be rewritten. Geneticist Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and his colleagues announced that they had sequenced the genome of a Neanderthal. That is, they had managed to read all the genes of a Neanderthal – even though it had been dead for tens of thousands of years. This was an astonishing feat. Pääbo’s team had pioneered the genetic study of Neanderthals but an entire genome had never been obtained.
It turned out that every human whose ancestral group developed outside Africa has a little Neanderthal in them – between 1 and 4 per cent of their genome. In other words, humans and Neanderthals had sex and had hybrid offspring. A small amount of that genetic mingling survives in ‘non-Africans’ today: since Neanderthals did not live in Africa, sub-Saharan African populations show no trace of Neanderthal DNA.
The interbreeding seemed to have happened around 50,000 years ago. That is because all non-Africans – be they from France, China or Papua New Guinea – share the same amount of Neanderthal DNA, suggesting that interbreeding occurred before those populations split. The timing makes the Middle East the likeliest location: humans who were leaving Africa could have met resident Neanderthals and done the deed.
Even more Neanderthal sex
Since 2010 we have learned that there have been several occasions when humans and Neanderthals interbred: not just that one period 50,000 years ago in the Middle East.
For instance, it turns out that some Neanderthals carried our DNA. One group had a big chunk of modern human DNA right in the middle of the gene that may have a role in language development, called FOXP2. What’s more, they got that DNA from us at least 100,000 years ago. This might have happened in the Arabian Peninsula or the eastern Mediterranean, based on tentative archaeological evidence that modern humans were living in those regions by then.
In 2017 evidence emerged of an even earlier interbreeding episode. DNA from modern humans turned up in a Neanderthal fossil in Germany from 124,000 years ago. This was odd, because modern humans were not supposed to have reached Europe until about 60,000 years ago. The proposed explanation is that there was a previous migration of early humans – more than 219,000 years ago.
This would mean that modern human ancestors must have interbred with Neanderthals before 219,000 years ago – and must have migrated out of Africa into Europe much earlier than we thought.
The Denisovans
The ability to reconstruct DNA from extinct organisms has not just enabled us to study known species. It has also revealed an entire new hominin species.
The story begins in 2008, with a tiny fragment of finger bone discovered in Denisova Cave in the Altai Mountains of southern Siberia. Michael Shunkov from the Russian Academy of Science bagged and labelled the shard, and sent it off for analysis. At his lab in Leipzig, Svante Pääbo was perfectly placed to show that it belonged to a Neanderthal.
But they were all in for a surprise. The Siberian genome was quite unlike the Neanderthal’s and it did not match that of any modern human. It was something completely new. Here was evidence that a previously unimagined species of humans had existed some 50,000 to 30,000 years ago – around the time when our own ancestors were painting masterpieces in the Chauvet Cave in France.
A few years on, the new species has a moniker – Denisovan, after the cave. Our picture of these mysterious people is still being painstakingly pieced together. That first sliver of bone, together with a few teeth, is all we have to go on – there is still no body – but what these meagre remains have revealed is remarkable.
Within months, David Reich of Harvard Medical School in Boston, Massachusetts, working with Pääbo, had a draft of the Denisovan genome. It showed that the Denisovans were a sister group to Neanderthals. Their common ancestor branched off from our lineage, perhaps around 600,000 years ago. Then the Denisovans split from Neanderthals some 200,000 years later, perhaps parting ways in the Middle East, with Neanderthals heading into Europe and Denisovans into Asia. Given how recent the Denisova Cave specimen is, it is quite plausible that the Denisovans were around for some 400,000 years – much longer than modern humans have existed so far.
With the bone sliver proving so enlightening, the hunt was on for more remains. In 2010 DNA analysis of a forgotten tooth found in the Denisova Cave in 2000 revealed that it, too, was Denisovan. Suddenly, there were two fossils.
Archaeologists love teeth because they can reveal so much about an animal’s body and habits, especially its diet. The specimen, a third molar – a wisdom tooth from the back of the mouth – should have been a vital clue, but it was singularly baffling. At almost 1.5 centimetres across, it is huge. That marks it as primitive: our apelike ancestors had larger teeth because they needed to grind up tough food like grasses. But by 50,000 years ago humans were eating softer foods and their teeth had shrunk. The Denisovan tooth looks like a throwback. Still, hominins with unusual teeth do sometimes crop up, and wisdom teeth are the most variable in the jaw, so this enormous one could simply have been an anomaly.
Then, in August 2010, archaeologists found another large tooth. Bence Viola of the University of Toronto, who was present, thought it belonged to a bear, but genetic analysis showed it to be Denisovan. It, too, was a wisdom tooth, although from a different individual, strengthening the case that Denisovans had weirdly big teeth. That hints at a fibrous, plant-based diet, but evidence for this idea is still lacking.
In 2017 a fourth tooth was identified as Denisovan: a worn milk tooth lost by a girl of 10 to 12 years old. Unearthed in the Denisova Cave in 1984, the tooth came from a geological layer formed between 227,000 and 128,000 years ago, making it potentially the oldest of the specimens.
Meanwhile, the genome had already revealed another secret about the Denisovans – that some of us carry their genes. To find out whether humans and Denisovans interbred, the geneticists looked at the few parts of the genome that vary from person to person, searching for individuals who carry Denisovan versions of these sections. Most of the people they sampled had no sign of Denisovan DNA, even if they were from mainland Asia, where our ancestors might have been expected to run into Denisovans. However, the researchers also sequenced the genome of someone from Papua New Guinea – and found a huge signal. Other Melanesian people also carried Denisovan DNA, with an average 4.8 per cent of their genome coming from Denisovans.
Clearly, interbreeding did occur. But if Denisovans lived in southern Siberia, how on earth did their DNA end up in Melanesia, thousands of kilometres away across open sea? The most obvious explanation is also the most startling: Denisovans ranged over a vast swathe of mainland Asia and they also crossed the sea to Indonesia or the Philippines. This means that they had a bigger range than the Neanderthals.
Alternatively, perhaps they interbred with modern humans on mainland Asia, and the descendants of such encounters later moved south-east, leaving no trace on the mainland. This would mean that the Denisovans were not as widespread as all that.
To find out which theory was correct, Reich sequenced the genomes of indigenous peoples from Asia, Indonesia, the Philippines, Polynesia, Australia and Papua New Guinea. If the interbreeding had happened on mainland Asia before people populated the islands, then people on all those islands should carry some Denisovan genes. But if the Denisovans had reached the islands and interbred with humans already there, some isolated populations might be Denisovan-free. He found the latter pattern, so it is unlikely that interbreeding happened on the mainland.
The genetics, then, is telling us that the Denisovans mated with early modern humans somewhere in South East Asia. If that is true, these people were formidable colonizers. From their origins at the split with Neanderthals, they appear to have made it out of the Middle East, spreading both north into Siberia and east to Indonesia and on to Melanesia.
During the last ice age, between 110,000 and 12,000 years ago, South-East Asia would have been an especially good place to live. Instead of lush forests, there were open grassy spaces. The ice at the poles locked up lots of water, lowering sea levels by tens of metres. As a result, Sumatra and Borneo were part of the mainland.
In other words, we have had the story of the Denisovans backwards: they may be named for a cave in Siberia, but that was not their usual abode. Instead, South-East Asia was their centre (see Figure 5.2). When conditions were good they expanded north, and when conditions were bad those populations died out or disappeared.
FIGURE 5.2 Denisovan fossils first turned up in Siberia, but these ancient humans probably arose in the Middle East before migrating north and south-east. Today their DNA is found mostly in people east of the Wallace Line.
That first finger-bone fragment has divulged a wealth of genetic information, but there are key questions it cannot address. For instance, were Denisovans relatively simple-minded like their H. heidelbergensis ancestors, or did they have the higher mental abilities of Neanderthals and early modern humans? DNA analysis cannot answer that, because we do not understand the genetic changes that made modern humans. But a skull with a big or small braincase would tell us. So the biggest challenge remains the same: to find a body.
The Neanderthal and Denisovan within
As soon as it became clear that so many modern humans carry Neanderthal and Denisovan DNA, the immediate question was: so what? Did the non-human DNA actually do anything, or was it effectively neutral – perhaps so similar to our own that its presence made no difference?
Recent genetic decoding suggests that it partly accounts for differences in our physical appearance and affects our health. Some of this ‘undead’ DNA even helped us survive in places for which we were otherwise ill equipped. Here are four examples:
1 High-altitude survival
Perhaps the most dramatic evidence of modern benefits from ancient DNA is seen in Tibetans, about 80 per cent of whom carry a particular piece of Denisovan DNA. The stretch of ancient DNA overlaps with the EPAS1 gene, the Denisovan version of which seems to help people survive the low-oxygen conditions at high elevations. It is possible that Denisovans were adapted to life at altitude and passed the trait to humans.
2 The gift of immunity
The first Homo sapiens to arrive in Europe and Asia would have encountered new parasites and pathogens, leaving them at risk from deadly diseases. Bumping into Neanderthals and Denisovans may have had very real advantages for these early explorers: modern Eurasians owe a significant portion of their immune system genes to these two ancient relatives.
Several studies have compared these genes in living humans with the versions in our extinct cousins and found remarkable similarities. In some populations in Papua New Guinea, for example, Neanderthal and Denisovan versions of the HLA-A immune system gene are nearly ubiquitous. Acquiring these genetic variants may have facilitated the health and survival of migrating bands of modern humans, when they were first exploring outside Africa.
3 Paler skin for northern skies
Neanderthal DNA may have contributed to the appearance of pale skins in some populations. Seventy per cent of people with European ancestry carry a segment of Neanderthal DNA on chromosome 9. This DNA spans a gene associated with pale skin pigmentation and freckling, and is absent in those with no European origins.
Of course, other factors could have contributed to the evolution of paler European skin colour. But if the Neanderthal DNA did play a role, it is easy to imagine how the trait might have been beneficial to early Europeans. Dark skin protects us from the harmful effects of UV radiation, but makes it harder to generate vitamin D at higher latitudes. Pale skin could have helped our species survive on less sunlight as it migrated north.
A similar genetic legacy remains in Asia: a chunk of Neanderthal DNA on chromosome 3 is found in about half the population. It overlaps with HYAL2, a gene involved in skin repair. Some studies show that HYAL2 responds to UV light exposure, which could suggest that the Neanderthal DNA helps repair skin damage from sunlight.
4 A tolerance of cold
One particular piece of Denisovan DNA found on chromosome 1 is present in nearly all indigenous Inuit Greenlanders. According to one study, the DNA contains two genes – TBX15 and WARS2 – and alters the way they are expressed in the body. TBX15 helps generate brown fat cells that produce heat in cold temperatures, and it is thought that both genes may influence body-fat distribution.
It is possible that modern humans acquired this DNA from a lineage that had adapted to cold conditions. When they began moving into the polar regions, individuals with the ancient DNA would have had a much greater chance of surviving and passing the genes on to their children.
The man rewriting human evolution: an interview with Svante Pääbo
Svante Pääbo is a Swedish biologist famous for his work on ancient genomes. One of the founders of paleogenetics, he has worked extensively on the Neanderthal genome. His DNA analysis of a finger bone found in the Denisova Cave in Siberia suggests that the bone belonged to a previously unrecognized member of the genus Homo: the Denisovans.
FIGURE 5.3 Svante Pääbo
Tell us about the discovery of the Denisovans.
We knew people had lived in this cave, but thought they were either Neanderthals or modern humans. When we sequenced the DNA I was in the US, so a postdoc called me to tell me the results. He said: ‘Are you sitting down?’ because it was immediately clear that this was some other form of human – not a Neanderthal, not a modern human. We were totally shocked.
Does the discovery of the Denisovans raise the possibility that we once shared the planet with other types of extinct human?
Yes; I wouldn’t say that’s impossible but I would still guess that there would be a limited number. At the time when modern humans came out of Africa, say 50,000 years ago, what was around? Well, we know there were Neanderthals and Denisovans, and we know there were ‘hobbits’, or Homo floresiensis, the short hominins discovered on the Indonesian island of Flores in 2003. So there were at least three forms. Maybe there were a couple more; it’s possible. We will know when we have studied more sites.
Do you ever wonder what the world would be like if Neanderthals had survived?
I think it’s a fascinating thing to think that, with just 2,000 more generations, Neanderthals would still be here with us. Would they live in suburbia or would they live in a zoo? How would we deal with them? Perhaps racism against Neanderthals would have been even worse than the racism we experience today, because they were truly different from us in some respects. Or would having another form of human around have allowed us to be more open-minded and not make this enormous distinction we make between humans and animals today? No one can know, but it’s interesting to speculate.
Meet the hobbits
There is one more Homo species to discuss. In 2003 the remains of a tiny and hitherto unknown species were discovered in Indonesia. The discovery was heralded as the most important for 50 years, and has radically altered the accepted picture of human evolution. Because the species was so small, they were quickly nicknamed ‘hobbits’ after the diminutive people in J. R. R. Tolkien’s novels The Hobbit and The Lord of the Rings.
The skull and bones of one adult female and fragments from up to six other specimens were found in the Liang Bua limestone caves on Flores Island, which lies at the eastern tip of Java. The female skeleton, known as LB1 – or by the nickname ‘Ebu’ – was assigned to a new species: Homo floresiensis. The skeleton shows a mixture of characteristics that until now have been associated with very different stages of human evolution.
One of the most striking characteristics of LB1 is her height. At around a metre tall, she is far shorter even than modern Pygmies, who range from 1.3 to 1.4 metres, and roughly the same size as the relatively primitive Australopithecus. But australopithecines, such as Lucy, lived in Africa between 1.4 and 4.5 million years ago, whereas LB1 lived between 74,000 and 95,000 years ago.
Indeed, the shape of LB1’s skull is more like that of our ancestor Homo erectus, which lived between 1.8 million and 200,000 years ago. That suggests that she, like H. sapiens, is a direct descendent of H. erectus. For instance, she has the protruding brow ridges typical of H. erectus.
Meanwhile, the body shape of H. floresiensis is in many ways more like the australopithecines than any human species. Her arms are so long that her hands reach almost to her knees. She has short legs with curved thighbones and a small pelvis.
But it’s the size of the skull that most shocked anthropologists. It could not have contained a brain any bigger than a grapefruit – similar in size to a small chimpanzee’s brain – which raises the conundrum of how such a minuscule brain was capable of the sophisticated behaviour suggested by the discovery of tools and animal remains nearby. The cut-off for the genus Homo used to be 500 cubic centimetres; yet H. floresiensis has a capacity of only 380 cubic centimetres.
A handful of stone tools from the same period were also found in the caves, along with the bones and teeth of several dwarf stegodons, an ancestor of the modern elephant. Other animal remains, including rats, bats and fish, show signs that they were cooked at around the time H. floresiensis inhabited the caves.
The natural question to ask is: when did the hobbits live, and when did they die out? When the species was first described, accelerator mass spectrometry dating suggested that LB1’s remains were 18,000 years old, and the scientists believed that some bone fragments could be as young as 13,000 years old. The oldest remains from the site were 78,000 and 94,000 years old.
Those dates would mean that H. floresiensis survived well beyond the last Neanderthals, and probably after the Denisovans, too. What’s more, Homo sapiens are thought to have colonized Flores island between 55,000 and 35,000 years ago, implying that the hobbits coexisted with us on the island for thousands of years.
That conclusion held for over a decade. But in 2016 it was demolished by a new dating study. This revealed that the skeletal remains were between 100,000 and 60,000 years old, and that the most recent stone tools were 50,000 years old. This implies that the hobbits disappeared around 50,000 years ago. That is a suspect date, because it is also around the time when modern humans arrived on Flores. It implies, but does not prove, that we may have – even if entirely inadvertently – pushed them to extinction.
What exactly is a hobbit?
The discovery of Homo floresiensis was so extraordinary – particularly coupled with the initial claims, since disproved, that it survived until 12,000 years ago – that some anthropologists did not believe it was a new species at all. Instead, they argued that the remains were those of a Homo sapiens with a disorder such as microcephaly.
The result was an almighty row that lasted for years. On one side was Robert Martin of the Field Museum of Natural History in Chicago, who argued that the existence of a species of small-brained dwarf human was a fantasy. Instead, he argued, the fossil is merely a Stone Age human with a mild form of microcephaly, a disease that stunts brain development and is associated with small stature. And he argued that the stone tools found at the site were made by regular Homo sapiens.
For many researchers, a 2005 analysis of the diminutive cranium confirmed that H. floresiensis was a unique species. It revealed remarkably advanced features for such a small brain. A 2007 study came to the same conclusion. It stated that hobbits had wrist bones almost identical to those found in early hominids and modern chimpanzees, and so must have diverged from the human lineage well before the origin of modern humans and Neanderthals.
Not everyone is convinced, but for most anthropologists H. floresiensis is genuine.
The origins of hobbits
Instead of Homo following a simple evolutionary path culminating in modern humans – Homo sapiens – the discovery of the hobbits suggested that early humans branched into many more forms than previously thought. This has been confirmed by the subsequent discoveries of the Denisovans and H. naledi.
But who were the hobbits’ ancestors? Two studies from 2009 outlined the possible answers. One idea is that hobbits evolved from a very early Homo species, something small like H. habilis. Alternatively, a group of later, larger H. erectus could have reached Flores about a million years ago, only to shrink because of peculiar conditions on the island.
Since island species, separated from their mainland kin, often decrease in size over evolutionary time, the ‘hobbit as separate species’ arguments have focused on its small brain. Lack of resources could select for smaller and smaller bodies, and some researchers have argued that power-hungry brains can shrink even more drastically than the rest of the body. Put simply, it might be advantageous for the animal not to have to maintain such a big brain. On that basis, some have argued that H. floresiensis was an insular dwarf of H. erectus.
However, others say that H. floresiensis cannot be a shrunken H. erectus. For a start, the feet of H. floresiensis are far longer than would be expected of 1-metre-tall H. erectus or H. sapiens. Instead, perhaps the hobbit’s closest relative is a species of human more ancient than H. erectus, with a smaller brain – perhaps H. habilis.
The story took a new twist in 2016: a new cache of hobbit-like remains had been uncovered on the island of Flores – six teeth, a fragment of jawbone and a tiny piece of skull. Their discoverers argued that they backed the shrunken H. erectus theory.
The fossils were collected in the So’a Basin on Flores, which was an African-like savannah at the time. They are 700,000 years old, much older than the original hobbit remains, suggesting that they are the ancestors of hobbits. The similarities with the hobbit are striking. In particular, the jawbone, which the team says belonged to an adult, is just as small as its hobbit equivalents. If the fossils are, in fact, older members of the hobbit lineage, then Flores seems to have been their home for hundreds of thousands of years.
Yet another idea came to the fore in 2017. The most comprehensive analysis yet suggested that the hobbits were, in fact, descended from a mystery ancestor that lived in Africa more than 2 million years ago. Some members of this ancestral group remained in Africa and evolved into H. habilis. The others moved out of Africa about 2 million years ago – before H. erectus did – and arrived in Flores at least 700,000 years ago.
Colin Groves at the Australian National University found that H. floresiensis was far more closely related to H. habilis than to H. erectus or H. sapiens, suggesting that it came from an ancient lineage and shared a common ancestor with H. habilis. Its more primitive, diminutive body type reinforces this idea. Groves argued that the hobbit’s ancestors probably died out across Asia when bigger, more complex human species like H. erectus and H. sapiens later emerged from Africa. H. floresiensis was probably able to cling on in Flores for as long as it did only because of its isolation. There is no fossil evidence to indicate that H. erectus ever made it to the island.
This debate looks set to run and run.
More species to come
It seems unlikely that we have discovered every hominin species that ever existed. In particular, evolutionary biologists have long predicted that new human species will start appearing in Asia as we begin to look at fossilized bones found there.
A distinctive skull was unearthed in 1979 in Longlin Cave, Guangxi Province, China, but it was only fully analysed for a 2012 study. It has thick bones, prominent brow ridges and a short, flat face, and it lacks a typically human chin. To sum up, it is anatomically unique. Darren Curnoe at the University of New South Wales in Sydney, Australia, who studied the skull, has argued that it presents an unusual mosaic of primitive features, like those seen in our ancestors hundreds of thousands of years ago, with some modern traits similar to those of living people.
Then Curnoe and Ji Xueping of Yunnan University, China, found more evidence of the new hominin at a second cave – Maludong in Yunnan Province. Curnoe has dubbed the new group the Red Deer Cave people because of their penchant for venison.
Exactly where the Red Deer Cave people belong in our family tree is unclear. They could be related to some of the earliest members of our species, Homo sapiens. However, they could also represent a new evolutionary line that evolved in East Asia in parallel with our species, just as Neanderthals did. It is also conceivable that they are the product of matings between modern humans and Denisovans. Although we do not know exactly where they came from, we do know that the Red Deer Cave people survived until relatively recently. Some of the fossils are just 11,500 years old.
In 2015 Curnoe published an analysis of a hominin femur, also found in Maludong. It shows evidence of having been burned in a fire that was used for cooking other meat, and has marks consistent with it being butchered for consumption. It has also been broken in a way that is often used to access the bone marrow. Someone seems to have cooked and eaten it.
Things got interesting when the team tried to identify the femur. The sediment in which the bone was found dated to just 14,000 years ago, but the femur resembles the earliest members of Homo. This suggests that remarkably primitive-looking humans shared the landscape with very modern-looking people – even at a time when China was developing early farming.
