Outside of Africa, the archaeological site of Dmanisi in Georgia provides the earliest widely accepted evidence for the first major human dispersal, at around 1.8 million years ago.
The human species involved here is either Homo erectus, Homo ergaster or perhaps something new to science and not seen in the fossil records of Africa or East Asia.
Dmanisi has been a constant source of controversy in anthropology with views about its fossils ranging from a single to multiple species sampled at the site.
The oldest Homo erectus/ergaster fossils in East Africa have been found at Koobi Fora on the shores of Lake Turkana in Kenya, and these have dominated thinking about its evolution for 40 years.
Because of them, we’ve been locked into an ‘Out of Africa’ view about the species since the 1970s.
The most recent research on their geology and dating, however, suggests that all of the Koobi Fora remains except a single fossil are actually younger than those from Dmanisi.
Further east, the human fossils from Java, which also belong to Homo erectus, are dated between 1.6 million years and surprisingly as young as about 40,000 years old. I’ll leave the younger ones for another day.
More controversially, in China, stone tools from Longgupo Cave and Renzidong could be even older at between 2.0 and 2.5 million years old.
Less troublesome are the two teeth from Yuanmou in southwest China, which are believed also to belong to Homo erectus or a related species but date to around 1.7 million years old.
The big issue this all raises is that we simply can longer assume that Homo erectus evolved in Africa and dispersed into Asia. In fact, the evidence is building that it might actually be the other way around.
Enter India. Specifically, the Siwalik Hills north of the city of Chandigarh.
The ‘Siwaliks’ have been well known in palaeontological circles for over a hundred years, providing an abundance of fossils including some of the first evidence for extinct apes, going back to over 9.2 million years old.
New research by a joint Indian-French team has found new evidence about the first humans to settle Asia, and it’s bound to hit anthropology like a tsunami if the work stands up to scrutiny.
Near the village of Masol, archaeologists have found scatters of stone tools and animal fossils, some sporting cut marks by early humans while butchering carcasses, and all believed to date to about 2.6 million years old.
Until last year, this would have made them among the oldest stone tools anywhere in the world; though that honour now belongs to the Lomekwian tool industry from Kenya.
The discovery, published as a set of articles in the journal Comptes Renus Paevol, was led by scientists from various French institutions such as the Histoire naturelle de l’Homme préhistorique and the Society for Archaeological and Anthropological Research in Chandigarh.
Such an early age would push us back well beyond Homo erectus/ergaster and into the mysteries of the earliest members of Homo, about whom we still know so little.
So, Asia might have been settled by humans soon after the evolution of Homo; and such a primitive species could even have given rise to Homo erectus, perhaps in Asia itself.
The reaction to the discovery has been mixed, as you might expect, and some reasonable questions about the context of the finds have been asked.
All of the tools were found on the ground surface and none were recovered during excavations undertaken at a number of locations.
Still, the work makes it clear that they must have come from nearby, and very old, sediments.
And, we’d do well to remember that most of the fossil humans found at famous sites like Koobi Fora during the 1960s-1980s were also found on the surface.
When fossils and stone tools still have sediment attached to them, as the one’s from Masol do, it should be a relatively straight forward process to sort out where they eroded from.
The new discovery shows once again that we have for far too long focused too intensely on the archaeological record of Africa.
Asia still has many surprises awaiting us; and I’m sure a few more will be revealed in the year ahead.
Archaeological discoveries in East Asia over the last decade or so have dramatically rewritten our understanding of human evolution.
But the implications don’t sit easily with many scholars internationally who continue to see Europe and Africa as the heartland of human origins.
For more than 150 years our understanding of human evolution has been largely shaped by the discoveries made in Europe and parts of Africa, like the caves near Johannesburg and the Great Rift Valley on the east of the continent.
This is partly because disciplines like geology, evolutionary biology and archaeology, as we know them today, began in Europe during the 19th Century.
They set out to make a name for themselves, put their ‘new’ countries on the map, scientifically speaking, and turn the spotlight away from Europe, the centre of intellectual power.
East Asia featured prominently in the history and theory of human evolution during the late 19th Century and early 20th Century, but by the mid-1900s it was viewed internationally as an evolutionary backwater.
The first discovery to put Asia on the map was Pithecanthropus found by Eugene Dubois and his team in Java in 1891-92.
Then, the finding of Sinanthropus at Chou Kou Tien (now Zhoukoudian) near Beijing by Otto Zdansky from 1921, and soon after by Davidson Black and Li Jie, seemed to confirm its importance.
As an aside, among these early East Asian prehistorians, Dubois’ story stands out as the most fascinating, and his discovery of Pithecanthropus erectus (now Homo erectus) is one the most important in the history of archaeology.
Dubois was a young medically trained Dutch anatomist fascinated by 19th Century ideas about evolution, especially those developed by the highly influential German biologist Ernst Haeckel; Darwin’s continental intellectual rival.
Haeckel discovered and described hundreds of species, but was also the first biologist to draw an evolutionary tree or pedigree that included humans, placing us correctly among the Great Apes of Africa and Asia.
This was a profound moment in European science and it had a big impact on the archaeologists of the time.
To account for the evolutionary divergence of humans from the apes, Haeckel needed an intermediate step or ‘missing link’ for his tree, so he invented a speechless human-like ape, which he dubbed ‘Pithecanthropus’.
In 1887, Dubois left a plum job as an anatomist at the University of Utrecht, where he was on track to rapidly become a full professor, for a position as a military surgeon in the colonial army so he could find Pithecanthropus.
Remember, this was almost forty years before Dart discovered the Taung Child (Australopithecus) in South Africa, and 45 years before Louis Leakey made his first discovery in the East African Rift.
And find it he did, in just four short years. An incredible achievement.
Through the 20th Century, work continued, off and on, in archipelago Southeast Asia and on the mainland of East Asia, and was increasingly undertaken by local archaeologists.
But political events especially the rise of Communism meant that many East Asian countries and their scientists became isolated from the international community.
And as colonial powers pulled out of East Asia after World War II many nations had other priorities, with archaeology receiving less attention than it had under European rule.
From its first published description in 1913 until its eventual exposure as a fraud in 1953, the Piltdown skull played a major role in shaping ideas about human evolution, and was one of the main reasons why East Asia continued to be overlooked.
This was seemingly confirmed with the discovery in the 1970s and 1980s of Homo erectus remains that predated those from Asia, further marginalising the region.
With the wide acceptance of the so-called Out-of-Africa theory of modern human origins from the 1980s onwards, and concurrent gradual decline in acceptance of the alternatives (like the model Multiregional origins model), marked the final nail in the coffin for East Asia.
But then, the unexpected happened. The unearthing of a 15,000 year old pre-modern human on the island of Flores in eastern Indonesia.
The dramatic discovery of the Hobbit, or Homo floresiensis, a one metre tall human with a grapefruit sized brain, and in most respects resembling three million year old pre-humans like ‘Lucy’ from Africa, changed everything.
A new discovery published recently in Nature marks yet another find in the ever lengthening list of exciting and history altering discoveries.
Stone tools and animal fossils dated to between 100,000 and more than 200,000 years old have been found in Walanae Basin of Sulawesi: the oldest archaeology in the island, and showing it was inhabited by a unknown archaic species long before modern humans were on the scene.
Sadly, no human bones were found, so we have no idea who made the tools.
I suspect they were made by a species that we don’t see anywhere else. Not Homo erectus, nor Homo floresiensis, but a novel one. Why?
Sulawesi sits on the eastern edge of the famous biographic zone ‘Wallacea’ – marking the transition from an Asian ecology to an Australasian one – and has a truly remarkable fauna and flora.
It’s also located just to the north of Flores and so was probably on the North-South migration path for many animals including early humans.
The mammals that inhabit Sulawesi today are remarkable for their diversity: of the 127 endemic mammals that inhabit Indonesia, 62 percent are unique to Sulawesi.
In my view, the same kinds of evolutionary pressures that led to this remarkable diversity of non-human primates would have acted also on the early humans inhabiting the island.
A couple of hundred thousand years is plenty of time for new species to form.
Besides, we have the precedent of Homo floresiensis immediately to the south, and very like multiple species represented in the Homo erectus sample from nearby Java also.
It’s well and truly time to reassess the role East Asia played in human evolution, and to recognise that far from being a backwater, it was in fact a hotbed of human evolution right up till the end of the Ice Age.
This is because they fall squarely within my own area of research: human evolution over the past few hundred thousand years in East Asia and Australasia.
Unlike anything else
In 2012, we announced the discovery of the ‘Red Deer Cave people’ in Southwest China, a mysterious human group we identified from cranial and jaw bones and teeth from two cave sites located in Southwest China.
Today, a team I co-lead with Professor Ji Xueping of the Yunnan Institute of Cultural Relics and Archaeology, and involving colleagues from a range of institutions in China and Australia, announced the discovery of yet another highly unusual bone from the Red Deer Cave people. And it seems to confirm they were a mysterious group of pre-modern humans.
The Red Deer Cave (Maludong) during research in 2008. Ji Xueping & Darren Curnoe, Author provided
Our previous work showed that the features of their bones and teeth possess a remarkable number of similarities to archaic humans. This is despite them having lived only between about 14,000 and 11,000 years ago from radiocarbon dating of charcoal.
Their anatomy was nothing like we’d seen before in modern humans, whether they lived 200,000 or 200 years ago: they were truly unique and a real mystery to us and many of our colleagues.
We suggested they could represent either a very early modern human population, perhaps one that settled the region more than 100,000 years ago and became isolated. Or, they could be a late surviving archaic species, akin to a population of Neanderthals surviving in isolation until the end of the Ice Age in Southwest China.
Some of our colleagues also proposed at the time that they might be hybrids between modern humans and an unknown archaic species as an explanation for their peculiar traits.
We had focused our work on the skulls and teeth, representing four or five individuals, thinking they would offer the best insights into just who these mysterious people might be.
But, alas, we were left with considerable uncertainty. There was no clear answer about which species they might belong to or whether they could be hybrids. So back to work we went.
Archaic or hybrid?
A couple of months ago we published a new study of the Longlin or Laomaocao Cave specimen, which we had also placed in the Red Deer Cave people in 2012.
We’re now treating it as part of a separate group, distinct from the bones from Red Deer Cave, or Maludong, and one that we now think is indeed very likely to be a hybrid. And direct dating on human bone now confirms that the specimen is only 10,500 years old.
The Longlin Cave cranium. Darren Curnoe, Author provided
If we’re correct, then either there were archaic humans still around at that time in Southwest China who interbred with modern humans, or their hybrid features persisted longer after interbreeding occurred because of isolation and perhaps through the action of natural selection or genetic drift.
Our study published this week outlines detailed work on a thigh bone or femur from Maludong, located only 6km Southwest of the city of Mengzi, near the Northern Vietnam border.
Like the skull bones from the site, it is also dated to about 14,000 years old. But unlike them, it provides a much clearer indication of what at least some of the Red Deer Cave people bones might be.
Our work shows that the thigh bone strongly resembles very ancient species like early Homo erectus or Homo habilis, which lived around 1.5 million years ago or more in Africa.
Red Deer Cave people thigh bone compared with a modern human (not to scale). Darren Curnoe, Ji Xueping & Getty Images, Author provided
Like these pre-modern humans, the Maludong femur is very small. The shaft is narrow, with the outer layer of the shaft (or cortex) very thin, the walls of the shaft are reinforced (or buttressed) in areas of high strain, the femur neck is long, and the place of muscle attachment for the primary flexor muscle of the hip (the lesser trochanter) is very large and faces strongly backwards.
Surprisingly, we reconstructed its body mass to be about 50 kilograms, making the the individual very small by pre-modern and Ice Age human hunter-gatherer standards.
We need to be a bit careful though, as it is only one bone. Still, when seen in the context of the archaic looking skull bones and teeth from Maludong, our results are very compelling.
How is it that such an ancient looking species could have survived until so recently in Southwest China? Well, the environment and climate of Southwest China is unique owing to the tectonic uplift of the Qinghai-Tibetan Plateau.
Yunnan Province today has the greatest biodiversity of plants and animals in the whole of China. It is one of 20 floristic endemic centres as a result of its complex landscape of high mountains, deep valleys, rift lakes and large rivers.
The region around Maludong is also biogeographically on the northern edge of tropical Southeast Asia and many species found there today are very ancient indeed. The area is a biological refugium owing to its variable topography and tropical location.
The Maludong femur might therefore represent a relic, tropically adapted, archaic population that survived relatively late in this biogeographically complex, highly diverse and largely isolated region.
Now, we can’t deny that our work is controversial, with some our colleagues simply unable to accept the possibility that archaic looking bones could be so young, especially in East Asia.
Yet, when Homo floresiensis was found a decade ago the same kinds of comments were made. This species looks a lot like Australopithecus skeletons, like Lucy), that lived in Africa 3 or 4 million years ago. While not everyone has accepted the so-called “Hobbit” from Flores as a valid new species, most anthropologists and archaeologists have.
At a conference in Shanghai this week, which I attended, scientists from the Russian Academy of Science in Siberia presented evidence about the cave of Denisova in southern Siberia. Coincidentally, a new article by the same team on Denisovan DNA also come out this week in the Proceedings of the National Academy of Sciences of the USA.
It was a big surprise to me to learn that they have found rather similar kinds of things at Denisova Cave, except that the bones are 30,000-40,000 years older than at Maludong.
They’ve recovered evidence for multiple archaic species like the Neanderthals and Denisovans in the same cave layers as modern human dating to about 50,000 year ago. And in a slightly older unit in the cave they have found Neanderthal, Denisovan and possible Homo erectus bones, again together from a single layer.
Within this context, and the Hobbit from Indonesia, our finds don’t look so out of place after all.
The author and colleague Ji Xueping at a Palaeolithic cave in southern China. Ji Xueping & Darren Curnoe, Author provided
We need to also keep in mind that most of what we know about human evolution is based on the fossil records of Europe and some parts of Africa, like the East African Rift Valley, and caves in South Africa.
We’re quickly learning that Europe and Africa may not provide the best model for us to use to interpret the fossil record of East Asia. For example, Denisova Cave is as far east as we’ve found the Neanderthals, and they don’t seem to have occupied Siberia permanently. This is unlike Europe, where they lived until about 40,000 years ago. And so far, no Neanderthals have been found in China or anywhere further South of Denisova Cave.
The fact is that we’ve really only scratched the surface in East Asia. We still have an enormous amount to learn about which species were living there when the first modern humans arrived, and about how they interacted with the Palaeolithic ancestors of living East Asians.
Despite the progress we’re making about these and other ancient humans in Southwest China, we’re left with many riddles still about the Red Deer Cave people. Just who exactly were these mysterious Stone Age people? Why did they survive so late? Why are they found only in tropical Southwest China?
What did modern humans make of them? And how did they interact with them when they encountered them? Did they interbreed with them?
We hope to be able to answer more of these questions soon.
Extinction is, after all, the end of evolution, and the loss of one species can have unexpected spin-offs.
The disappearance of a single species changes the composition and functioning of an ecosystem, with its delicate balance between its constituent species and the physical environment, honed by thousands or millions of years of evolution.
But if it’s a critical – ‘keystone’ or ‘ecosystem engineer’ – species that disappears, the entire ecosystem can be profoundly changed or even collapse.
They destroy trees sometimes turning woodlands into grasslands, dig up huge amounts of soil in foraging and when drinking water and their dung can cover the ground in densities of up to 2 kg per square metre.
But, compared to humans, their impacts are significant only on local and regional scales, and globally unimportant.
Yet humans are clearly the greatest ecosystem engineer that has existed.
So widespread has the damage caused by us been, especially over the last couple of hundred years, that the planet itself may even have entered a ‘state-shift’ in which the biosphere may be close to a ‘tipping-point’.
Whole ecosystems are being transformed, many have collapsed, and all as a result of species loss and too little time and space for evolution to take its course, disallowing plants and animals to adapt to change.
Take plants: modelling suggests that for roughly 30 percent of the planet, the pace at which species will have to migrate just to keep pace with projected climate change is much greater than in the past when we saw major shifts during the Ice Age.
In many cases they’ll simply have nowhere to go as a result of human fragmentation of landscapes or because they occupy narrow zones like mountainous areas.
What might a state-shift in the planet’s biosphere look like?
Well, we can look to the past to get some idea of what might happen, only this time, more dramatic.
The last great cold phase of the Ice Age – dubbed the Last Glacial Maximum – occurred between roughly 30,000 and 15,000 years ago.
After this time the climate became punctuated by a number of short and rapid changes before entering the modern climate phase.
A short warming occurred between roughly 14,500 and 12,500 years ago, followed by another cold phase lasting about 1,000 years, until the present warm period called the Holocene began around 11,500 years ago.
With these swings from cold to warm to cold and back to warm there were dramatic changes in weather patterns at local and regional scales, and profound ecological shifts across the planet.
Rainfall and wind patterns, weather cycles, and humidity levels changed. Natural fire regimes altered.
There were major shifts in the distributions of plants and animals.
Many species were lost and ecosystems altered in composition, resulting in major shifts in biodiversity.
In short, the biosphere went through a turbulent time with around half of the planet’s species of large-bodied mammals going extinct, as well as a number of species of large birds and reptiles, and a few species of small animals.
We’ve no idea how many plant or insect species were lost.
This time also ushered in the development of agriculture or the Neolithic period.
This construction of a new human ecological niche through cultural and technological change was one of the most profound events in the evolution of modern humans; more profound even than the changes the ensued when our kind first left Africa 60,000 years ago.
Yet, it led to changes in the human genome associated with changed diet and disease exposure, within a few thousand years of agriculture commencing.
Agriculture saw large tracts of land being cleared, animals and plants domesticated, humans dramatically shifting their diets, big changes in the diseases suffered and their epidemiological patterns, many major migrations and population replacements, and people living a more sedentary life resulting in the beginnings of cities, states, extensive trade and warfare.
As adults, we’re often nostalgic for our childhood. A time when life seemed so much simpler. When we were free from the hassles of money, pressures of work and responsibilities of family and care.
When we were free to play and imagine people and worlds far from reality, and almost everything we did was new, exciting, and to be explored and understood; to be conquered, torn apart, feared, cuddled or tasted.
It might come as a surprise to learn that even having a childhood is something unique to humans.
We’re the only primate to have one, and the only one also to suffer the pangs of adolescence; but that’s another story.
Childhood is one stage in the human life cycle, or what biologists call our ‘life history’.
Life history is, for example, the time it takes for a fetus to grow, or the length of the various stages of life, like childhood or adulthood, important events like the age at first birth for a mother or the number offspring she has at each birth, age at death, and so on.
While every species has a unique life history, ours is downright weird compared to other primates, and indeed, most mammals.
Even among hunter-gatherers, our species normally lives around twice as long as our chimpanzee cousins do; we have the longest lifespan of all primates.
Infant mortality was similarly high among human foragers and chimpanzees, but if you survived until 15 years of age, your life expectancy would have soared to about 54 years (human forager) and 30 years (chimp) of age.
Most mammals including chimps have three stages in their life cycle: infancy, a juvenile stage and adulthood.
Infancy, the period from birth until weaning, when kids move onto solid food, is a lot shorter in humans though than other apes.
Infants in traditional societies were often weaned after about 3 years of age, but in chimpanzees it normally occurs around age 7.
Now, all primates except humans make the transition from infancy to adulthood via a juvenile (or ‘tween’) stage.
Instead, we pass through two extra stages in our life cycle – childhood and adolescence – giving us five stages of growth and development instead of three.
At each of these stages the body grows at different rates, different organs mature at varying times, and in traditional human societies, there were changes in the kinds of foods eaten and the roles kids played in society.
Childhood normally lasts around 4 years, from ages 3 until roughly 7 years of age. It’s the time after weaning when we would have been learning how eat solid foods, prepared for us by adults, when our brains reached their full size, and our first permanent molar teeth appeared.
Why are we the only primate to have a childhood? Well, it probably evolved as a mechanism to allow women to have more offspring.
Human females reproduce for around twice as long as chimps, owing to childhood and early weaning.
So, by weaning kids much sooner, mothers are free to reproduce again, and much, much, sooner than in other apes.
So our species can have many more children than any other apes through extending our overall period of reproduction and reducing the interval between births; which helps in part to explain why there’s seven billion of us today.
Intertwined with the evolution of childhood is the origins of grandmothering.
We’re also the only primate to experience menopause, or more correctly, to have grandmothers; women who live well beyond the reproductive stage of their lives.
Episode 12 of my UNSWTV series, ‘How did we get here’, looks at the importance of grandmothers in human evolution.
But human grandmothers probably evolved as a result of the early weaning of infants: weaned children rely heavily on foods collected and prepared by adults.
Hunter-gatherer children would also have been highly vulnerable to being killed by predators, and are especially vulnerable to disease. So, they would have, still do, demand considerable care and attention.
Because grandmothers have finished reproducing themselves, they are uniquely placed to invest time into helping feed and care for their grandchildren.
This would have greatly improved the survival of children, and allowed their daughters to have more of them, passing on more of their own genes through better survival rates among their grandkids.
And, not wanting to neglect the granddads entirely, the wisdom of a lifetime of experience for both grandparents must have been a great bonus for the entire community in handing down traditional knowledge, culture and understanding of the environment.
Hunter-gatherer fathers and grandfathers are also known to play a much larger role in childcare then other kinds of societies like pastoralists or farmers, and not just in providing food.
Perhaps men live to a ripe old age because evolution has favoured long lifespan for the entire species owing to the benefits of grandmothering? In this case, grandfathers might simply be incidental rather than a necessity.
Still, one pattern that seems to be consistent across many foraging societies is that an absence of grandmothers leads to higher childhood mortality than an absence of fathers.
When did childhood and grandmothering evolve? Its difficult to be certain because the different stages in human life cycle often don’t leave clear evidence for us in the fossil remains our ancestors.
The five stages in the human life cycle are universal and must therefore be under the strong influence of our genes. So its very likely that our unusual life cycle was present from the birth of our species as well.
Before 40,000 years ago old people were probably very rare in all communities, but their existence, especially of grandmothers, could have made a huge difference to child survival and mortality and may be the main reason we’re here at all.
The Conversation is fact-checking claims made on Q&A, broadcast Mondays on the ABC at 9:35pm. Thank you to everyone who sent us quotes for checking via Twitter using hashtags #FactCheck and #QandA, on Facebook or by email.
We, on average, for our entire history have associated with about 150 other people, and now after millions of years of doing that, we are a very social animal. – Professor of population studies at Stanford University, author and ecologist Paul Ehrlich, speaking on Q&A, November 2, 2015.
Professor Ehrlich’s assertion refers to a widely discussed figure known as “Dunbar’s number”.
The Dunbar (Robin Dunbar) number is ~150, size of hunter gatherer groups, still length of Christmas lists, and so on. My point was we’re a small-group social animal now suddenly (in cultural evolution time) trying to find ways to live in gigantic groups.
But does 150 really represent the ideal number of people we have all evolved to interact with socially?
The theory emerged from a series of studies beginning in 1992 by Robin Dunbar, a primatologist based at University College London. The studies aimed to understand the evolution of the large brain, especially the neocortex, of primates including humans.
The neocortex is the balloon-like, highly folded, outer part of the mammalian brain, which in humans is associated with higher cognitive functions like planning and executive control.
But let’s be clear up front: this number does not derive from an ecological principle or evolutionary law governing the way complex species like primates naturally organise themselves.
Instead, it is an estimate – a prediction – derived from an equation Dunbar used to describe the statistical association between neocortex size and the number of individuals typically living in the social groups of various primate species.
While his research has been widely cited and influential, especially in the social sciences and humanities, it has been very controversial. Indeed, it has been the subject of strong criticism in primatology and cognitive and experimental psychology.
So, what’s controversial about Dunbar’s number?
A bewildering array of correlations
First of all, it’s now well understood that larger sized mammals possess a larger neocortex: it comprises about 87% of a sperm whale’s brain, 80% of the human brain, 71% of a camel’s brain but only 15% of a shrew’s.
While we could speculate about the previously unappreciated intelligence of some of these species, there’s probably nothing particularly special about a large-bodied species possessing a large neocortex as such. A big neocortex may not necessarily tell us anything about that animal’s social life.
Second, other ecological factors have been found to produce similarly strong correlations with brain or neocortex size in primates.
Various studies have shown that other factors can explain neocortex size equally as well as social group size. They include primate territory size, diet (especially fruit-eating and other kinds of extractive feeding behaviour), and other variables like nighttime versus daytime activity patterns.
In fact, so many strong statistical correlations have been found by researchers looking into this question that one study bleakly noted the “bewildering array of correlations between brain size and behavioural traits”.
All of this points to the fact that Dunbar’s theory is regarded by many experts as an incomplete explanation for the complexity of primate brains, cognition and behaviour.
One common factor among many of these aspects of primate ecology is that they all rely heavily on visual cues and the processing of visual information by the brain.
The larger neocortex of primates results to a considerable extent from a larger visual cortex (visual brain system), which clearly has many demands on it. Social behaviour is just one of them.
Primates seem to be unique among mammals in showing a strong evolutionary link between an enlarging neocortex and a larger cerebellum, the brain region beneath the neocortex that processes and coordinates sensory and motor control and is involved in the learning of motor skills.
Focusing solely on the neocortex misses a big part of the picture of primate brain evolution.
Our human-centric view of the world
Another problem pointed out by other primatologists is that no matter how dispassionately we might study primate cognition, we will inevitably impose our own, species-centric view of the world on it.
This is the problem of anthropocentrism: our belief that humans are the most important species on the planet. We simply can’t escape making inferences through our own “socio-cognitive spectacles”, as pointed out by the philosopher Wittgenstein.
This problem becomes particularly acute with primates, which are our evolutionary cousins. It is easy for us to impose complexity on behaviours that may not be complex at all within primate (versus human) social settings.
Furthermore, when Dunbar’s number has been tested against the actual social organisation of historical and living hunter-gatherer groups, it has been found to be wanting.
The anthropologist Frank Marlowe, for example, has suggested that hunter-gatherers spend most of their time living in “local bands”, and that these typically comprise only around 30 people, regardless of where in the world they are living.
Dunbar, in responding to Marlowe, has pointed out that local bands are often unstable, and change in size regularly, making other (larger) units of social organisation more appropriate for investigation.
There is simply no agreement among researchers about which unit of human social organisation is the most appropriate one for studying evolution.
Many other criticisms have been levelled at Dunbar’s theory and show that it, and the predictions emerging from it about human social organisation, are widely regarded as overly simplistic.
While Professor Ehrlich correctly quoted the number 150 as Dunbar’s number, he didn’t quite present the whole picture. He could have been more accurate by linking the figure to its source and he overlooked the abundance of contradictory and highly critical published studies of Dunbar’s theory. – Darren Curnoe
The author has provided a good, critical assessment of Dunbar’s number and a useful discussion on the weaknesses of correlative comparative studies.
Dunbar’s number is an arresting idea with a pithy name, easy to digest and just counter-intuitive enough to have broad appeal, which may explain why the idea it encapsulates has caught on so readily outside of primatology and anthropology.
Despite the limitations and problems with Dunbar’s number and the idea that neocortex size seems adapted to living in social groups of fewer than 150 individuals, I believe Dunbar’s thinking remains useful.
In particular, I see value in Dunbar’s argument that at each level of closeness, we are limited in how many relationships we can have: an average of five intimate supportive relationships, 15 close friends and so on.
Whatever the neurobiological mechanisms, Dunbar has made useful predictions about the limited nature of human social capacity, and they remain to be thoroughly tested against competing ideas.
Paul Ehrlich quoted a piece of science that has become pop folklore, but that is also controversial.
However, the point he was making – that humans have limited social capacity and that our evolved social capacities don’t suit us well to living in societies of millions – has not been refuted.
I suggest that readers interested in this topic listen to Dunbar’s TED talk, especially the bit from about 7:20 in which he discusses the layered capacities for different types of relationship. – Rob Brooks
Can there be any more important a question than, ‘How did we get here?’
Of course, I don’t mean those books we all gawked at as tweens desperate to understand our transforming pubescent bodies.
I mean, ‘How did we get here, as a species?’ ‘How did we come to be so different to all other life?’
In the way that we look: with our large, balloon like brains and skulls, hairless bodies, tiny teeth, protruding chins, puny muscles, and bobbling about on two feet.
Also in the ways that we behave: with our remarkably complex and conscious brains, articulate speech and language, symbolic, creative, minds, and extraordinary imagination.
And how did we come to occupy virtually every nook and cranny the planet has to offer, even travelling to places beyond Earth?
The fossil, genetic and archaeological records provide the only hard evidence we have about our evolutionary past.
Yet, even if we cast our attention back to the Palaeolithic (or Stone Age) we really get no sense at all that we as a species would be destined to be the apes that would eventually shape the planet itself, on a global scale.
But each year, with the rapid pace of scientific discovery about our evolutionary past, our ‘biological patch’ is getting smaller and smaller; and, 2015 has been a truly remarkable year in this sense.
It seems like a good time to pause and take stock: How different are we? And, what can the records of our evolutionary history tell us about the journey to human uniqueness?
Our evolutionary branch on the tree of life began a mere 8 million years ago: a time when we shared a common ancestor with living chimpanzees.
Homo sapiens, also called ‘modern humans’ by anthropologists – a concept I’ll return to later – evolved according to the fossil record more than 200,000 years ago.
That’s a long time ago in terms of human generations of course: roughly 10,000 generations back.
But its a mere blink of an eye in the history of planet Earth and life.
In broad terms, we can divide the human evolutionary story into two major phases, and in doing so, can trace the gradual assembling of different parts of the ‘package’ of human modernity.
In the first phase, between roughly 7.5 million and 2 million years ago, we see a group of very ape like creatures living only in Africa.
Remarkably also, the earliest stone tools now date back to almost 3.5 million years ago: being invented by Lucy’s kind with their small brains.
Some archaeologists also think that some of the earliest members of Homo – notably Homo erectus – with its human body size, but brain three quarters the size of ours, may have been able to make and control fire.
The importance of fire is that it would have allowed our Palaeolithic ancestors to cook their food, unlocking new and sometimes safer sources of nutrition to feed an energy hungry and evolving brain.
But the oldest examples of fire are only around 300,000-400,000 years old, in the form of burnt bone and deep ash and charcoal layers in caves.
They are associated with the species Homo heidelbergensis or perhaps the earliest Neanderthals (Homo neanderthalensis) living in Europe and West Asia.
Still, it certainly predates Homo sapiens, showing that fire is far from being unique to us, as Charles Darwin once opined.
This evolutionary time also marked the very first excursions by a two footed ape out of Africa, with Homo erectus settling Europe and eventually Asia as far east as present day China and Indonesia beginning from at least 1.8 million years ago.
Around a million years later the species Homo heidelbergensis appears in the fossil record, and also has a rather wide distribution across Africa, Europe and Asia.
Homo heidelbergensis is likely to have been the species that gave rise to both our Neanderthal cousins and we modern humans, and like us, it occupied a very wide range of environments, with a few important exceptions.
Now, one of the most exciting human fossil sites ever found is Sima de Los Hueseos – ‘the pit of bones’ – in Atapuerca, northern Spain.
Here, anthropologists have so far found more than six and half thousand fossils of an early human species, dated to more than 500,000 years ago.
The bones are pilled up one atop another in a way that strongly suggests they were deliberately disposed of in the cave, as complete bodies: in a kind of human rubbish pit.
But, some of the scientists working at the ‘pit of bones’ think the piles of fossils represent not just intentional disposal of the dead but indicate a sense of the afterlife, representing a kind of burial practice.
Again, hundreds of thousands of years before Homo sapiens appears.
We also now know from DNA extracted from the fossils from Sima de Los Huesos that the bones sample an early part of the Neanderthal evolutionary branch.
This means that Neanderthals were disposing of their dead, but not necessarily burying them like we do, at least half a million years ago.
In tracing the origins of this (admittedly incomplete) list of features historically claimed to be unique to Homo sapiens we get the distinct impression that the ‘biological patch’ we humans have recognised as our own is narrowing rather quickly.
If many of the hallmarks of humankind can no longer be claimed as exclusive, what does this leave for our species to claim as unique, and to explain the differences between us and other life?
Not much, actually.
Anthropologists often use the term ‘modern humans’, more specifically, ‘anatomically modern humans’, more or less interchangeably with the species name Homo sapiens.
What’s meant by this term is essentially any fossil that would blend within the range of physical variation we see around the planet today, or in the recent past.
A related concept is that of ‘behaviourally modern humans’, which is used by archaeologists to distinguish humans whose behaviour we would recognise as being like our own.
Now, you might think this latter term would be unnecessary: surely, you might ask, anatomically and behaviourally modern humans are the same thing, right?
If only it were that simple!
Actually, the fossil record shows that the earliest bones that resemble living humans are from Africa, specifically, Tanzania, Ethiopia and South Africa, and are dated between about 220,000 and 170,000 years ago.
Why are they regarded to be anatomically modern human? Mostly on account of their bubble shaped skulls, large brain volumes, small teeth, and finely built jaws with protruding chins.
Anatomically modern humans got into West Asia, specifically present day Israel, more than 100,000 years ago.
But, until very recently, it was thought they didn’t get anywhere east or north of the Levant until much later, perhaps only 50,000 years ago, at most.
Skeletal remains dating to around 40,000 years old have been found at Lake Mungo in Australia, Niah Cave in Malaysian Borneo, Tam Pa Ling in Laos, and Tianyuan Cave near Beijing in China.
Just three weeks ago we learned that anatomically modern humans have been in East Asia, specifically southern China, for at least 80,000 years, and perhaps even 120,000 years.
Forty-seven human teeth from the site of Daoxian Cave, which are remarkably modern looking, provide a strong case for the precociously early occupation of the region by our kind.
When do we see the earliest evidence for behaviourally modern humans?
Stone tools don’t give us any real insights into this question for the first 100,000 years or so of our evolution as species.
That’s right, there is a gap of more than 100,000 years between the appearance of anatomically modern and behaviourally modern humans. Odd right?
The ‘smoking gun’ that archaeologists look for when trying to pinpoint the emergence of the modern human mind is the signs of symbolic behavior.
When we think about symbols we know that among living species we humans are the only ones, as far as we know, that are capable of inventing them.
A good example of a simple yet powerful symbol is the cross, as explored in my an episode of my UNSWTV series, ‘How did we get here?’
How might we get at this kind of thinking, of a symbolic human mind, from the archaeological record?
Archaeologists point to examples like the:
• Making of jewellery, with shell beads at least 100,000 years old in Africa.
• Grinding up of ochre to make paint for painting living bodies or of the deceased in preparing them during a burial ceremony.
• Cremation of the dead, with the earliest evidence being from Australia in form of the Mungo Lady who was cremated more than 40,000 years ago.
• Rock paintings on cave walls, the oldest, as of last year, being found in Indonesia and dating to about 40,000 years old, older than anything in Europe or Africa.
We modern humans also live in places other human species simply haven’t been found.
There’s clear evidence, especially from the archaeological record, that only modern humans have occupied deserts, rainforests, the Arctic Circle and even the Steppe Grassland environments seen in Siberia and Eastern Europe.
While we’re remarkably flexible and able to alter our diet, behavior and technology to suit our circumstances, this all occurred well after 100,000 years ago.
Why then did it seemingly take more than 100,000 years after our appearance as a species for the first signs of the modern human mind to make a show?
One possibility is that some kind of revolution occurred around this time – perhaps the arrival of complex human language being associated with a gene mutation.
One candidate is the FOXP2 gene, which is vital for the development of normal speech and language.
This gene is shared with Neanderthals and chimpanzees as well, but we humans have a particular mutation affecting the regulation of the gene that is not found in the genome of our cousins.
Ironically, as we gather more scientific evidence, and our technologies get more powerful, the big questions about our past, evolution and place in nature get harder to answer with any satisfaction.
With only around 100 genes of any consequence distinguishing us from our Neanderthal cousins, and most of them being related to our immune system, skin or sense of smell, we are being forced to focus now on the small biological changes in our evolution to explain what feels like a massive gulf.
Seemingly changes of only minor genetic importance had profound consequences for us as a species, and, as it turns out, the well being and future of the planet as well.