The Origin of Our Species by Chris Stringer (2011)

This is a very demanding and scholarly book. In the last thirty years major leaps forward in DNA science, the technology of dating fossils, our ability to CT scan and analyse old bones and skulls right down to atomic level and other impressive techniques, as well as a steady stream of new finds of the remains of our prehistoric ancestors, have hugely deepened and complicated our knowledge of human ancestry, of the lineage which stretches back 6 million years to when our ancestors split from the ancestors of modern apes. It’s a massive, complicated and ever-changing field of knowledge.

As the blurb on the back points out, Chris Stringer has been closely involved in much of the crucial research into the origins of humankind and sets out in this book to explain all the latest research, techniques, discoveries and theories in the area, which he does comprehensively and thoroughly.

However, the patchiness of the evidence, the changing results given by evolving techniques, the legacy of sharply conflicting theories and interpretations etc, take a lot of explaining and putting into context. As well as the actual finds and the science we use to interpret them, the book slowly opens up a jungle of differences and debate between archaeologists, paleo-anthropologists, psychologists, DNA researchers, ancient historians and so on, at numerous levels, from large-scale over-arching theories to the interpretation of almost every single find and specimen.

Chapter by chapter, Stringer introduces us to all the evidence and all the techniques and all the controversies – but it is a lot to take in. It doesn’t help that the same theories, techniques and finds recur in different chapters, but in the context of different approaches or discussion of different theories or ideas. You need your wits about you. It’s a book to be read at least twice.

Two theories of human origins

In 1988 Stringer co-wrote an article titled Genetic and Fossil Evidence for the Origin of Modern Humans. This sketched out the two main theories about human origins: Recent African Origin (RAO) and Multiregional Evolution.

1. The multi-regional theory dates from the 1930s and believes that Homo erectus (himself descended from Homo habilis and a distinct species by about 2 million years ago) spread out from Africa over 1 million years ago, settling across Eurasia and Africa, and it was these scattered populations who all transitioned to modern man, Homo sapiens, although with variations which explain the different appearance of modern ‘races’.

2. Recent African Origin (also known as the ‘Out of Africa’ theory) agrees that Homo erectus spread across Eurasia by around 1 million years ago (the original or ‘Out of Africa 1’ scenario), but then postulates the separate development of ‘modern’ man (Homo sapiens) around 100,000 years ago, probably in East Africa. These modern humans also spread out beyond Africa (in so-called ‘Out of Africa 2’), superseding (overwhelming, conquering, killing?) their more primitive cousins wherever the two came into contact.

But a) there are numerous other theories which conflict with both the above, starting with an ‘Assimilationist’ theory, e.g. that Homo sapiens bred with Homo erectus rather than wiping them out; and b) almost every year brings new discoveries which throw up new puzzles and complicate the picture. Also c) Homo sapiens himself seems to have undergone a sudden burst of technological, cultural and social complexity around 50,000 years ago, when better tools, cave art, necklaces etc suddenly appear in the fossil record. It was this new, improved Homo sapiens who appears in Europe from 35,000 years ago. How does that fit into the timeline?

Neanderthal Man In Europe a distinct branch of humans was named Neanderthal Man (after the first specimen whose skull and bones were found in the Neander Valley in Germany in 1856). Neanderthal bodies were bigger, more muscly than ours, they had significantly larger brain cases (as Stringer humorously points out, in brains as with other things, size is not everything) but their most notable feature was really thick, heavy, threatening brow ridges over the eye sockets. Neanderthals are generally considered a distinct species, Homo neanderthalensis, and are thought to be descended from a more primitive species, Homo heidelbergensis, itself a branch of Homo erectus. Nenaderthal man became distinct from Heidelberg man around 600,000 years ago. (Typically, some paleoanthropologists disagree with the whole notion of defining these different specimens as distinct species, and consider Neanderthals and all the other ‘types’ which have been found in the past 150 years to be subspecies of Homo sapiens – thus Neanderthals would be Homo sapiens neanderthalensis).

One of the most intriguing questions remains what it was when I was a boy: We have evidence that modern man (often called Cro-Magnon Man in his European incarnation, after the cave in south-west France where the first specimen was found in 1868) and Neanderthal man both inhabited Europe at the same period, around 40,000 years ago (the Neanderthals having been around in Europe for hundreds of thousands of years, modern man being a new thing, fresh out of Africa). Shortly after the arrival of modern man, records of Neanderthals come to an end; there are no specimens more recent than 30,000 years ago.

So, did we wipe Neanderthals out? Archaeologist Nicolas Teyssandier has noted the period of overlap of the last Neanderthals and the first Moderns is characterised by a profusion of different types of spear tip – was there a stone age arms race? Or did ‘we’ interbreed with Neanderthals to become a cross-breed, Neanderthal records stopping because they had been ‘assimilated’ into our line – so that each of us has a little Neanderthal blood in us? Or did Neanderthals die out due to climate or other changes which they were too dim to adapt to, but which we with our super-smart brains managed to survive? The theories have become more intricate as new DNA evidence has emerged – but to this day, no-one knows.

Homo sapiens (left) Homo neanderthalensis (right)

Homo sapiens (left) Homo neanderthalensis (right)

Homo heidelbergensis This is another distinct form of human, that lived in Africa, Europe and western Asia between 600,000 and 200,000 years ago (and named after the first specimen, discovered in 1907 near the German town of Heidelberg). Some paleoanthropologists think that a population of heidelbergensis migrated into Europe and western Asia between 400,000 and 300,000 years ago and evolved into Neanderthal man. A later branch of the same family had evolved into Homo sapiens in Africa by around 130,000 years ago and then also spread into south-west Asia and Europe where, for 100,000 years, both related species lived alongside each other.

Periods

The Pleistocene period is said to date from 2.5 million years ago (Ma) to 12,000 years ago.

The Stone Age or Paleolithic period period lasted roughly 3.4 million years and ended between 8700 BC and 2000 BC, with the advent of metalworking (the date varying according to location, since different human groups developed metal work at different dates).

The Lower Paleolithic Period is 2,500,000 to 200,000 years ago. The Middle Paleolithic is the era during which the Neanderthals lived in Europe and the Near East, c. 300,000–28,000 years ago. The Upper Paleolithic dates from 50,000 to 10,000 years ago in Europe, ending with the end of the Pleistocene Era and onset of the Holocene Era at the end of the last ice age.

The Holocene Era is marked by the end of the ice ages around 13,000 years ago, followed swiftly (in the Fertile Crescent of modern Iraq) by the birth of agriculture, in what Jared Diamond calls ‘the Neolithic Revolution’. This saw humans transition from a life of hunting and gathering to one of agriculture and settlement, a transition whose causes and implicatoins Diamond deals with at length in his classic book, Guns, Germs and Steel.

Dating technologies

The modern technology used to date fossils and ancient remains is now bewilderingly complex and dauntingly sophisticated. Here are some terms; if you’re interested, you’ll have to google them for full accounts.

  • ABOX Acid Base Oxidation-Stepped Combustion pretreatment methods for dating charcoal thought to be over 30,000 years old
  • AMS accelerator mass spectrometry – a technique for measuring long-lived radionuclides that occur naturally in our environment
  • CT computerised tomography X-ray scan
  • ESR electronic spin resonance, method of dating
  • OSL – optically stimulated luminescence
  • TL thermoluminscence dating technique

New words and acronyms

I’m a humanities graduate, not a scientist; I get pleasure from new words and from new concepts (even ones I don’t fully understand).

  • Allen’s Law – animals in cold climates have low surface-to-volume ratios; animals in hot climates, the reverse.
  • atlatl – a spear thrower.
  • Biological Species Concept – the notion that species are defined as groups which can interbreed
  • burins – engraving tools.
  • CI Campanian Ignimbrite – debris from a huge volcanic explosion which took place in Campania, central Italy, 39,000 years ago.
  • Doggerland – the area of land that connected Britain to mainland Europe during and after the last Ice Age until it was flooded by rising sea levels around 6,500–6,200 BC.
  • Dunbar’s Number – after researching primate brain size against the size of their social groups British anthropologist Robin Dunbar estimated that humans can only form meaningful relationships with a maximum of 148 (generally rounded up to 150) other individuals.
  • EQ – encephalisation quotient, the ratio of brain volume to body mass.
  • glottology – the history or science of language.
  • Heinrich Event – brief but severe cold events when icebergs break off from northern ice caps and float south chilling the ocean and surrounding lands (pp.93-94)
  • microtephra – dust from a volcanic explosion which is invisible to the eye.
  • morphometrics – measuring shapes.
  • sapropels – dark layers of sediment laid down where the Nile reaches the Mediterranean.
  • survivorship – the proportion of a population surviving to a given age.
  • tang – edge or shoulder of a triangular stone point used to mount it as a projectile on a wooden handle.
  • varves – annually deposited layers in the bottom of deep lakes.

Snippets

  • Anthropologist Grover Krantz strapped on a fake thick protruding ‘brow ridge’ from a Homo erectus skull, and wore it for months (!) to see what advantages it brought. He discovered that it kept his hair out of his eyes, shielded his eyes from the sun – and scared the daylights out of people he met on dark nights. Stringer takes this last point seriously, saying the heavy brows of our ancestors possibly accentuated their stare, giving them an aggressive attitude which helped them intimidate other males and woo females, in the struggle for existence. (p.32)
  • Apparently, there are rumours in the paleoanthropology world that either the Americans or the Russians or both, in the 1940s and 50s, experimented by injecting human sperm into female chimps, bringing the resulting creatures to birth and experimenting on them. (p.33)
  • Male baboons gently fondle each other’s scrotums as a sign of friendship and trust – a defeated chimpanzee makes submissive noises and holds out its hand to the victor – if accepted the victor will embrace and kiss the supplicant, if rejected, he’ll bite it. (p.131)
  • Fire dates to around 1.6 million years ago in Africa, 800,000 years ago in Israel, 400,000 years ago in Britain. (p.140)
  • The Grandmother Hypothesis developed by James O’Connell and Kristen Hawkes proposes that human evolution favoured older women who lived on after the menopause (something which doesn’t happen in primates) who can help their daughters with child-rearing and food-gathering. (p.141)

Conclusion

The ninth and final chapter presents a conclusion of sorts – which is that, having extensively reviewed the current evidence, Stringer has modified his lifelong adherence to the Recent African Origin thesis in several ways:

  1. The one that surprised me the most has to do with the size of the communities we’re talking about. Up-to-date genetic evidence suggests that the groups which left Africa and moved out to populate Arabia and around the Indian coast, might have numbered in the hundreds. Even within Africa the various species may at any one time have only numbered in the thousands. (‘The long-term effective size of the ancestral population for modern humans might have been only about 10,000 breeding individuals’, p.175, whereas the number of breeding Neanderthal females in Europe might have been as little as 3,500). Given these numbers, the extinction of the Neanderthals is changed from being some kind of war of extermination (as it is sometimes painted) into the dwindling and going defunct of already tiny scattered communities (and the most attractive interpretation Stringer gives for this is the notion that Neanderthals were just bigger, heavier and needed more food than the lighter, nimbler Home sapiens – maybe in the unstable climatic situation in Europe 30,000 to 40,000 years ago, small and clever was simply more adaptable).
  2. The last two chapters bring together evidence which Stringer says can be interpreted, in light of these small numbers, to suggest a new hypothesis – that there were, at any given time, multiple human species living in Africa (he repeats several times that modern-day Africans show vastly more genetic diversity than any other continent – modern DNA evidence suggesting that the populations of Asia, the Far East, the Americas, Australia derive from very small bands of ancestors populations with the genetic diversity of modern populations dropping the further you go from the African source). In other words, the linear model of one species evolving into another species has been replaced by a much more complex scene of multiple species or sub-species flourishing in different places at different times. ‘100,000 years ago Africa may have comprised a collection of separate sub-groups’ (p.244). The evidence now suggests ‘that Africa contained archaic-looking people in some areas when, and even long after, the first modern-looking humans had appeared’ (p.255). In other words, the multiregion theory could be true within Africa, where multiple species, sub-species, varieties and groups of humans evolved along separate lines, developing widely different levels of tools, some isolated, some inter-breeding and leaving behind a patchwork of random relics to puzzle and confuse 21st century paleoanthropologists trying to create one continuous narrative.
  3. A recurrent problem in this new, more complex picture is that ‘superior’ technologies or skills seem sometimes, in some areas, to be replaced by inferior ones. Stringer uses the analogy of fires or beacons flaring up in the immense darkness of Africa for a millennium or so, then going out. Why? The brief answer, as with so much paleoanthropology, is that no-one knows. Climate change? Genetic drift? Drought, famine, conflict? But the stops and starts certainly fit with the newish idea of much greater diversity, variation, and contingency in our evolution than had previously been suspected.
  4. All of which brings Stringer to modify his initial RAO thesis: maybe there wasn’t one, but multiple out-of-Africa events. To me, as a layman, this doesn’t seem that surprising. Pre-human species didn’t have maps: they didn’t know they were ‘leaving’ Africa; they were just roaming, hunting and gathering wherever food could be found. It makes more sense to think there would have been multiple ‘exits’ from Africa. If our theories only posited two until recently, that could be because the archaeological record is so thin and patchy as not to spot the others – or it could be that numerous other ‘exit’ populations went extinct leaving no fossil or genetic trace. We think the exit event which led to us is important because it led to us; but it might have been just one among many, and its survival down to pure chance.
  5. And this leads to perhaps the most unsettling thought, which is all these theories tend to undermine our specialness. Even within scientific communities there has been a consensus that Homo sapiens is special because ‘we’ ended up inventing agriculture, cities, religion, states, navies, trains, rockets and all the rest of it – and therefore a tendency to try and identify the reason for that specialness and the moment when that specialness took hold. (Stringer thinks something happened around 50,000 years ago to change human behaviour, nudging it towards greater inventiveness – climate, size of social groups, who knows; but there are scores of other theories – he mentions the ‘Broad Spectrum Revolution’ theory proposed by Lewis Binford and Kent Flannery, a coming-together of climate, population size and innovation which they date to 20,000 years ago). But what if we’re not that special. What if Neanderthal man or some of the more obscure relics, such as Homo floriensis (the so-called ‘Hobbit’, a short version of modern humans found only in East Asia) or other sub-species and hominins as yet undiscovered, had just as much potential to develop and ‘succeed’ – but existed in such small populations that fairly limited events (drought, volcanic eruption, sudden chilling in an ice age) wiped them out and happened, just happened, to leave the field open to us? What if ‘we’ are only here by the merest luck or fluke but – with the arrogance typical of our species – have taken this as giving us an entirely spurious specialness, giving us the right to lord it over the earth and all the other species, when in fact our lucky ancestors just happened to be in the right place at the right time, or not to be in the wrong place at the wrong time…

Credit

The Origin of Our Species by Chris Stringer was published by Allen Lane in 2011. All quotes and references are to the 2012 Penguin paperback edition.

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