To the memory of lost family Tony and David, and lost colleagues Bill, Clark, and Roger
Contents
Title Page
Dedication
List of Illustrations
Introduction
1. The Big Questions
2. Unlocking the Past
3. What Lies Beneath
4. Finding the Way Forward
5. Behaving in a Modern Way: Mind Reading and Symbols
6. Behaving in a Modern Way: Technology and Lifeways
7. Genes and DNA
8. Making a Modern Human
9. The Past and Future Evolution of Our Species
Sources and Suggested Reading
Acknowledgments
Index
About the Author
Also by Chris Stringer
Copyright
Illustrations
Copyright information is given in parentheses
Eugène Dubois and his “Pithecanthropus erectus” skull (John Reader)
Map showing early human sites (Chris Stringer)
Replica of the Heidelberg jaw (The Boxgrove Project)
Franz Weidenreich and some of the “Peking Man” fossils (John Reader)
Louis Leakey with the Olduvai Gorge “Zinjanthropus” skull (Natural History Museum, London)
Chris Stringer on his 1971 research trip around Europe (Chris Stringer/Rosemary Lee)
Milford Wolpoff (David Hart)
Günter Bräuer and Chris Stringer (Günter Bräuer/Chris Stringer)
Skulls of erectus, heidelbergensis, sapiens, and neanderthalensis (Natural History Museum, London)
Side view of skulls of erectus, heidelbergensis, sapiens, and neanderthalensis (Natural History Museum, London)
Ranges of the main dating methods for recent human evolution (Chris Stringer)
Boxgrove handaxes (The Boxgrove Project)
Skeleton from the Neander Valley (John Reader)
Skulls from Jebel Irhoud and La Ferrassie (Chris Stringer/Musée de l’Homme, Paris)
The Oase fossils (Erik Trinkaus)
Oblique view of the Herto skull (courtesy and © Tim White)
Side view of the Herto skull (courtesy and © Tim White)
The child’s skull from Herto (courtesy and © Tim White)
Map showing early human sites in Europe (Chris Stringer)
Objects from Hohle Fels Cave, Germany: “Lion Man” (Juraj Lipták/University of Tübingen); flute (Hilde Jensen/ University of Tübingen); Venus (Hilde Jensen/University of Tübingen); waterbird (Juraj Lipták/University of Tübingen)
Excavations outside Vogelherd Cave, Germany (Maria Malina/ University of Tübingen)
Blombos Cave, South Africa, exterior (Chris Henshilwood)
Blombos Cave, South Africa, interior (Chris Henshilwood)
Still Bay tools from Blombos Cave (Chris Henshilwood)
Ocher plaque from Blombos Cave (Francesco d’Errico)
Bone tools from Blombos Cave (Chris Henshilwood)
Tick shells from Blombos Cave (Chris Henshilwood)
Reindeer carving from Montastruc rock shelter, France (replica, Chris Stringer)
Pigments from Pech-de-l’Azé, France (Francesco d’Errico and Marie Soressi)
The mtDNA tree (Mark Stoneking)
Map showing the spread of early modern groups (Chris Stringer)
Chimpanzees cracking palm oil nuts (Susan Carvalho)
Diagram showing limited cultural transmission in archaic humans (Chris Stringer)
Diagram showing much wider cultural transmission in modern humans (Chris Stringer)
Map showing later human sites (Chris Stringer)
Map showing later human sites in Europe (Chris Stringer)
Mungo 3, Australia (Colin Groves)
Omo Kibish 1 and 2 (Michael Day)
Ngaloba skull (Chris Stringer)
Iwo Eleru skull (Natural History Museum, London)
Which model is “right”? (Chris Stringer)
Evolutionary tree (Chris Stringer)
Introduction
We have just celebrated the 150th anniversary of the publication of Charles Darwin’s On the Origin of Species and his two hundredth birthday, and evolution by natural selection is now widely accepted. But what do we know about the origin of our own species, Homo sapiens? Despite the fascinating and growing record of very ancient prehuman fossils, one topic has dominated recent scientific and popular discussion about evolution: our own origins. While it is generally agreed that Africa was the homeland of our earliest human ancestors, a fierce debate continues about whether it was also the ultimate place of origin of our own species, and of everything that we consider typical of our species, such as language, art, and complex technology. Originally centered on the fossil record, the debate has grown to encompass archaeological and genetic data, and the latter have become increasingly significant, now even including DNA from Neanderthal fossils. Yet much of these new data and the discussions surrounding them are buried in highly technical presentations, scattered in specialist journals and books, so it is difficult for a general readership, however informed, to get an accessible overview.
In this book I want to try and provide a comprehensive—but comprehensible—account of the origin of our species from my position in these debates over the last thirty years or so. I’ve worked at the Natural History Museum in London even longer than that, and the idea that I could have ended up there, studying our origins, was a boyhood dream which I never thought would actually come to pass, given my relatively humble origins in the cockney area of east London. But with supportive parents and foster parents and some teachers who encouraged me along the way, I started to realize that dream when, at age eighteen, I made a last-minute switch from studying medicine to taking a degree in anthropology. It was a gamble that paid off when I was accepted into the Ph.D. program at Bristol University in 1970 to study my favorite fossil people—the Neanderthals—and then even that was capped by the offer of a job in the Palaeontology Department at the Natural History Museum in London, in 1973.
It has been such an exciting time to be working in this field, with wonderful new fossil finds, but also the arrival of a host of new techniques to date and study them. I hope my book will make every reader think about what it means to be human, and change his or her perceptions about our origins—writing it has certainly changed some of mine!
I regularly give talks on human evolution and receive hundreds of inquiries on this topic every year from the media and the public. The same questions recur time and again, and in this book I will try to answer them. These questions include:
1. What are the big questions in the debate about our origins?
2. How can we define modern humans, and how can we recognize our beginnings in the fossil and archaeological record?
3. How can we accurately date fossils, including ones beyond the range of radiocarbon dating?
4. What do the genetic data really tell us about our origins, and were our origins solely in Africa?
5. Are modern humans a distinct species from ancient people such as the Neanderthals?
6. How can we recognize modern humans behaviorally, and were traits such as complex language and art unique to modern humans?
7. What contact did our ancestors have with people like the Neanderthals, and were we the cause of their extinction?
8. Do archaic features in modern human fossils and genes outside Africa indicate hybridization?
9. What does DNA tell us about the Neanderthals and possible interbreeding with modern humans?
10. What can we learn from a complete Neanderthal genome, and will we ever clone a Neanderthal?
11. What forces shaped the origins of modern humans—were they climatic, dietary, social, or
even volcanic?
12. What drove the dispersals of modern humans from Africa, and how did our species spread over the globe?
13. How did regional (“racial”) features evolve, and how significant are they?
14. What was the “Hobbit” of the island of Flores, and how was it related to us?
15. Has human evolution stopped, or are we still evolving?
16. What can we expect from future research on our origins?
It is now over twenty years since the publication of the seminal Nature paper “Mitochondrial DNA and Human Evolution” by Rebecca Cann, Mark Stoneking, and Allan Wilson that put modern human origins and “Mitochondrial Eve” on the front pages of newspapers and journals all over the world for the first time. Not only did that paper focus attention on the evolution of our own species, but it also led to a fundamental reformulation of scientific arguments about the way that we look at our own origins. A year after that publication, I wrote the paper “Genetic and Fossil Evidence for the Origin of Modern Humans” for the journal Science with my colleague Peter Andrews, which set out the contrasting models of modern human origins that have dominated debate ever since: the Recent African Origin model and the Multiregional Evolution model. Later in the book we will see how these models have fared in the face of many new discoveries, but in the first chapter I will look at some of the big questions of modern human origins, including what diagnoses our species, what the recent debates are all about, and how the different models lay out expectations of what we should find in the record of modern human evolution, from fossils, archaeology, and genetics.
1
The Big Questions
It is barely 150 years since Charles Darwin and Alfred Russel Wallace presented their ideas on evolution to the world. A year later, in 1859, Darwin was to publish one of the most famous of all books, On the Origin of Species. Then, the first fossil human finds were only beginning to be recognized, and paleontology and archaeology were still in their infancy. Now, there is a rich and ever-growing record from Africa, Asia, and Europe, and I have been privileged to work in one of the most exciting eras for discoveries about our origins. There have been highly significant fossil finds, of course, but there have also been remarkable scientific breakthroughs in the amount of information we can extract from those finds. In this first chapter I will outline the evidence that has been used to reconstruct where our species originated, and the very different views that have developed, including my own. There are in fact two origins for modern human features that we need to consider. Here, I will talk about our species in terms of the physical features we humans share today, for example, a slender skeleton compared to our more robust predecessors, a higher and rounder braincase, smaller brow ridges, and a prominent chin. But there are also the characteristics that distinguish different geographic populations today—the regional or “racial” characteristics, such as the more projecting nose of many Europeans, or the flatter face of most Orientals. I will discuss their quite different origins later in the book.
In The Descent of Man (1871), Darwin suggested that Africa was the most likely evolutionary homeland for humans because it was the continent where our closest relatives, the African apes, could be found today. However, it was to be many years before the fossil evidence that was ultimately to prove him right began to be discovered. Before then, Europe with the Neanderthals, “Heidelberg Man,” and the spurious “Piltdown Man,” and Asia with “Java Man,” were the foci of scientific attention concerning human ancestry. But the 1921 discovery of the Broken Hill skull in what is now Zambia, and the 1924 discovery of the Taung skull (from South Africa), started the process that gave Africa its paramount importance in the story of human evolution, even if that process still had many years to run. By the 1970s a succession of fossils had established that Africa not only was the place of origin for the human line (that is, the continent in which the last common ancestor of humans and chimpanzees lived) but was probably also where the genus Homo (humans) had originated. But where did our own species, Homo sapiens (modern humans), originate? This was still unclear in the 1970s and remained so until quite recently.
When Charles Darwin wrote in the Origin of Species, “light would be thrown on the origin of man and his history,” he was reluctant to say any more on the subject, as he admitted twelve years later in the introduction to The Descent of Man: “During many years I collected notes on the origin or descent of man, without any intention of publishing on the subject, but rather with the determination not to publish, as I thought that I should thus only add to the prejudices against my views.” But in the intervening years he had been fortified by a growing number of influential supporters and thus felt ready—finally—to tackle the controversial topic of human origins. He then went on to say: “The sole object of this work is to consider, firstly, whether man, like every other species, is descended from some pre-existing form; secondly, the manner of his development; and thirdly, the value of the differences between the so-called races of man.” However, Darwin acknowledged that there were still many doubters, something that unfortunately remains as true today as it was then: “It has often and confidently been asserted, that man’s origin can never be known: but ignorance more frequently begets confidence than does knowledge: it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science.”
Darwin then proceeded to pay tribute to a number of other scientists for their work on human origins, particularly the German biologist Ernst Haeckel, and this is especially interesting as Haeckel differed from him and Thomas Huxley (“Darwin’s bulldog”) over a critical question about our origins, a question that continues to be debated even today. In The Descent of Man Darwin wrote: “We are naturally led to enquire, where was the birthplace of man at that stage of descent when our progenitors diverged from the catarrhine stock [the catarrhines group includes apes and monkeys]?… In each great region of the world the living mammals are closely related to the extinct species of the same region. It is therefore probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man’s nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere.” However, he then proceeded to caution, “But it is useless to speculate on this subject … as there has been ample time for migration on the largest scale.”
Not only did Darwin have to deal with a dearth of fossil evidence in 1871, including a complete absence of any humanlike fossils from Africa, but there was also no knowledge of the concept of continental drift (the idea that landmasses migrated in the past, splitting and realigning as they moved across the Earth’s surface). This process is now known to underlie many of the present distributions of plants and animals (for example, the unique assemblages of species found in places like Australia and New Zealand). Previously, to explain puzzling links between species in different regions, now-sunken continents were often postulated. For example, lemurs are rather primitive primates that today are found only on the island of Madagascar, some three hundred miles off the coast of Africa, but ancient lemurlike fossils had been found in the Indian subcontinent, and such similarities led the British zoologist Philip Sclater to hypothesize in 1864 that there was once a large continent, which he named Lemuria, stretching across much of what is now the Indian Ocean.
Using the concept of this lost continent, Haeckel argued for a different ancestral homeland for humans: “There are a number of circumstances which suggest that the primeval home of man was a continent now sunk below the surface of the Indian Ocean, which extended along the south of Asia … towards the east; towards the west as far as Madagascar and the southeastern shores of Africa. By assuming this Lemuria to have been man’s primeval home, we greatly facilitate the explanation of the geographical distribution of the human species by migration.” Moreover, Haeckel differed from Darwin and Huxley in favoring the gibbon and orangutan o
f southeast Asia as better ape models for human ancestry than the gorilla and chimpanzee of Africa. And whereas Darwin followed the geologist Charles Lyell in arguing that the fossil record of human evolution was still unknown because the right regions had not yet been searched (in particular Africa), Haeckel preferred the explanation that most of the critical evidence was now sunk beneath the Indian Ocean.
Eugène Dubois and his “Pithecanthropus erectus” skull.
During Darwin’s lifetime, the Neanderthals were already known from their fossil remains as ancient inhabitants of Europe. While some scientists pushed them into the position of “missing links,” reconstructing them with bent knees and grasping big toes, others like Huxley recognized them as big-brained, upright, and unmistakably human. Darwin never lived to see the first discovery of a really primitive human fossil, announced by a Dutch doctor, Eugène Dubois, in 1891. Dubois had been inspired by Haeckel’s writings to get an army posting to what was then the Dutch East Indies (now Indonesia), to search for ancient remains. Haeckel had created the name “Pithecanthropus alalus” (“Ape Man without Speech”) for a hypothetical link between apes and humans that he believed had once lived in Lemuria. Dubois was blessed with luck in his excavations on the island of Java and soon found a fossilized and apelike skullcap and a human-looking thighbone. He named these “Pithecanthropus” (in honor of Haeckel) “erectus” (because the femur indicated this creature walked upright, as we do). We now know this species as Homo erectus, a wide-ranging and long-lived species of early human. But because this first find of the species was made on the Indonesian island of Java, it tended to reinforce Haeckel’s and Dubois’s notions of a Lemurian/southern Asian origin for humans, rather than an African one.
In naming “Pithecanthropus erectus,” Dubois was following the system laid down over a century earlier by that greatest of all classifiers, the Swedish naturalist Carl Linnaeus. The Chinese sage Confucius said that it was “a wise man” who specified the names of things, and by happy coincidence this was the name, in Latin, that Linnaeus chose for the human species: Homo sapiens. Before Linnaeus there were many different ways of naming and grouping plants and animals, often based at random on particular features that they showed—color, say, how they moved around, or what they ate. But Linnaeus believed in grouping living things by the bodily features they shared, and at the heart of his system were the two names applied to every natural kind, or species: its group or genus name capitalized, and its particular species name. Thus Homo (“Man”) and sapiens (“wise”). The system is a bit like a surname (the genus name Homo) and a first name (differentiating the different children with a particular surname, in our case sapiens). In the most-cited tenth edition of his book Systema Naturae (1758) he also named four geographic subspecies: “europaeus,” “afer,” “asiaticus,” and “americanus,” introducing some dubious anecdotal behavioral distinctions in line with then current European notions about the superiority of the European subspecies. For example, while “europaeus” was, of course, governed by laws, “americanus” was governed by customs, “asiaticus” by opinions, and the African subspecies “afer” by impulse.
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