African Exodus: The Origins of Modern Humanity

by Chris Stringer, Robin McKie

A Choice Outstanding Academic Book
A Library Journal Best Sci-Tech Book
A New York Times Notable Book

Once in a generation a book such as African Exodus emerges to transform the way we see ourselves. This landmark book, which argues that our genes betray the secret of a single racial stock shared by all of modern humanity, has set off one of the most bitter debates in contemporary science. "We emerged out of Africa," the authors cont, "less than 100,000 years ago and replaced all other human populations." Employing persuasive fossil and genetic evidence (the proof is in the blood, not just the bones) and an exceptionally readable style, Stringer and McKie challenge long-held beliefs that suggest we evolved separately as different races with genetic roots reaching back two million years.

Genres: Science, Nonfiction, History, Anthropology, Evolution, Biology, Africa

304 pages, Paperback

First published February 7, 1995

About the author

Professor Christopher Brian Stringer, Fellow of the Royal Society currently works at the National History Museum, London, as research leader in human origins.

Reviews

[Jamie Smith · Rating 4 out of 5]

If you want to start a fight with a group of paleoanthropologists, propose a human family tree. The evidence is so fragmentary, and the interpretations so varied that there are multiple schools of thought, each convinced that it is right and happy to call the others idiots in print and in person.

Broadly speaking, however, the majority of experts believe that Homo habilis was the first member of genus Homo, evolving from Australopithecus about 2.8 million years ago (MYA). Habilis then gave rise to H. erectus about 2 MYA, who spread through Africa, Europe, and Asia, surviving for an astonishingly long time, until about 100,000 years ago in China. Among the groups of erectus which migrated out of Africa, one evolved into H. heidelbergensis around 600,000 years ago, although some paleoanthropologists do not consider it different enough from erectus to be classified as a separate species. Then, sometime between 350,000-400,000 years ago further changes within the European lineage led to Neanderthals, Denisovans, and possibly some other extinct types of humans which exist only as ghostly traces in our DNA. The African line of heidelbergensis evolved into Homo sapiens around 300,000 years ago and 50,000 years ago some of them left Africa to begin the great exodus that has led to our modern world.

This model of human evolution, in its various forms and clarifications, is known as the Out of Africa hypothesis, and Chris Stringer, author of African Exodus, is one of its leading theorists. It is also, by a wide margin, the most widely accepted view held by the people who study the origins of humankind. There are, however and inevitably, other interpretations, the Multiregional hypothesis being the most frequently cited. This maintains that modern humans evolved in various places in Europe, Asia, and Africa, maintaining just enough contact – that is, interbreeding – to keep the species more or less in sync. Madelaine Böhme’s 2019 book Ancient Bones explains the theory for general readers, and while I am in no way knowledgeable enough to hold an opinion which I would care to defend, she does make an interesting, evidence-based case for her position.

The timeline of human evolution is always provisional, and its assumptions open to reinterpretation when new archaeological evidence is discovered. For instance, Kermit Pattison’s 2020 book Fossil Men describes the finding and classification of Ardipithecus Ramidus, a 4.4 MYA fossil that may be a transitional species between apes and humans, and if so, calls into question the common assumption that humans evolved from an “ape-like” ancestor. A. Ramidus indicates that ancient human ancestors may have been upright-walking and more human than apelike. This theory has both passionate defenders and outraged opponents, because that is how paleoanthropologists do things.

African Exodus was published in 1996, which is ancient by modern paleoanthropology standards, but it is nevertheless informative and well researched, especially in its account of the ways that experts have tried to fit the fossil evidence together over the decades. For this review I will highlight some of the points Stringer makes which I found illuminating, without passing judgment on Out of Africa as a whole.

At one time there were numerous species of apes, which had split from monkeys about 25 million years ago (with recent fossil finds suggesting it might have been as early as 34 million). This was long before the human-ape split, generally thought to have been 5-7 million years ago, though some argue for dates as far back as 12 million.

These large-bodied, tail-less, relatively large-brained animals were a highly successful, widespread and diverse group. Then they began to die out, losing a battle for resources with monkeys, who tend to be smaller-brained and smaller-bodied, but who nevertheless began to take over the forests of the Old World (Europe, Asia and Africa) about ten million years ago. The reasons for this shift in the primate power axis are not clear, though anthropologists believe climate change probably played a key role, since the Earth began to get cooler and drier then. In addition, some scientists point to the ability of monkeys to digest unripe fruit, a power that would have allowed them to pick off less mature produce ahead of their ape competitors. (p. 10-11)

Eventually anatomically modern features began to emerge, such as bipedalism and a more carnivorous diet. This was to have a big impact on our evolution, with nutrient-rich meat giving the extra energy that allowed brains to enlarge. Bigger brains meant more intelligence, greater social adaptability, and a better chance for survival, which encouraged even larger brains as a positive feedback loop developed. “ ‘It was not just meat, but fat and bone-marrow that were being consumed, easy to digest foods that permitted the development of smaller stomachs which used up less internal energy,’ says anthropologist Leslie Aiello.’ “ (p.25)

Evidence for this change is also found in the steadily shrinking size of the digestive tracts of these ape ancestors.

The human gut is the only energy-demanding organ that is markedly small in relation to body size compared with other mammals, while the brain is strikingly large. The latter should weigh about ten ounces for a mammal of our dimensions. In fact, the human brain today weighs almost 3 lbs. Similarly, our gut -- including stomach and intestines -- is about half its expected size. (p. 26)

As time passed the winnowing of species continued, with evolution remorselessly culling those which could not adapt to changing conditions such as climate, new predators, or the loss of food sources. “Consider the case of the early primates, the creatures from which we are descended. It is estimated from the fossil record that there must have been 6,000 different species, but only 185 are alive today.” (p. 110)

Eventually Homo sapiens evolved, a species so young that we have not had time to develop any meaningful genetic diversity. Another consideration, not mentioned in this book because the research for it came after, was the Toba supervolcano explosion of around 75,000 years ago, which expelled over a thousand times more material than the Mount St. Helens eruption, caused global cooling of 5.4-9.0°F for hundreds of years, and almost wiped out humankind. Genetic evidence supports the view that only an isolated group of 3,000-10,000 humans survived the catastrophe.

As a result, ethnicity differences between humans are almost imperceptible. “Scientists have generally recognised that the common chimpanzee of central Africa has three subspecies, though to most people they look very similar indeed. Nevertheless, these chimp ‘races’ are almost ten times as different from each other, genetically, as are the African, European, and Asian divisions of Homo sapiens.” (p. 172-173)

When the book was written, the science of genomics was in its infancy, and its arrival was not welcomed by the grizzled old bone hunters.

The old order has reacted with considerable anger to the interference of these ‘scientific interlopers.’ The idea that the living can teach us anything about the past is a reversal of their cherished view that we can best learn about ourselves from studying our pre-history. Many had spent years using fossils to establish their interpretations of human origins, and took an intense dislike to being ‘elbowed aside by newcomers armed with blood samples and computers.’ (p. 114-115)

It is humbling to consider how much of human evolution seems to have resulted from changes in the environment rather than our own heroic efforts to pull ourselves up by our genetic bootstraps, or because we are the favorites of some god-father. And yet, step by tiny step, we managed to adapt, staying one move ahead of the extinctions that claimed so many of our cousin species. The author does a good job summing up these changes when he says

our bodies could not change speedily enough [in the face of rapid climatic changes], so our brains took the strain instead. We developed a plastic, adaptive approach to the world. The result was a doubling in the expansion of our crania, a process which began around two million years ago, when Homo habilis and then Homo erectus people started to gather round the lakes of eastern Africa to make their tools and plan their scavenging and foraging (and possibly hunting). The brains had, roughly, the capacity of a pint pot, Then, slowly, we began to gain grey matter, at the rate of about two tablespoons’ worth every 100,000 years. By the time this cerebral topping-up had finished, the human cortex had more than doubled in volume. (p. 189)

There have been a number of important new findings since this book was published, and DNA analysis has had an enormous impact, in particular its ability to read the molecular clocks that tells us approximately when one species split off from another. A new edition of this book would be welcome indeed, but it is nevertheless a good non-technical introduction for anyone wishing to understand the fossil evidence supporting the Out of Africa hypothesis.

[Pam S · Rating 5 out of 5]

In African Exodus The Origins of Modern Humanity, the authors present irrefutable evidence “from the bones of the dead to the blood of the living” to reveal our common racial heritage. Published in 1996 this book is still a must read!

[Steven H · Rating 5 out of 5]

A POWERFUL EXPOSITION OF THE “OUT OF AFRICA” THEORY OF HUMAN ORIGINS

Paleoanthropologist Chris Stringer and journalist Robin McKie wrote in the Preface of this 1996 book, “For the past few years a small group of scientists has been accumulating evidence that has revolutionized our awareness of ourselves, and our animal origins. They have shown that we belong to a young species, which rose… from a crisis which threatened its very survival, and then conquered the world in a few millennia. The story … challenges many basic assumptions we have about ourselves: that ‘races’ deeply divide our populations; that we owe our success to our big brains; and that our ascent was an inevitable one. Far from it: people on different continents are closer evolutionary kin than gorillas in the same forest; Neanderthals became extinct even though they had bigger brains than Homo Sapiens; while chance as much as ‘good design’ has favored our evolution…

“It is a remarkable, and highly controversial narrative that has … been the subject of a sustained program of vilification by scientists… committed to the opposing view that we have an ancient, million-year-old ancestry. The debate… is one of the most bitter in the history of science. How these events came about and how we learned about our true nature, and our African Exodus 100,000 years ago, is explained by a scientist at the very center of the arguments and a journalist who has closely followed every twist and turn of this dramatic scientific story.”

They note that Carleton Coon’s book ‘The Origin of Races’ [1962] “was astonishingly comprehensive”; in it “Coon adopted all [Franz] Weidenreich’s arguments and then exaggerated them for good measure. White and Oriental populations were simply more advanced than those from Africa and Australia… Some academics might have been impressed by Coon’s paleontological erudition, but the books’ subtext stank of racism to many others. Coon was attacked with particular savagery by the distinguished geneticist Theodosius Dobzhansky… The row effectively put an end to Coon’s career as a mainstream, respected paleoanthropologist… and he became increasingly marginalized, even shunned.” (Pg. 56-58)

They summarize, “science has pieced together the story of how an upright, small-brained ape gave rise to several different hominid lines and eventually---after five million years of evolution---led to the emergence of Homo sapiens. We have also seen how… the Neanderthals… have slowly gained a place for themselves as an intelligent species in their own right---although … they are not the ancestors of human beings today, but are more like respected evolutionary siblings or even cousins… An obvious puzzle remains, however. If we did not evolve from Neanderthals, but were not much different from then, why did we replace them?” (Pg. 81-82)

They explain, “the University of California, Berkeley… in 1987 … took specimens from placentas of 147 women from various ethnic groups and analyzed each other’s mitochondrial DNA. By comparing these in order of affinity, they assembled a … sort of chronological chart for mankind, which linked up all the various samples, and therefore the world’s races, in a grand, global genealogy. The study produced three conclusions. First, it revealed that very few mutational differences exist between the mitochondrial DNA of human beings, be they Vietnamese, New Guineans, Scandinavians, or Tongans. Second… it created a tree with two main branches. One consisted solely of Africans. The other contained the remaining people of African origin, and everyone else in the world. The limb that connected the two branches must therefore have been rooted in Africa… Lastly, the study showed that African people had slightly more mitochondrial DNA mutations compared to non-Africans, implying their roots are a little older.” (Pg. 121-122)

They observe, “Of course, there was clearly no single exodus, no one triumphant army or early hunter-gatherers who were led Out of Africa toward a new world by a Paleozoic Moses. Instead, our exodus would have occurred in trickles as our ancestors slowly seeped out of the continent, expanding their hunting ranges and taking over new territory. Marta Lahr and Robert Foley of Cambridge University became they can reconstruct one such expansion that spread eastward out of the Horn of Africa about 80,000 years ago. Its populations diversified as they moved to eastern and southern Asia, forming the region’s modern ‘races.’” (Pg. 160-161)

They point out, “In the past, some … have made much of the intrinsic differences between these [‘racial/ethnic’] groups, linking them to all sorts of stereotypes---meanness, efficiency, laziness, and others. But it is a quite specific corollary of the Out of Africa theory that such ideas are outdated. The progeny of the people who found Australia 50,000 years ago, and the descendants of the tribes who poured down the Americas 12,000 years ago, as well as the heirs to all those other settlers of Europe, Africa, and Asia, share a common biological bond. They are all the children of the Africans who emerged from their homeland only a few ticks ago on our evolutionary clock. They may have… developed superficial variations, but underneath our species has scarcely differentiated at all.” (Pg. 177)

They note, “the message from the Out of Africa theory is a straightforward one. Our exodus’s timescale is so brief that only slight differences, if any, in intellect and innate behavior are likely to have evolved between human populations.” (Pg. 183) They add, “the story of our African Exodus makes it unlikely there are significant structural or functional differences between the brains of the world’s various peoples. We came out of Africa as an already advanced species and those who remained on the continent retained that sophistication, just as much as the rest of Homo sapiens used it to conquer the world.” (Pg. 190)

They acknowledge, “not surprisingly, our theory has made a great impact in black communities, particularly in the U.S. … [Some] Afrocentrists and black supremacists have turned the eighteenth-century European idea of nonwhite degeneracy on its head to argue that, by losing their melanin skin pigment when they left Africa, whites became inferior to blacks. ‘Melanists’ argue that because blacks have higher levels of this substance in their bodies they are more sensitive and coordinated than whites. However, there is no good scientific evidence to support this view either.” (Pg. 246)

This book will be “must reading” for anyone studying the Out of Africa theory, or related fields.

[Ruth · Rating 4 out of 5]

This was a quite informative but not at all difficult read. I can't speak to its credibility, not being a scientist. It helped me to get all the different hominid fossils that have been found straight in my head.

[Alex Lang · Rating 5 out of 5]

Excellent

Though about 20 years out of date, this is a dynamite book that clearly explicated the role of (and specialness of) Homo sapiens in the context of other hominids

[Ken Cohen · Rating 5 out of 5]

if you want a well-written survey on the latest science on human evolution, this is it.

[Jim · Rating 3 out of 5]

We are all Africans under the skin.

While at one point we thought human differences started many millennia ago, maybe we all descend from a common ancestor that came out of Africa less than 100,00 years ago. (This may be, ironically, closer to the young earth theory than previous theories of human evolution. :) Well, that is closer, but not quite close!)

In fact, human races living across the globe from each other are genetically "less different…even than lowland gorillas living in a restricted geographic area…" Two humans of completely different races and cultures have much more in common genetically than 2 gorillas living across the same forest. That's weird. And interesting. It shows we are all much more alike than many of us want to think.

And it dashes against the rocks racial differences suggested by some scientists (like the authors of The Bell Curve: Intelligence and Class Structure in American Life ).

This book is heavy on the information. I'm sure it doesn't help that a lot of this is new to me. Maybe I should have started with more of a primer. But it was good in describing - or arguing for - how man migrated originally from Africa. I honestly don't have the background in this field to evaluate it, but it gives compelling evidence. I'd be interested in seeing if current theories (this book now being 20 years old) agree.

More research!

[Shope · Rating 4 out of 5]

Good for Montessori educators

[Bernie_dunham · Rating 5 out of 5]

We are all Africans.