Mapping Human History: Unravelling the Mystery of Adam and Eve

258 Pages·2003·2.53 MB·English

by  Steve Olson

For Lynn
Contents
Introduction: The Human Pageant
I. AFRICA
1. The End of Evolution: The African Origins of Modern Humans
2. Individuals and Groups: The Divergence of Modern Humans
3. The African Diaspora and the Genetic Unity of Modern Humans
II. THE MIDDLE EAST
4. Encounters with the Other: Modern Humans and Neandertals in the Middle
East
5. Agriculture, Civilization, and the Emergence of Ethnicity
6. God’s People: A Genetic History of the Jews
III. ASIA AND AUSTRALIA
7. The Great Migration: To Asia and Beyond
8. Sprung from a Common Source: Genes and Languages
IV. EUROPE
9. Who Are the Europeans?
10. Immigration and the Future of Europe
V. THE AMERICAS
11. The Settlement of the Americas
12. The Burden of Knowledge: Native Americans and the Human Genome
Diversity Project
VI. THE WORLD
13. The End of Race: Hawaii and the Mixing of Peoples
Notes
Acknowledgments
A Note on the Author
Introduction
The Human Pageant
Anyone walking along the sidewalk of a large city can’t help but be struck by
the incredible variety of human beings — tall and short, fat and lean, hairy and
hairless. Some have skin the color of heavy cream; others are as dark as
bittersweet chocolate. The shapes of people’s faces, the colors of hair and eyes,
the contours of eyes, noses, and lips are marvelously unique. Partly we’re
attuned to these differences because we use them to identify people we know.
But our diversity is not an illusion. Human beings really are one of the most
physically varied species on earth.1
People tend to use these different appearances to draw conclusions about the
ancestry of others. In the Americas and Europe, if you have dark skin, people
assume that you have African ancestors, though dark-skinned peoples also come
from southern India, Australia, and parts of southeastern Asia. Individuals whose
eyelids have an extra fold of skin are assumed to be from Asian families, though
not all Asians have an epicanthic fold, as it is called, and non-Asians scattered
from southern Africa to the Americas do. A prominent nose, deep-set eyes, and
light skin identify a person as having European ancestors, though people with
similar features, if slightly darker skin, have lived for thousands of years in
India, Polynesia, northern Japan, and North and South America.
Our propensity to sort people into categories has, over the course of history,
contributed to immense human suffering. Entire groups have been condemned to
slaughter or slavery because of the color of their skin or the shape of their eyes.
Even today, almost all the armed conflicts in the world take place not between
nations but between groups2 separated by differences that often are interpreted in
biological terms. In places like Rwanda, the Balkans, Indonesia, and the Middle
East — to take only the most recent examples — groups of people have fought
and killed each other with an almost tribal savagery.
Elsewhere, tension between physically distinguishable groups often lurks just
beneath the surface of our everyday lives. In the United States, more than three-
quarters of African Americans and European Americans alike judge relations
between the two groups to be only fair or poor.3 In other parts of the world,
arguments over immigration and the assimilation of minorities have sparked
deadly riots and public protests. In 1900 the African-American scholar W. E. B.
Du Bois said, “The problem of the twentieth century is the problem of the color
line.”4 At the dawn of a new century, the issue of race looms larger than ever.
Groups of people vary in appearance because their ancestors had different
biological histories. But just how different were those histories? What if the
distinctive appearances of human groups are a historical accident, a biological
joke, no more substantial than masks at a costume party?
The story that I’m going to tell in this book begins in Africa, somewhere in the
high grasslands and wooded slopes of present-day Ethiopia, Kenya, and
Tanzania. More than 100,000 years ago, a small group of humans lived in this
region.5 They gathered nuts, fruits, and seeds from the countryside. They hunted
gazelles and hares and scavenged meals from the carcasses of animals killed by
other predators. They looked much like people today, with high foreheads, sharp
chins, and light, graceful bodies.
Many other humans lived elsewhere in Africa, Europe, and Asia at that time,
but they were noticeably different from us. Their forehead slanted backward
toward a low, bunched skull, and a heavy visorlike ridge protruded from just
above the eyes. These people would never have passed what anthropologists call
the subway test6 — that is, if you gave them a shave, dressed them in modern
clothes, and seated them on a subway car, they could never hope to blend in. The
other passengers would inevitably look at them and say, “That’s a mighty
strange-looking human being.”
These so-called archaic humans vastly outnumbered the small group of
anatomically modern humans living in eastern Africa. More than 1 million
archaic humans may have been scattered across the Old World,7 while the
population of modern humans may have dropped as low as a few tens of
thousands at times.
Today all the archaic humans are gone. The last one died many thousands of
years ago. Though they successfully occupied the earth for hundreds of
thousands of years, they were an evolutionary dead end.
Every single one of the 6 billion people on the planet today is descended from
the small group of anatomically modern humans who once lived in eastern
Africa.8 The group occasionally came close to extinction, but it never died out
completely, and eventually it began to expand. By about 100,000 years ago,
modern humans had moved north along the Nile Valley and across the Sinai
Peninsula into the Middle East. More than 60,000 years ago they made their way
along the coastlines of India and southeastern Asia and sailed to Australia.
About 40,000 years ago, modern humans moved from northeastern Africa into
Europe and from southeastern Asia into eastern Asia. Finally, sometime more
than 10,000 years ago, they made their way along a wide plain joining Siberia
and Alaska and spread down the length of North and South America.
Wherever modern humans encountered their archaic counterparts in Africa,
Asia, and Europe, the old-style humans eventually disappeared. Many questions
surround these encounters. According to the available evidence, the two groups
interbred very little, if at all.9 This conclusion seems totally at odds with our
knowledge of human history, which shows that groups of people have eagerly
interbred at almost every opportunity. Perhaps modern and archaic humans were
so different genetically that they were not able to produce offspring. Or maybe
they did have children, but hybrids were not accepted into bands of modern
humans, so the archaics’ physical characteristics could not enter modern
populations. We just don’t know.
How modern humans replaced their predecessors is also a mystery.
Archaeological evidence indicates that in some places bands of modern and
archaic humans lived near each other for thousands of years. Yet no signs of
warfare have been found. The cave paintings of Europe,10 some of which were
being drawn just as the archaic Neandertal people were dying out on the
continent, show plenty of violence against animals but none against other
humans.
Until a few years ago, much of what I’ve written in the last few paragraphs
was not known. Before then, the only way to learn about our ancient ancestors
was through the scattered bones and stone tools they left behind. Such evidence
is maddeningly scarce: of the several billion modern humans who lived before
the invention of agriculture,11 scientists have found the fossilized remains of
perhaps a few hundred. And the scarceness of the evidence means that each
fragment of bone and chipped rock bears a heavy burden of speculation.
But bones and stones are not the only record of our past. Each of us carries
around another record in almost every cell of our bodies. Human DNA, the long,
complex molecule that transmits genetic information from one generation to the
next, bears the indelible imprint of human history. Our DNA records the
evolution of an African ape that began walking on two legs more than 4 million
years ago. It documents the emergence of modern humans on the savannas of
eastern Africa about 7,500 generations ago. It chronicles the diversification of
modern humans into the “races” and “ethnic groups” that we recognize today.
Geneticists are just beginning to read the story written in our DNA, but
already they have discovered a saga of immense grandeur. They now can trace
the movement of modern humans out of Africa into the rest of the world. They
are beginning to piece together when and how groups of people acquired their
distinctive physical appearances and what those appearances mean. They are
learning how groups mixed and diverged over time. They are discovering the
immense gulf that separates what actually happened in the past from the stories
we tell ourselves about the past.
This is a book about history, but it is a history with a very real presence in our
everyday lives. Most of us think of ourselves as Hispanic or Chinese, white or
black, Nigerian or Norwegian, or some combination of categories. For some
people these labels mean very little, while for others they are the single most
important aspect of their identity. But no matter what importance individuals
attribute to these labels, there is no denying their continued power in modern
societies. Many people continue to think that human groups have fundamental
biological differences. They believe that outward variations in skin color, facial
features, or body shape reflect much more consequential differences of
character, temperament, or intelligence. Even when two groups are physically
indistinguishable, people tend to cite genetics as the source of group differences.
They say that the aggressiveness or religiosity or inventiveness of a group could
not possibly be learned — it must be something in the genes.
Genetics research is demonstrating otherwise. Human groups are too closely
related to differ in any but the most superficial ways. The genetic study of our
past is revealing that the cultural differences between groups could not have
biological origins. Those differences must result instead from the experiences
individuals have had.
Much of this new knowledge about our past is emerging from an unexpected
source. Research into the genetic causes of disease is simultaneously revealing
the histories of groups and of individuals.12 Biomedical researchers now realize
that they need to learn about the genetic differences between individuals to
understand why some people get sick and others remain healthy. But these
genetic differences are a consequence of human history — of the matings of
particular men and women over thousands of years. By studying those
differences, researchers are reconstructing the history of our species.
I first became interested in this story in 1987, when studies of human genetic
variation revealed that everyone on earth is descended from one woman who
lived in Africa around 150,000 years ago. Over the next few years I worked as a
writer on several projects, mostly at the National Academy of Sciences, that used
DNA comparisons to trace the evolutionary relationships of species, for instance,
or to understand the origins of a disease. Gradually I realized that human DNA is
a virtually limitless repository not just of biomedical but of historical
information, a sort of molecular parchment on which an account of our species
has been written. I began to compile articles and books on the subject, and my
stacks of documents grew.
The story contained in our DNA is rich, complex, and multilayered. In this
book I’ll look at five broad regions of the world — Africa, the Middle East, Asia
and Australia, Europe, and the Americas — with a final chapter on Hawaii. In
each section I’ll trace the history of modern humans in that part of the world
from their first appearance to the present. At times the story leads in unexpected
directions — to the origins and diversification of language, for example, or to
the experiences of particular groups such as the Jews or Han Chinese. But my
central concern will always be the same: to explore what our genetic history tells
us about ourselves and about our past, present, and future as a species.
The study of human genetic differences is one of the most contentious areas of
modern science;13 to some people, such investigations are too dangerous to
pursue. In their view, genetics research is a modern Pandora’s box that threatens
to reinforce stereotypes and limit human potential.
I see things differently. We are on the verge of conquering scourges that have
plagued human beings throughout history — hunger, disease, mental illness.
Admittedly, our new knowledge will pose great risks. We will learn about
individual susceptibility to diseases, which could change how we view our lives
and our relations to others. We will know much more about our history on this
planet, both as individuals and as members of a group. We have to find ways to
interpret, handle, and protect this powerful new information.
But we are not a species that shies away from knowledge. On the contrary, for
thousands of years human beings have sought innovative ways to do things and
to organize their lives. Genetics research has presented us with an opportunity to
relieve the world of great suffering. Turning our backs on this opportunity would
run counter to our conception of ourselves.
Many of the medical applications of genetics still lie in the future; we have
time to think about the dilemmas that those applications will pose.14 But the data
needed to reconstruct the genetic history of humanity are available right now; we
need to figure out what they mean. If the frequency of a particular genetic