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It’s a Small World
Mapping Human History: Discovering the Past Through Our Genes
by Steve Olson

Reviewed by
Merete Rietveld

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Steve Olson has written a book that promises one of the best stories we have ever heard: The story written in our DNA. "It has adventure, conflict, triumph, and sex—lots of sex. It ranges from jungles to deserts to icy plains, across generations and thousands of years."

Mapping Human History follows humans from Africa to Europe, Asia, the Middle East, and the Americas, tracking their movement across continents, exploring regional genetic histories, and interviewing local geneticists at every stop. Reconstructing the history of various peoples, the book points out how the historical trajectories of humans constantly overlap.

Olson, a science journalist who has also worked for the US National Academy of Sciences, tells us that everyone in the world can most likely claim Confucius and Julius Caesar among our ancestors once we trace our lineage back a couple of millennia. Population statistics proves such claims to be true, he writes. The exponential growth of our ancestors—from two parents to four grandparents, eight great-grandparents, and going back forty generations to more than a trillion direct ancestors—leads us to a time in history when, in theory, the number of ancestors would exceed the total world population.

Genetics confirms that human groups are all closely related and possess only the most superficial genetic differences. Due to the "natural human tendency to interbreed" and our species' history of migrating from continent to continent, everyone is connected to a common pool of ancestors. The author denies that human groups have significant biological differences, yet stops short of saying that race has no genetic basis.


‘We have not “evolved” since the emergence of Homo sapiens from Africa 150,000 years ago.’

Olson contends that race and ethnicity are social constructions that people have justified by assuming that biological differences exist. "Many people...cite genetics as the source of group differences...believing that outward variations in skin color, facial features or body shape reflect much more consequential differences of character, temperament, or intelligence."

While the genetic differences between ethnic groups create different physical features and propensities to certain diseases, Olson claims that these variations are "meaningless" in comparison to the natural genetic variation in humans. Still, geneticists will continue to study the slight variations between ethnic groups because they have crucial implications for biomedical and historical research.

Such studies not only look into the genetic causes of disease, but also reveal information on the merging and separation of human groups over time. Mutations—created when cells reproduce their DNA—are the "key to reconstructing our genetic history," writes Olson. Parents bequeath mutations to their children, creating a unique genetic pattern that spreads throughout certain populations. By counting the mutations that differ between two distinct DNA sequences, geneticists can find out who is related to whom and estimate the number of generations that have passed since a common ancestor existed.

Despite the genetic variations among humans, Olson claims that we have not "evolved" since the emergence of Homo sapiens from Africa 150,000 years ago. "Our basic body plan was set more than 100,000 years ago. Since then, we have been in a period of evolutionary stasis."

Throughout Mapping Human History, Olson says that human beings have never been able to resist the "urge to merge." Consequently, our species has interbred too enthusiastically to develop substantial genetic differences. The author's enthusiasm for this idea overreaches in a passage that addresses a period of cohabitation between Neanderthals and modern humans in Europe. He rationalizes that humans must have interbred with local Neanderthals because modern statistical data show that up to 50 percent of men on farms have had "sexual experiences with animals." Speculations abound in the anthropological parts of the book, but there is no provision of a convincing backup.

In the chapter entitled "The End of Evolution," Olson contends "no one group is more closely related to our ancestors than any other." However, a few paragraphs later he writes that perhaps the Bushmen of eastern Africa "retain some of the characteristics of our early modern ancestors" because they live in a place where the original Homo sapiens are thought to have lived.

In the final chapters of the book, Olson questions the practice of studying the genetics of ethnic groups. He worries that although "the only way to understand how similar we are is to learn how we differ…studies of human differences can seem to play into the hands of those who would accentuate those differences." Some may benefit from tracing their lineage back to royalty, but others could be stigmatized by possessing genes associated with disease, for example.

Olson admits that pursuing genetic knowledge implies both risks and opportunities. His lasting vision is "a world in which people are free to choose their ethnicity regardless of their ancestry."

See related GNN book review Clan Mothers and Ancient Travelers: A review of Bryan Sykes' The Seven Daughters of Eve

Merete Rietveld is a freelance writer who lives in Palo Alto, California.

Olson, Steve. Mapping Human History: Discovering the Past Through Our Genes. Houghton Mifflin Company, Boston, Massachusetts, May 2002.

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