Author: David Reich
Reviewed by: Glenn P. Hendrix, Chair, Arnall Golden Gregory LLP
I’m fascinated by prehistory. Anatomically modern humans have been around for at least 200,000 years, but the earliest recorded history dates back only a tiny fraction of that time. What was happening before people starting writing things down?
Archaeology provides some answers, but is maddeningly incomplete and subject to interpretation.
Fortunately for the curious, the last decade has yielded rapid advances in extracting and processing ancient DNA, taken from bones that are thousands or even tens of thousands of years old.
Who We Are and How We Got Here, by David Reich, professor of genetics at Harvard Medical School, describes how the study of ancient DNA – also known as “paleogenetics” – is supplementing, and in some cases upending, conventional wisdom about human prehistory and how we came to populate every corner of the planet.
Scholars once debated whether humans migrating out of Africa interbred with Neanderthals (and their recently discovered cousins, Denisovans). Neanderthals coexisted with anatomically modern humans in parts of Europe, the Near East and Central Asia until around 30,000 years ago, when they became extinct. Genomic testing shows that interbreeding did occur, as modern humans carry Neanderthal and Denisovan genes.
As related by Reich, the study of ancient DNA also shows that most Europeans today descend from three divergent populations which came together within the past 10,000 years. Farmers brought agriculture from what is now Turkey into Europe around 9,000 years ago and mixed with hunter-gatherers living there. By about 5,000 years ago, most Europeans were descended largely from these Anatolians.
[pullquote]As Reich puts it: “Ideologies that seek a return to a mythical purity are flying in the face of hard science.” [/pullquote]
DNA findings have also settled a decades-long academic dispute about how cultural innovations like pottery techniques, tool-making, burial practices and such were spread. One school of thought was that they arrived via proselytization and imitation as hunter-gatherers adopted new ways of life. It turns out that these were largely introduced through population replacement as migrants supplanted indigenous inhabitants.
A third wave of migrants hit Europe around 5,000 years ago. The so-called “Yamnaya” people came from the Eastern steppes, a mix of peoples from modern-day Iran and the northern Caucasus. Their grave goods suggest that they celebrated violence, and unlike the farmers then inhabiting Europe, they had mastered the wheel and horse.
Some of the DNA findings can be viewed as disturbing. European male ancestry (traced through the Y chromosome, passed solely through the paternal line) is overwhelmingly Yamnaya-derived, whereas mitochondrial DNA passed through the female line is not.
Reich avoids saying plainly what this must mean, but his dry academic-speak doesn’t quite do justice to what must have been horrifying times for the vanquished.
These times may not reflect well on human nature, but some counterbalance is offered by archaeological evidence suggesting that European societies predating the Yamnaya expansion were more egalitarian and less violent than those that followed.
The Yamnaya also moved east and south into the Indian subcontinent. Modern Indians are mostly a genetic mix of these migrants (termed by Reich as “Ancestral North Indians”) and the more indigenous, predominantly Dravidian language speakers of southern India (“Ancestral South Indians”), themselves descendants of agricultural peoples. The genetic differences persist today in India’s caste system. For example, Brahmins, the priestly caste, tend to have more Yamnaya genes.
Scholars have long-puzzled over the origin of Indo-European languages, which range from English to Russian to Hindi. It appears that the spread of Yamnaya culture is the common thread.
Other chapters discuss the genomic origins of East Asians, the genetic ancestry of Native Americans (making the case for an early crossing from Asia before the Bering land bridge was fully formed), the migrations that populated Oceania and more. It’s all engrossing.
While the book has sparked concerns that we may read too much into genetic differences between populations, one overriding lesson is that humans have always been migrating and mixing. We’re all essentially “mutts.”
As Reich puts it: “Ideologies that seek a return to a mythical purity are flying in the face of hard science.”
Read some of Mr. Hendrix’s previous reviews:
Editor’s note: This review is part of Global Atlanta’s annual project asking influential readers and community leaders to review the most impactful book they read during the course of the year. This endeavor has continued each year since 2010. Purchases through the Amazon affiliate links at top will provide a commission to Global Atlanta. All books were chosen and reviews written independently, with only mild editing from our staff.