The 10,000 Year Explosion


Gregory Cochran and Henry Harpending




Date Reviewed:

December 10, 2010

he 10,000 Year Explosion is subtitled How Civilization Accelerated Human Evolution. It is a thought provoking subtitle, and the material presented in the book is interesting, but in the end the book failed to convince me that civilization has indeed accelerated human evolution.

The opening paragraph of the book states that Imhotep (an Egyptian chancellor) and Sargon (an Assyrian tyrant), both of whom lived 4000 years ago, were different genetically than modern humans. But just how different are they? What are the dramatic changes in the human genome over the last 4000 years? The authors don't offer much evidence. There are several recent human evolutionary changes described in the book: resistance to diseases from domesticated animals, light colored skin and eye color, lactose tolerance (ability to digest milk as an adult), and the superior intelligence of a small group called the Ashkenazi Jews. But even today, not all people have light skin, nor is everyone able to digest milk, and certainly not everyone is a Jew. Who knows what level of disease resistance was around 4000 years ago, certainly animals were domesticated earlier than that. It seems that Imhotep and Sargon were, in fact, quite similar genetically to billions of humans alive today, that Cochran and Harpending are unable to identify any major changes between them and the majority of people living today.

The first fifty pages of this book talk about the possibility that humans and Neanderthals interbred. Apparently, there is recent research that indicates modern humans may contain genes from that vanished branch of the human tree. This is an interesting topic, but I didn't understand what it had to do with the central topic of the book. After all, the last Neanderthals died out 25,000 year ago, before the end of the last ice age, and long before civilization and agriculture began with modern humans.

Cochran and Harpending argue that people who lived in the northern climes of Europe lost their dark skin color - light skin allowed them to synthesize Vitamin D more readily in an environment where sunlight is rare half of the year. This is not a controversial arguement, nor is it a new idea. But again, how did civilization cause this mutation? Didn't light skinned people exist before agriculture? A quick glance on internet suggest light skin evolved in Europeans 6,000 to 12,000 year ago. Agriculture began in the Middle East around 10,000 years ago. Perhaps they are indepentent events.

Another section of this book describes an early culture called the Proto-Indo Europeans. The authors suggest that these people arose in central Asia, and developed a favorable mutation that allowed them to digest milk. This advantage was such a benefit that the Proto-Indo-Europeans were able to spread throughout Europe and down into the Indian subcontinent which is why so many in languages in India and Europe have the same roots. Did this spread of the Indo-Europeans occur before the advent of agriculture? How does civilization result in milk drinking? It seems to me that nomad cattle herders would be just as likely to develop a mutation that allows them to digest lactose.

The book gives us examples of how civilization may have changed humanity. For example, IF there is a gene for working hard and deferring gratification, then it is possible that families that are hard workers will leave more offspring. But is there indeed a gene for working hard? And would the subtle advantages offered by the hard working gene be swamped by other factors such as disease resistance or your economic status? For example, this book tells us that your societal rank plays a huge factor in how many of your progeny survive. Kings and aristrocrats had enough wealth to leave many children, surely this effect swamped any benefit a hard working gene may have deferred to a poor peasant. Genghis Khan apparently has 16 million direct descendants due to his liberal use of harem women.

Ultimately, this book failed to convince me that civilization has dramatically changed the rate of human evolution. It identifies a few genetic changes that occur recently, but other than the Ashkenazi Jews, it is not clear that civilization was any factor in these changes, nor is it clear from the evidence that the rate of mutations has increased. Yes, it makes sense that with 6 billion humans alive now that there OUGHT be many more mutations. But the authors did not offer enough evidence to me that the genetics of civilized humanity are actually changing faster than a normal evolution model.