Gregory Cochran and Henry Harpending. 2009.
The 10,000 Year Explosion. How Civilization Accelerated Human Evolution.
This book makes the astounding claim that our evolution has sped up 100 times faster in the past 10,000 years than the previous six million years. Even people 4,000 years ago were genetically and culturally different from us.
How do we know this?
One way is from looking at both human and chimpanzee DNA. We know we split off from chimps about 6 million years ago, so we can compare the genetic differences and thus the long-term rate of genetic change. The rate of change the past few thousand years is 100 times greater than the long-term rate over the past few million years. If we’d always evolved at such a fast rate, the difference between chimp and human DNA would be much greater than it is.
If evolution this fast seems impossible, then consider how different dogs are from wolves. It took less than 15,000 years to go from wolf to a Chihuahua. There’s no other mammal on earth with more varied forms and sizes than dogs. Dogs also vary widely in behavior. For example, some can learn much quicker than others. Border collies just need 5 repetitions of a new command to learn it and follow the command correctly 95% of the time, but a basset hound will need 80 to 100 repetitions and only obey correctly 25% of the time.
And it isn’t just a dogs appearance, dogs are much better at understanding our commands and gestures than wolves are.
Russian scientist Dmitri Belyaev created a domestic fox in just 40 years by selecting the most tame foxes in each generation.
As far as humans go, it’s pretty obvious evolution has taken place the past 50,000 years – just look at all the varieties of skin, eye, and hair color. Such skin-deep appearances were all we could see until recently, but with genetic testing we can see more than superficial differences – we also vary in bones, liver and brain function, disease resistance, etc from each other quite a bit. All of us can speak and have evolved better hearing as well to understand complex language and perhaps to better eavesdrop.
An Aside: What does this have to do with whole grains?
The earliest farmers were adapted to a diet of about 35% carbohydrates, but with agriculture that shot up to roughly 50%. Early farmers weren’t adapted to that and probably lived short and miserable lives. But it wasn’t long before a mutation occurred that tripled the ability of people to break down starch, and this spread rapidly in societies that practiced agriculture. Nicholas Wade writes about this and other mutations that have happened the past 10,000 years in Human Culture, an Evolutionary Force.
Back to the review.
For a long time scientists have been baffled about why humans made a very sudden shift about 50,000 years ago – suddenly advanced, complex art, culture, tools, and weapons came on the scene. For several decades now scientists have been trying to understand what happened.
This is different yet another stab at adding to the “prime mover” theories of why our brains grew so large so quickly. Recent evidence supports the thermal hypothesis, but there’s also Man the Hunter, tool making, speech, social intelligence, taming fire, cooked food, ice ages and rapid climate changes (the past 10,000 years have had the most stable weather for millions of years), etc. Most likely of all is Peter Corning’s synergy theory – we’re due to a mix of all of the above, which ratcheted the evolution of our brains rapidly, as he explains brilliantly in “Nature’s Magic”.
Once culture evolved, we were no longer bound by natural selection
We didn’t need to evolve fur when we moved to colder climates, because we could make warm clothes. We didn’t need to evolve strong muscles to hunt large animals. Once we had weapons, humans didn’t have to be muscular heavy hulks risking their lives every time they hunted. We became smaller, needed less food, and perhaps that’s why we out-competed Neanderthals.
But how could we have evolved so rapidly 50,000 years ago? Here’s the bombshell theory – we interbred with Neanderthals!
This book came out before the recent discovery that we do indeed have from one to four percent Neanderthal DNA (those of non-African descent). But none of the articles about this discussed the implications – that this is why we underwent such an explosive cultural change roughly 50,000 years ago and became fully modern humans.
The authors say a common misconception is that Neanderthals were closer to apes than people, but that is not at all true. They also had large brains, speech, and cooperated with each other when they hunted.
We had too small a population to have enough mutations to evolve quickly, the only way it makes sense for this sudden change to have happened is for us to have acquired useful genes from Neanderthals. All it would have take is for a few dozen half human – half-Neanderthal babies over thousands of years for us to gain their best genetic strengths.
It would be interesting to know if it was mainly male humans and female Neanderthals or the reverse. Such analyses were done on the ancestry of Mexicans, and their maternal ancestry is mainly Amerindian, but their paternal ancestry is Spanish.
Ultimately, the most important result of our recent evolution was our ability to innovate. Every new innovation led to new selective pressures, which caused us to evolve in new ways. The most important innovation, and the one that caused the most evolution the past 10,000 years, was the invention of agriculture.
Once we had agriculture, the human population grew enormously, which meant a much larger pool of potentially beneficial mutations happening – 100 times more than in the Pleistocene.
Agriculture also created diets early farmers weren’t adapted to. They ate way more carbohydrates and less protein, didn’t get all the vitamins they needed, and lived much shorter and unhealthier lives.
But mutations arose that changed that. Here’s just one example (that you may know): About 8,000 years ago the ability to drink milk as an adult arose in Europe, and now about 95% of people in Denmark and Sweden have no problems with digesting dairy products, and 80% of the rest of Europeans, on average. A different mutation that did the same thing arose in East Africa, and now 90% of the Tutsi are lactose tolerant. Densely populated areas evolved disease resistance, the ability to drink alcohol, and many other non-skin-deep abilities that we can now “see” with genetic studies.
At times in the Old World, when war wasn’t the main source of deaths, famine and malnutrition limited populations that reached carrying capacity. The poorest were so short on food that they didn’t reproduce themselves, while the elite had more than the two children required to replace themselves and had twice the number of surviving offspring as the poor. The least successful rich children became the new farmers, with the result that after a thousand years or so, everyone was descended from the wealthy classes.
Once the ruling elites existed, they didn’t have a hard time controlling farmers, who couldn’t leave their land in protest, or they’d die, which stuck them with paying whatever taxes, being conscripted into wars and in general endure whatever the elites dished out.
The authors suggest that in the end, people were ultimately domesticated by elite rulers, who weeded out aggressive fighting peasants, just as farmers weed out their most aggressive animals. The elites selected for a population that submitted to authority. Attention deficit disorder doesn’t exist in China – the elites completely bred that behavior out of the population. I found the whole idea fascinating and scary, the full discussion is on pages 110-113. Maybe that explains why Americans have allowed the greatest disparity in wealth between rich and poor in our nation’s history to exist, haven’t marched with torches and pitchforks on Wall Street, and so on.
A chapter of the book is devoted to why Ashkenazi Jews are so much brighter than other populations. Although they comprise less than one in 600 people, they’ve won one in four of all Nobel science and too many other achievements to list here. Basically the hypothesis is that because they were forced to hold difficult white collar jobs for centuries in finance and related areas, and couldn’t marry outside their group, evolution selected for intelligence. Unfortunately, this selection comes with genetic disorders of Tay Sachs and other diseases.
Well of course the problem with book reviews is that they’re too short and have no peer-reviewed scientific references, unlike the book, nor can the logic and details be explained, so if you think any or all of the above is crazy, read the book. And if you’re at all interested in the mystery of how we evolved, this fills in a few of the puzzle pieces I haven’t seen explained elsewhere