Gregory Cochran and Henry Harpending claim that human evolution has accelerated in the last 10,000 years. In one sense this has to be correct since the number of humans is increasing exponentially and that means far more mutations are occurring every generation. Many of those new mutations are contributing to a significant increase in variation.But that's not what they mean. They claim that adaptations have increased. When they talk about accelerated human evolution they are mostly talking about an increase in natural selection.
For those of you who have not read the book, I thought I'd give you some of the examples that feature prominently in the opening chapter.
... when humans hunted big game 100,000 years ago, they relied on close-in attacks with thrusting spears. Such attacks were highly dangerous and physically taxing, so in those days, hunters had to be heavily muscled and have thick bones. That kind of body had its disadvantages—if nothing else, it required more food—but on the whole, it was the best solution in that situation. But new weapons like the atlatl (a spearthrower) and the bow effectively stored muscle-generated energy, which meant that hunters could kill big game without big biceps and robust skeletons. Once that happened, lightly built people, who were better runners and did not need as much food, became competitively superior. A heavy build was yesterday's solution: expensive, but no longer necessary. (p. 3)
With the invention of nets and harpoons, fish became a more important part of the diet in many parts of the world., and metabolic changes that better suited humans to that diet were favored. (p. 4)
Close-fitting clothing provided better protection against cold, allowing people to venture farther north. In cool areas, people needed fewer physiological defenses against low temperatures, while in the newly settled colder regions they needed more such defenses, such as shorter arms and legs, higher basal metabolism, and smaller noses. (p. 4)
With the advent of new methods of food preparation, such as the use of fire for cooking, teeth began to shrink, and they continued to do so over many generations. Pottery, which allowed storage of liquid foods, accelerated that shrinkage. (p. 4)
As the complexity of human speech approached modern levels, there must have been selection for changes in hearing (both changes in the ear and in how the brain processes sounds) that allowed better discrimination of speech sounds. Think of the potential advantages in being just a bit better at deciphering a hard-to-understand verbal message than other people: Eavesdropping can be a life-or-death affair. (p. 4)
... we believe that the obvious difference between racial groups are linked to gene variants that have recently increased in fitness and had major fitness effects. Blue eyes, found only in Europeans and their near neighbors, are a result of a new version of the DNA that controls the expression of OCA2 that has undergone strong selection, at least in Europe. (p. 18)
Dry earwax is common in China and Korea, rare in Europe, unknown in Africa: The gene variant underlying dry earwax is the product of strong recent selection. (p. 18)
We can confidently predict that many (perhaps most) as yet unexplained racial differences are also the product of recent selection. For example, we argue that the epicanthic eyelid found in the populations of northern Asia is most likely the product of strong and recent selection. (p. 18)
