Free A Troublesome Inheritance: Genes, Race and Human History by Nicholas Wade

later start and the great empires of the Incas and Mayans emerged several thousand years later than their counterparts in Eurasia. In a fifth race, the peoples of Australia and Papua New Guinea, population numbers were always too low to ignite the processes of settlement and state building.

How Evolution Creates Different Societies
    People are entirely different from ants, yet there is something to be learned from the creatures that occupy the other pinnacle of social evolution in nature. An ant is an ant is an ant, yet natural selection has crafted a profusion of widely different ant societies, each adapted to its own ecological niche. Leaf-cutter ants are superb agriculturalists, tending underground gardens of a mushroomlike fungus which they protect with special antibiotics. There are ants that live in the hollow thorns provided for them by acacia trees. Some ants specialize in preying on termite nests. Weaver ants sew leaves together to construct shelters for their colonies. Army ants kill every living thing that cannot escape from their intense raiding parties.
    In the case of ants, evolution has generated their many different kinds of society by keeping the ant body much the same and altering principally the behavior of each society’s members. People too live in many different types of society, and evolution seems to have constructed these with the same strategy—keep the human body much the same but change the social behavior.
    A principal difference is that people, with their far greater intelligence, construct societies full of complex interactions in which an individual with stereotyped behavior like an ant’s would be at a severe disadvantage. Learned behavior, or culture, plays a dominant role in human societies, shaped by a small, though critical, set of genetically influenced social behaviors. In ant societies, by contrast, social behavior is dominated by the genes and the genetically prescribed pheromones that govern the major activities of an ant society.
    In human societies, individuals’ behavior is therefore flexible and generalist, with much of a society’s specificity being embedded in itsculture. Human societies are not nearly as diverse as those of ants because evolution has had a mere 50,000 years in which to shape modern human populations, compared with the 100 million years of ant evolution.
    Another major difference is that among people, individuals can generally move easily from one society to another. Ants will kill ants from other species or even a neighboring colony of the same species. Apart from slavery—some species of ant will enslave other species—ant societies are immiscible. The institutions of ant societies are shaped almost entirely by genetics and little, if at all, by culture. There is no way that army ants can be trained to stop raiding and turn to peaceful horticulture like leaf-cutter ants. With human societies, institutions are largely cultural and based on a much smaller genetic component.
    In the case of both ants and people, societies evolve over time as natural selection modifies the social behavior of their members. With ants, evolution has had time to generate thousands of different species, each with a society adapted to survival in its particular environment. With people, who have only recently dispersed from their ancestral homeland, evolution has so far generated only races within a single species, but with several major forms of society, each a response to different environments and historical circumstances. New evidence from the human genome now makes it possible for the first time to examine this differentiation of the human population at the genetic level.

Evolution and Speciation
    Races are a way station on the path through which evolution generates new species. The environment keeps changing, and organisms will perish unless they adapt. In the course of adaptation, different variations of a species will emerge in conditions where the species faces