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The Human Ancestral Environment

In both humans and other animal species, evolved behavior patterns reflect the selective pressures of the ancestral environments. Evolutionary psychologists, following John Bowlby, sometimes speak of the EEA or environment of evolutionary adaptedness. This is the environment in which an evolved tendency was adaptive. In other words, it is the environment in which a behavior evolved. A simpler term is ancestral environment, if the term is understood to refer to the period of time when a behavior evolved, not earlier or later times.

What is the EEA, to evolutionary psychologists? What was the human EEA?

For humans, the EEA was the environment of the most recent 125,000 years or so. Lactose tolerance, the example used above, evolved only recently, in the past 2,000 years. That is extremely recent by evolutionary standards, and it shows the great advantage milk-drinking provided to people in northern climates. Many human behaviors presumably evolved during a much earlier period of pre-history.

DNA studies show that biologically modern humans emerged from a small group of approximately 1,000 individuals who lived about 100,000 years ago. The population bottleneck (ours was an endangered species at the time) made the human race genetically uniform. Geneticists say there is less variation between the DNA of humans from opposite ends of the earth than there is between gorillas or chimps from adjacent patches of jungle. The reason is that gorillas and chimpanzees experienced no population bottleneck in their recent evolutionary past, so their populations have had more time to accumulate random changes and variations. Humans, by contrast, are all very similar in their DNA.

Organized agriculture began relatively recently, about 10,000 to 20,000 years ago. After that, many groups of modern humans lived in villages. However, cultural change occurs much faster than biological change. Most human behavioral characteristics were already in place by the time humans learned to domesticate plants and animals. Most evolutionary psychologists believe the dominant social environment for evolving humans was the older, hunting-and-gathering, nomadic way of life.

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