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Day 17 (July 12, 2011): Geology Walk, part II
July 12, 2011
Today we picked up where we left off in our geology walk from Sunday, July 10. Do you remember the members? The members are the major geological units of the Olorgesailie Formation, and they occur in a sequence through time.
The reason why we’re very interested in these reddened beds is that the oldest ones at Olorgesailie are about 780,000 years old, right at the bottom of the Member 8 sediments. And that date roughly corresponds to when the strongest fluctuations between glacial and warm times began to occur at higher latitudes. Could it be that those cold-warm shifts in the temperate zone magnified the dry-wet fluctuations in tropical East Africa?
Through this work I proposed an idea, 15 years ago now, that environmental variability itself was a critical factor in how populations of early human ancestors evolved better ways of adjusting to change in their surroundings. During times when environmental change was ramped up, you might imagine the benefits of having improved mental abilities, social behaviors that encouraged cooperation, new aspects of cultural learning, and eventually the ability to plan, invent innovative technologies, to imagine and think abstractly, and to create complex ways of offsetting the effects of the environment, such as by building shelters and fire, making clothing, and growing food in surplus whenever possible. The basic idea is called variability selection – times of strong shifts in the environment favored ways that improved how well human ancestors could adjust to their surroundings. These ways included, of course, the ability to modify the immediate surroundings to a greater and greater extent – a hallmark of our species today, for better or for worse.