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Humanity's Descent: The Consequences of Ecological Instability

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In this well-written, comprehensive study, Rick Potts has provided a landmark book on human evolution. Looking beyond scattered fossils and debates over African origins or Multi-regional evolution of modern man, he views vast stretches of time and space. What made a primate species descend from a forest canopy to become a skilled survivor on the African savannah. How did it happen and when, he asks. In answer, he provides a detailed examination of the environmental history surrounding and influencing our path. We are still on that path, he reminds us. We cannot separate ourselves from our surroundings. Nor did we "overcome" the conditions nature set as we evolved. Instead, conditions drove our evolution.

Potts surveys the remote past to set his theme - climate varies, sometimes catastrophically. It may also change with stunning rapidity - as his noting of a Canadian site showing tundra becoming spruce forest in 150 years suggests. There may be long periods of relative stability, as when Pangaea, home to the dinosaurs, dominated the scene. At one time Antarctica had no ice sheet and the North Pole was tropical. Continental breakup changed more than the landscape, it revised the weather. This was no more true than in the Miocene [24 to 5.3 Mya] when weather patterns changed drastically. And continued to change.

While all this meteorological madness was occurring, a certain primate species in Africa confronted the challenges shifting weather offered. Overturning the old myth that early humans dropped out of the forest and learned to run, Potts shows how it was the forests that ran away. He's quick to point out, however, that this was not a gradual nor a steady change. Forests came and went, only to return. Lakes filled and dried, then filled. In order to survive, this primate population needed to adapt. Some did, but others failed the challenge. Those who succeeded, he argues, learned to follow the best scenario for survival. Hence, humans began their great migrations across the globe.

When those migrations, combined with improved brain power, led humans to begin transforming their environment with agriculture, that transition wasn't as revolutionary as most anthropologists usually contend. To Potts, it was simply an extension of the habits learned over the millennia. Weather changes had been adapted for. Changing the local environment by "controlling" it was simply another logical step in the sequence. However, he reminds us, cultural growth, by which innovation is admired and becomes part of tradition, turned this adaptation into a philosophy. "Dominion over the Earth" became a set piece of human thinking. It's a dangerous philosophy leading us to make irrational choices in our dealings with the rest of nature. Flexibility is lost as fewer species are relied upon to sustain us. He gives the example of the New England colonists transforming the existing relationship Native Americans generally enjoyed. Land use became limited in application, with whole tracts of forest and ecological balances disrupted. The time span of these events is infinitesimal in contrast with the long ages of adaptation. In thinking we can "control" what is uncontrollable, humans are flirting with disaster. [stephen a. haines - Ottawa, Canada]