Get Used to Climate Change [Excerpt]
Life has had to deal with environmental change, especially climate change, since the beginning of its existence on Earth. Species adjust or go extinct, and both have happened. For life-forms with our kinds of cells—eukaryotic, the kind with distinct organelles—the average existence of a species is about 1 million years, and, on average, one species goes extinct a year, at least of the species we have named and know, including those we know only from fossil records.
Organisms adjust to environmental change in three ways, from fastest to slowest: behaviorally, physiologically, and genetically. Ecologist Larry Slobodkin used to demonstrate the first two playfully during a lecture by picking up a piece of chalk and tossing it to one of the students. The student would duck or catch the chalk, which Larry pointed out was the behavioral response, first and fastest, and then within 20 seconds would blush, the physiological adjustment, second fastest. These, he would explain, were not only relatively fast but used little energy in a population. If these failed to make a successful adjustment, a population's genetic makeup could change, with genes transmitted to the next generation that led to characteristics better adjusted to the changed environment, obviously a much slower adjustment.
Individual mobile organisms migrate as an adjustment to climate. Plants and other non-mobile species adjust by having seeds or other propagules that move easily. Wind, water, and animals provide the major transportation. In any population there is a mixture of genetic types and, as Darwin explained a long time ago now, those better adapted to the current climate left more offspring than the less adapted, and over time a population evolved to fit the new climate. But this genetic adjustment took time, and since the climate is always changing, it could be that at any one time a population would be adjusting genetically to a climate that had been present but had passed or was passing. It was and is an eternal dance, populations never quite in perfect harmony with their present environment. If the rate of environmental change is too fast, populations cannot adjust and go extinct. Dealing with environmental change has always been part of being alive.
Early man was part of this dance between life and environment. Homo erectus, the first of our kind who left Africa, would likely have migrated as a matter of course. They may not have thought of it as migration in our modern sense; they were going where the environment, including sources of food and water, was better. Environmental change and moving along with it were only natural.
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