Map of life expectancy at birth from Global Education Project.

Saturday, March 04, 2006

A Paradox of Reason

The hope of early philosophers of The Englightenment was that through reason, we could fully understand the universe and explain all that is. Even today, most laypeople, and for that matter many scientists, are in the habit of thinking that the test of scientific ideas is successful prediction. Positivism, the leading philosophical school of 20th Century science, maintains that the meaning of a statement is equivalent to the means by which it can be verified, in other words that the proof of the pudding is in the eating.

But science has a perplexing secret. Okay, not really a secret, it's out in the open. But it hasn't completely sunk in. It turns out that a good percentage of scientific assertions are not determinist, but probabilistic. Much of scientific explanation is based on what are called stochastic, or random, processes. Indeed, the universe, at the most fundamental level, is now understood to be a realm of chance, of events that cannot be predicted. At the smallest scales, particles and energy flicker in and out of existence in a chaotic foam. Innumerable random events of particular probabilities add up to a larger scale, the scale of our perceptions, which is predictable to a higher degree of probability, but even in our macroscopic realm chance and chaos persist.

Evolution is one field of profound meaning to humans in which stochastic processes rule. Our culture has a deeply ingrained habit of thinking of evolution as a deterministic process, one that tends toward a goal, is governed by purposes and aspirations. Even scientists who work in the field use deterministic and teleological metaphors. (Teleology means the philosophy that there is design or purpose in nature.) Richard Dawkins writes of "selfish" genes. Epidemiologists speak casually of the reproductive "task" and "strategies" of viruses, of viruses "attacking" cells and "using" receptors.

While these metaphors are a convenient shorthand, they are misleading rather than illuminating to the general public. Evolution is governed by chance. Genetic mutation and recombination happen in an essentially random way. (It's a bit more complicated, in that the probability of particular kinds of changes is influenced by genetic repair mechanisms, mechanisms of reassortment and recombination, etc. But they still occur unpredictably.) We think of natural selection as shaping these random events into a definite direction, but that is equally faulty. The "fittest" organism may happen to be unlucky, and leave no progeny. For example, it could be buried under a volcanic eruption, or have the bad luck to be the mouse that was spotted by the hawk even though its camouflage was a bit better than its sibling that was under a log at that moment. We can study the results of evolution, but we cannot predict its future, nor are those results fully explainable. They were certainly not inevitable.

Evolution didn't have to produce us, or sea anemomes, or smallpox. It just happened to. We aren't the culmination of any process or a step on the way to anything else. We just are. The biosphere is complex, fascinating, amazing. But if we were able to start up a second earth and let it run for 4 1/2 billion years, we would wind up with something completely different.

That isn't very satisfying, I know, which is the main reason that most people don't believe it. Get used to it.

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