[W]e can calculate our way into regions of miraculous improbability far greater than we can imagine as plausible. Let's look at this matter of what we think is plausible. What we can imagine as plausible is a narrow band in the middle of a much broader spectrum of what is actually possible. Sometimes it is narrower than what is actually there. There is a good analogy with light. Our eyes are built to cope with a narrow band of electromagnetic frequencies (the ones we call light), somewhere in the middle of the spectrum from long radio waves at one end to short X-rays at the other. We can't see the rays outside the narrow light band, but we can do calculations about them, and we can build instruments to detect them. In the same way, we know that the scales of size and time extend in both directions far outside the realm of what we can visualize. Our minds can't cope with the large distances that astronomy deals in or with the small distances that atomic physics deals in, but we can represent those distances in mathematical symbols. Our minds can't imagine a time span as short as a picosecond, but we can do calculations about picoseconds, and we can build computers that can complete calculations within picoseconds. Our minds can't imagine a timespan as long as a million years, let alone the thousands of millions of years that geologists routinely compute. Just as our eyes can see only that narrow band of electromagnetic frequencies that natural selection equipped our ancestors to see, so our brains are built to cope with narrow bands of sizes and times. Presumably there was no need for our ancestors to cope with sizes and times outside the narrow range of everyday practicality, so our brains never evolved the capacity to imagine them. It is probably significant that our own body size of a few feet is roughly in the middle of the range of sizes we can imagine. And our own lifetime of a few decades is roughly in the middle of the range of times we can imagine.
Long before there were effective treatments, physicians dispensed prognoses, hope, and, above all, meaning. When something terrible happens-and serious disease is always terrible-people want to know why. In a pantheistic world, the explanation was simple-one god had caused the problem, another could cure it. In the time since people have been trying to get along with only one God, explaining disease and evil has become more difficult. Generations of theologians have wrestled with the problem of theodicy-how can a good God allow such bad things to happen to good people? Darwinian medicine can't offer a substitute for such explanations. It can't provide a universe in which events are part of a divine plan, much less one in which individual illness reflects individual sins. It can only show us why we are the way we are, why we are vulnerable to certain diseases. A Darwinian view of medicine simultaneously makes disease less and more meaningful. Diseases do not result from random or malevolent forces, they arise ultimately from past natural selection. Paradoxically, the same capacities that make us vulnerable to disease often confer benefits. The capacity for suffering is a useful defense. Autoimmune disease is a price of our remarkable ability to attack invaders. Cancer is the price of tissues that can repair themselves. Menopause may protect the interests of our genes in existing children. Even senescence and death are not random, but compromises struck by natural selection as it inexorably shaped out bodies to maximize the transmission of our genes. In such paradoxical benefits, some may find a gentle satisfaction, even a bit of meaning-at least the sort of meaning Dobzhansky recognized. After all, nothing in medicine makes sense except in the light of evolution.