"Nothing in biology makes sense except in the light of evolution."
Yes, that quote is overexposed, but some things cannot be given too much honor. I am making my way through Melvin Konner's massive The Evolution of Childhood, which is wondrous as a compendium of biological and anthropological research, but not really recommended except for fans of evolution or psychobiology. For beach reading look elsewhere.
With the exception of the very real possibility of God's non-existence, which finally got through to me around age 17, I would say that no single idea has struck me with so much force as Darwin's theory. Once its awesomely simple explanatory power made itself felt, so many other seemingly unrelated phenomena clicked into place. And evolution endows humanity with the dignity of deep time and deep history. To learn that creationism is true would be like learning that the universe was switched on five minutes ago, containing the illusion of a 13.7 billion year past. As Darwin noted in wrapping up The Origin of Species, "there is grandeur in this view of life," the notion that the living world has boot-strapped its way to its current dizzying variety over 4 billion years on this planet. Each new organism, whether virus or human, is a biological hypothesis unwittingly put forth by the universe.
Perhaps I fell in love with evolution, as it were, through the writings of the archaeologist and poet Loren Eiseley, for whom the barely fathomable past of Homo sapiens held the haunting sublimity of the ocean or of deep space. For him evolution, far from answering all our questions, poses profound metaphysical and moral mysteries. If there is anything that evolution teaches, it is that our species was never inevitable, and represents no culmination. The contingency goes all the way down, and we too shall pass. There is comfort in that. This reassurance removes us (as Plato might put it) from rooms of smoke and mirrors into open sunlight, where we all find ourselves on the same endless plain.
What does evolution mean for psychiatry? Much in theory, perhaps little in practice. A few thoughts as I understand them:
1. Evolution, unlike God, does not care about our happiness. Reproductive fitness is not inconsistent with suffering, which is not to say that suffering is our normative condition.
2. Evolution, unlike God, is not perfect; it merely makes do with the conditions at hand, which leads to very imperfect designs, such as the human lower back, and perhaps, schizophrenia, mental retardation, etc.
3. Evolution operates at the level of the gene, so certain psychological conditions (of anxiety, depression, or mania) may be adaptive at lower intensities but maladaptive when (more rarely) large numbers of predisposing genes congregate in individuals. Much distress results from bad luck.
4. Evolution is always context-dependent, so certain genes (for obesity, ADHD, or substance abuse) only became problematic in environments of high caloric density, literate technocracy, or the easy availability of intoxicants, respectively.
5. Evolution helps with understanding and acceptance, but by virtue of the naturalistic fallacy (the effective is not necessarily the good) it tells us nothing about what we should value for the future. Henceforth we guide our own evolution, however hapazardly. This may be why evolution can seem to mean either everything or nothing: it has the potential to explain all, but in the form of a consciousness that could theoretically turn its back on all that (or so it seems). As a recent review of what the "post-humanists" are up to suggests, this may reflect our brilliance or our ultimate folly. Is accelerated change a threat to human nature, or the truest embodiment of human nature? Beyond a certain point self-transformation is logically and formally tantamount to suicide, is it not? Even the humble bacterium has the wisdom not to reject its own nature. Consciousness is about the always precarious integrity of identity. Would I still know you on the other side of the Singularity? Would I know myself?