Evolution, the cause of the diversity of biological life on Earth, does not work like humans do, and does not design things the way a human engineer would. This blind idiot god is also the source and patterner of human beings. "Nothing in biology makes sense except in the light of evolution," said Theodosius Dobzhansky. Humans brains are also biology, and nothing about our thinking makes sense except in the light of evolution.

Consider, for example, the following tale:

A man and a woman meet in a bar. The man is attracted to her form and clear complexion, which would have been fertility cues in the ancestral environment, but which in this case result from makeup and a bra. This does not bother the man; he just likes the way she looks. His clear-complexion-detecting neural circuitry does not know that its purpose is to detect fertility, any more than the atoms in his hand contain tiny little XML tags reading "<purpose>pick things up</purpose>". The woman is attracted to his confident smile and firm manner, cues to high status, which in the ancestral environment would have signified the ability to provide resources for children. She plans to use birth control, but her confident-smile-detectors don't know this any more than a toaster knows its designer intended it to make toast. She's not concerned philosophically with the meaning of this rebellion, because her brain is a creationist and denies vehemently that evolution exists. He's not concerned philosophically with the meaning of this rebellion, because he just wants to get laid. They go to a hotel, and undress. He puts on a condom, because he doesn't want kids, just the dopamine-noradrenaline rush of sex, which reliably produced offspring 50,000 years ago when it was an invariant feature of the ancestral environment that condoms did not exist. They have sex, and shower, and go their separate ways. The main objective consequence is to keep the bar and the hotel and condom-manufacturer in business; which was not the cognitive purpose in their minds, and has virtually nothing to do with the key statistical regularities of reproduction 50,000 years ago which explain how they got the genes that built their brains that executed all this behavior.

This only makes sense in the light of evolution as a designer - that we are poorly optimized to reproduce by a blind and unforesightful god.

The idea of evolution as the idiot designer of humans - that our brains are not consistently well-designed - is a key element of many of the explanations of human errors that appear on this website.

Some of the key ideas of evolutionary psychology are these:

People's brains do not explicitly represent evolutionary reasons, consciously or unconsciously.
We are optimized for an "ancestral environment" (often referred to as EEA, for "environment of evolutionary adaptedness") that differs significantly from the environments in which most of us live. In the ancestral environment, calories were the limiting resource, so our tastebuds are built to like sugar and fat.
The brain is not built the way a human engineer would build it. A human engineer would have built our bodies to measure what it needed, so that if you already had enough calories but were lacking micronutrients, your taste buds would start liking lettuce instead of cheeseburgers.
The brain is a giant hack that starts to break down when you try to do things with it that hunter-gatherers weren't doing. Like computer programming, say.
Evolution's purposes also differ from our own purposes. We are built to deceive ourselves because self-deceivers were more effective liars in ancestral political disputes; and this fact about our underlying brain design doesn't change when we try to make a moral commitment to truth and rationality.
Although human beings do absorb significant additional complexity in the form of culture, we don't absorb it in a fully general way, but rather, in the way that we evolved to absorb it. That's why the Soviets couldn't raise perfect communist children. Children are programmed to absorb their parents' language, say, but there is no environment which evokes the response of perfect altruism in human children.

External links

The Psychological Foundations of Culture by Leda Cosmides and John Tooby.
Evolutionary Psychology: A Primer by Leda Cosmides and John Tooby.
“Darwinian Psychologist” Straw Man’s Ass Kicked
The Moral Animal: Why We Are the Way We Are: The New Science of Evolutionary Psychology - popular book by Robert Wright.

See also

Evolution
Stupidity of evolution, evolution as alien god
Human universal
Adaptation executers
Corrupted hardware
Psychology