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Like "IRC chat" or "TCP/IP protocol", the phrase "reproductive organ" is redundant. All organs are reproductive organs. Where do a bird's wings come from? An Evolution-of-Birds Fairy who thinks that flying is really neat? The bird's wings are there because they contributed to the bird's ancestors' reproduction. Likewise the bird's heart, lungs, and genitals. At most we might find it worthwhile to distinguish between directly reproductive organs and indirectly reproductive organs.
This observation holds true also of the brain, the most complex organ system known to biology. Some brain organs are directly reproductive, like lust; others are indirectly reproductive, like anger.
Where does the human emotion of anger come from? An Evolution-of-Humans Fairy who thought that anger was a worthwhile feature? The neural circuitry of anger is a reproductive organ as surely as your liver. Anger exists in Homo sapiens because angry ancestors had more kids. There's no other way it could have gotten there.
This historical fact about the origin of anger confuses all too many people. They say, "Wait, are you saying that when I'm angry, I'm subconsciously trying to have children? That's not what I'm thinking after someone punches me in the nose."
No. No. No. NO!
Individual organisms are best thought of as adaptation-executers, not fitness-maximizers. The cause of an adaptation, the shape of an adaptation, and the consequence of an adaptation, are all separate things. If you built a toaster, you wouldn't expect the toaster to reshape itself when you tried to cram in a whole loaf of bread; yes, you intended it to make toast, but that intention is a fact about you, not a fact about the toaster. The toaster has no sense of its own purpose.
But a toaster is not an intention-bearing object. It is not a mind at all, so we are not tempted to attribute goals to it. If we see the toaster as purposed, we don't think the toaster knows it, because we don't think the toaster knows anything.
It's like the old test of being asked to say the color of the letters in "blue". It takes longer for subjects to name this color, because of the need to untangle the meaning of the letters and the color of the letters. You wouldn't have similar trouble naming the color of the letters in "wind".
But a human brain, in addition to being an artifact historically produced by evolution, is also a mind capable of bearing its own intentions, purposes, desires, goals, and plans. Both a bee and a human are designs, but only a human is a designer. The bee is "wind", the human is "blue".
Cognitive causes are ontologically distinct from evolutionary causes. They are made out of a different kind of stuff. Cognitive causes are made of neurons. Evolutionary causes are made of ancestors.
The most obvious kind of cognitive cause is deliberate, like an intention to go to the supermarket, or a plan for toasting toast. But an emotion also exists physically in the brain, as a train of neural impulses or a cloud of spreading hormones. Likewise an instinct, or a flash of visualization, or a fleetingly suppressed thought; if you could scan the brain in three dimensions and you understood the code, you would be able to see them.
Even subconscious cognitions exist physically in the brain. "Power tends to corrupt," observed Lord Acton. Stalin may or may not have believed himself an altruist, working toward the greatest good for the greatest number. But it seems likely that, somewhere in Stalin's brain, there were neural circuits that reinforced pleasurably the exercise of power, and neural circuits that detected anticipations of increases and decreases in power. If there were nothing in Stalin's brain that correlated to power - no little light that went on for political command, and off for political weakness - then how could Stalin's brain have known to be corrupted by power?
Evolutionary selection pressures are ontologically distinct from the biological artifacts they create. The evolutionary cause of a bird's wings is millions of ancestor-birds who reproduced more often than other ancestor-birds, with statistical regularity owing to their possession of incrementally improved wings compared to their competitors. We compress this gargantuan historical-statistical macrofact by saying "evolution did it".
Natural selection is ontologically distinct from creatures; evolution is not a little furry thing lurking in an undiscovered forest. Evolution is a causal, statistical regularity in the reproductive history of ancestors.
And this logic applies also to the brain. Evolution has made wings that flap, but do not understand flappiness. It has made legs that walk, but do not understand walkyness. Evolution has carved bones of calcium ions, but the bones themselves have no explicit concept of strength, let alone inclusive genetic fitness. And evolution designed brains themselves capable of designing; yet these brains had no more concept of evolution than a bird has of aerodynamics. Until the 20th century, not a single human brain explicitly represented the complex abstract concept of inclusive genetic fitness.
When we're told that "The evolutionary purpose of anger is to increase inclusive genetic fitness," there's a tendency to slide to "The purpose of anger is reproduction" to "The cognitive purpose of anger is reproduction." No! The statistical regularity of ancestral history isn't in the brain, even subconsciously, any more than the designer's intentions of toast are in a toaster!
Thinking that your built-in anger-circuitry embodies an explicit desire to reproduce, is like thinking your hand is an embodied mental desire to pick things up.
Your hand is not wholly cut off from your mental desires. In particular circumstances, you can control the flexing of your fingers by an act of will. If you bend down and pick up a penny, then this may represent an act of will; but it is not an act of will that made your hand grow in the first place.
One must distinguish a one-time event of particular anger (anger-1, anger-2, anger-3) from the underlying neural circuitry for anger. An anger-event is a cognitive cause, and an anger-event may have cognitive causes, but you didn't will the anger-circuitry to be wired into the brain.
So you have to distinguish the event of anger, from the circuitry of anger, from the gene complex which laid down the neural template, from the ancestral macrofact which explains the gene complex's presence.
If there were ever a discipline that genuinely demanded X-Treme Nitpicking, it is evolutionary psychology.
Consider, O my readers, this sordid and joyful tale: A man and a woman meet in a bar. The man is attracted to her clear complexion and firm breasts, 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.
To reason correctly about evolutionary psychology you must simultaneously consider many complicated abstract facts that are strongly related yet importantly distinct, without a single mixup or conflation.