The dominant belief on this site seems to be in the "psychological unity of mankind". In other words, all of humanity shares the same underlying psychological machinery. Furthermore, that machinery has not had the time to significantly change in the 50,000 or so years that have passed after we started moving out of our ancestral environment.

In The 10,000 Year Explosion, Gregory Cochran and Henry Harpending dispute part of this claim. While they freely admit that we have probably not had enough time to develop new complex adaptations, they emphasize the speed at which minor adaptations can spread throughout populations and have powerful effects. Their basic thesis is that the notion of a psychological unity is most likely false. Different human populations are likely for biological reasons to have slightly different minds, shaped by selection pressures in the specific regions the populations happened to live in. They build support for their claim by:

• Discussing known cases where selection has led to rapid physiological and psychological changes among animals
• Discussing known cases where selection has led to physiological changes among humans in the last few thousand years, as well as presenting some less certain hypotheses of this.
• Postulating selection pressures that would have led to some cognitive abilities to be favored among humans.

In what follows, I will present their case by briefly summarizing the contents of the book. Do note that I've picked the points that I found the most interesting, leaving a lot out.

We have a sample of one modern human civilization, but there are some hints on how likely it was to happen.

Major types of hints are:

• Time - if something happened extremely quickly; or extremely late, it suggests how likely it was.
• Independent invention - something that was invented independently multiple times is likelier; something invented only once in spite of plenty of time, isolation, and prerequisites is less likely.

Data for:

Related to: Joy in the Merely Real, How An Algorithm Feels From Inside, "Science" As Curiosity-Stopper

Your friend tells you that a certain rock formation on Mars looks a lot like a pyramid, and that maybe it was built by aliens in the distant past. You scoff, and respond that a lot of geological processes can produce regular-looking rocks, and in all the other cases like this closer investigation has revealed the rocks to be completely natural. You think this whole conversation is silly and don't want to waste your time on such nonsense. Your friend scoffs and asks:

"Where's your sense of mystery?"

You respond, as you have been taught to do, that your sense of mystery is exactly where it should be, among all of the real non-flimflam mysteries of science. How exactly does photosynthesis happen, what is the relationship between gravity and quantum theory, what is the source of the perturbations in Neptune's orbit? These are the real mysteries, not some bunkum about aliens. And if we cannot learn to take joy in the merely real, our life will be empty indeed.

But do you really believe it?

I loved the Joy in the Merely Real sequence. But it spoke to me because it's one of the things I have the most trouble with. I am the kind of person who would have much more fun reading about the Martian pyramid than about photosynthesis.

And the one shortcoming of Joy in the Merely Real was that it was entirely normative, and not descriptive. It tells me I should reserve my sense of mystery for real science, but doesn't explain why it's so hard to do so, or why most people never even try.

So what is this sense of mystery thing anyway?

by Anna Salamon and Steve Rayhawk (joint authorship)

Related to: Conjuring An Evolution To Serve You, Disguised Queries 

Let’s say you have a bucket full of “instances” (e.g., genes, hypotheses, students, foods), and you want to choose a good one.  You fish around in the bucket, draw out the first 10 instances you find, and pick the instance that scores highest on some selection criterion.

For example, perhaps your selection criterion is “number of polka dots”, and you reach into the bucket pictured below, and you draw out 10 instances.  What do you get?  Assuming some instances have more polka dots than others, you get hypotheses with an above average number of expected polka dots.  The point I want to dwell on, though -- which is obvious when you think about it, but which sheds significant light on everyday phenomena -- is that you don’t get instances that are just high in polka dots.  You get instances are also high in every trait that correlates with having the most polka dots.

For example, in the bucket above, selecting for instances that have many polka dots implies inadvertently selecting for instances that are red.  Selective processes bring tag-alongs, and the specific tag-alongs that you get (redness, in this case) depend on both the trait you’re selecting for, and the bucket from which you’re selecting.

Nearly all cases of useful selection (e.g., evolution, science) would be unable to produce the cool properties they produce (complex order in organisms, truth in theories) if they didn’t have particular, selection-friendly types of buckets, in addition to good selection criteria.  Zoom in carefully enough, and nearly all of the traits one gets by selection can be considered tag-alongs.  Conversely, if you are consciously selecting entities from buckets with a particular aim in view, you may want to consciously safeguard the “selection-friendliness” of the buckets you are using.

Terrence Deacon's The Symbolic Species is the best book I've ever read on the evolution of intelligence.  Deacon somewhat overreaches when he tries to theorize about what our X-factor is; but his exposition of its evolution is first-class.

Deacon makes an excellent case—he has quite persuaded me—that the increased relative size of our frontal cortex, compared to other hominids, is of overwhelming importance in understanding the evolutionary development of humanity.  It's not just a question of increased computing capacity, like adding extra processors onto a cluster; it's a question of what kind of signals dominate, in the brain.

People with Williams Syndrome (caused by deletion of a certain region on chromosome 7) are hypersocial, ultra-gregarious; as children they fail to show a normal fear of adult strangers.  WSers are cognitively impaired on most dimensions, but their verbal abilities are spared or even exaggerated; they often speak early, with complex sentences and large vocabulary, and excellent verbal recall, even if they can never learn to do basic arithmetic.

Deacon makes a case for some Williams Syndrome symptoms coming from a frontal cortex that is relatively too large for a human, with the result that prefrontal signals—including certain social emotions—dominate more than they should.

Followup to:  Humans in Funny Suits

This fallacy gets its name from an ancient sci-fi TV show, which I never saw myself, but was reported to me by a reputable source (some guy at an SF convention).  Anyone knows the exact reference, do leave a comment.

So the good guys are battling the evil aliens.  Occasionally, the good guys have to fly through an asteroid belt.  As we all know, asteroid belts are as crowded as a New York parking lot, so their ship has to carefully dodge the asteroids.  The evil aliens, though, can fly right through the asteroid belt because they have amazing technology that dematerializes their ships, and lets them pass through the asteroids.

Eventually, the good guys capture an evil alien ship, and go exploring inside it.  The captain of the good guys finds the alien bridge, and on the bridge is a lever.  "Ah," says the captain, "this must be the lever that makes the ship dematerialize!"  So he pries up the control lever and carries it back to his ship, after which his ship can also dematerialize.

Similarly, to this day, it is still quite popular to try to program an AI with "semantic networks" that look something like this:

(apple is-a fruit)
(fruit is-a food)
(fruit is-a plant)

Followup to:  Evolutions Are Stupid (But Work Anyway), Evolutionary Psychology

Biological organisms in general, and human brains particularly, contain complex adaptations; adaptations which involve many genes working in concert. Complex adaptations must evolve incrementally, gene by gene.  If gene B depends on gene A to produce its effect, then gene A has to become nearly universal in the gene pool before there's a substantial selection pressure in favor of gene B.

A fur coat isn't an evolutionary advantage unless the environment reliably throws cold weather at you.  And other genes are also part of the environment; they are the genetic environment.  If gene B depends on gene A, then gene B isn't a significant advantage unless gene A is reliably part of the genetic environment.

Let's say that you have a complex adaptation with six interdependent parts, and that each of the six genes is independently at ten percent frequency in the population.  The chance of assembling a whole working adaptation is literally a million to one; and the average fitness of the genes is tiny, and they will not increase in frequency.

In a sexually reproducing species, complex adaptations are necessarily universal.

Followup to:  Rational vs. Scientific Ev-Psych, The Tragedy of Group Selectionism, Evolving to Extinction

Perhaps the real reason that evolutionary "just-so stories" got a bad name is that so many attempted stories are prima facie absurdities to serious students of the field.

As an example, consider a hypothesis I've heard a few times (though I didn't manage to dig up an example).  The one says:  Where does religion come from?  It appears to be a human universal, and to have its own emotion backing it - the emotion of religious faith.  Religion often involves costly sacrifices, even in hunter-gatherer tribes - why does it persist?  What selection pressure could there possibly be for religion?

So, the one concludes, religion must have evolved because it bound tribes closer together, and enabled them to defeat other tribes that didn't have religion.

This, of course, is a group selection argument - an individual sacrifice for a group benefit - and see the referenced posts if you're not familiar with the math, simulations, and observations which show that group selection arguments are extremely difficult to make work.  For example, a 3% individual fitness sacrifice which doubles the fitness of the tribe will fail to rise to universality, even under unrealistically liberal assumptions, if the tribe size is as large as fifty.  Tribes would need to have no more than 5 members if the individual fitness cost were 10%.  You can see at a glance from the sex ratio in human births that, in humans, individual selection pressures overwhelmingly dominate group selection pressures.  This is an example of what I mean by prima facie absurdity.