Saying that there is no reason to believe different traits would have the same distribution across vastly different populations is strange. This should not happen even if there were no time for new adaptations to be created (by sheer random chance of copying errors) as the rest of the human population came from a small branch of Africans and does not have the genetic diversity of the continent, for example. Then there are things like the estimated 3% admixture with neaderthals which might have done something.
Intelligence has equal survival value in any climate therefore we should see the same general cognitive capacity within the population of any species.
There are ecosystems where primitive human and primate species managed to survive far before modern levels of intelligence. Now, they have other capacities and advantages over modern humans, but the fact that we still have chimps and monkeys around means that, due to the costs, intelligence in those environments is not a overwhelming advantage until very recently (where we gained ability to wipe them out). There are other environments where no other primate could hope to survive in without a large brain and advanced technology. No primate without the intelligence to maintain the extremely sophisticated technology of the inuit could populate in the artic circle. (without millions of years of new genetic adaptions at least) It is obvious that the survival value for intelligence is not the same for different ecosystems, though it is harder to say the same about reproductive advantages of intelligence which is what we care about in evolution.
Think about it this way: in a distant part of history there was a common ancestor to monkeys and humans. Obviously there was something that caused intelligence and other traits to differentiate over time (and environments) within that species which eventually resulted in new species branches with different intelligence. If we take your claim at face value, this can not happen and everything should be as intelligence as the first cell on the planet that is the source of all life.
The brain is also not a single functioned (general intelligence) abstract aphysical object.
The brain have many specialized functions that take place specific, physical, part of the mind. It does things like processing sensory input, coordinating movement, processing social stimulus (mirror neurons), act out instinctive behaviours, memory of various kinds and such on top of "not that generalized intelligence of IQ". If we look at
http://en.wikipedia.org/wiki/Moravec%27s_paradox it is obvious the most developed and powerful mental capacities are the kind of thing that is considered utterly banal. Those capacities are also developed naturally with only very minimum outside training and must be largely genetic, as it is in other animals. The brain is also a big organ (which makes childbirth difficult for humans) and consume vast amounts of energy and every bit of capacity in those skills is not free.
When a environment is applying selection pressure, it is not selecting for "your brain works or not" but each of those mental abilities individually. If there is a gene variant that could improve one's ability to throw a spear accurately versus differentiating sounds, it obviously would be selected differently in different environments.
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While the genetics of intelligence is extremely complicated, probably the most complicated thing on earth since we don't understand intelligence very well, personality don't require such complexity to change. Look at all the mind altering substances available today, which works like "fixing computers by short circuiting" and is extremely crude, yet have real effects on functioning. Something like serotonin, dopamine, noradrenaline, oxytocin, testosterone levels have important effects on behaviour and is so simple to change via genetics and it would be impossible for biological variation to not exist. Tests showing on heritability of traits exists, and drug trials shows diversity amongst brain chemistry is common.
There's no reason for a population to lose certain abilities of the mind any more than they would lose their sight or hearing because they live in a different part of the world.
It can simply be an accident. Consider events like
http://www.oliversacks.com/books/island ... olorblind/ where a local population do not have capacity to see a certain color because the original settlers just happens to be color blind as the functioning color gene did not exist there, granted a rather extreme case.
That said, loss of function is not uncommon when the selection pressure stopped, like human ability to synthesize vitamin C
http://www.ncbi.nlm.nih.gov/pubmed/22294879. For many animals, ability to see is lost when they moved into environment that no longer require it, like in deep caves.
http://www.biomedcentral.com/1741-7007/10/108/abstract Adaptations is a "use it or lose it" thing.
Richardson's point is that humans have the ability to adapt to their surroundings due to unique evolutionary pressures that impacted our species which makes the need for natural selection to help advance a population's success unnecessary.
We are not yet brains in a tank that moves things by ESP. Human intelligence, as powerful as it is, can only do so much. It does not help if you are a Native America and has the misfortune of contacting the human weapon of mass destruction that is Europeans who carrys disease that will kill you with 90% certainty. It does not help in case of crop failure and you simply do not have enough body fat to last till the next year. It does not help if you a large, about equally intelligent guy decides to poke you with a sword. It does not help you if the environment you live in is heavily lacking in oxygen, and so and so on.
Consider the different pressures. There are hard filters like disease that if you lack genetic resistence of very modern medical treatment (hardly one century old), you will likely die. There are also weaker selection pressures, where you might survive, but another person that is more suitable for the environment will reproduce more and alter the genetic distribution.
If we are talking about mental capacity, I see quite a few traits like being white while living in the tropics: sure you'll get quite dark in the end and adapted to the environment, but probably never as quite as dark as those born black, and you'll get sunburned quite a bit before you adapt, and will have elevated chance of skin cancer over your lifespan, a obvious disadvantage.
The quoted line of thinking is just a extreme form of human exceptionalism that I can not accept. Mental flexbility is expensive anyways since it means more time needed to learn stuff. If one could hardcode useful skills, one could become effective and functional far faster, and examples of specialized function of the brain is example of it.
It is only in the last 2 century where population growth have become untethered from nature pressures. It is also so short of a time that the genetic legacy of previous selection events easily remain.
We might but the real issue is whether those difference are rooted in genetics as racists assert.
Intelligence and other mental traits is genetic:
Take IQ
http://blogs.discovermagazine.com/gnxp/ ... QsFnnaOWJM
http://en.wikipedia.org/wiki/Phenylketonuria <--- granted harmful mutations of this severity is quickly removed by nature selection, but in the chart below you can indeed see a difference in distribution
Take mental illness
http://en.wikipedia.org/wiki/Heritability_of_autism
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Now there may or may not be group differences, but difference in ability due to genetics is well established.
What I oppose when it comes to racialism is the idea that nature has created differences between humans that result in large groups having less potential to succeed than other groups implying that their is a limit to one's ability to learn because of their recent continental ancestry. I know of no credible test which has demonstrated for instance that a person of majority Sub-Saharan African ancestry with physical characteristics that are commonly labeled as "Black" can't have occupation X because they're simply not smart enough.
I agree, race is far too loose a test and not conclusive since correlations proves nothing. We can do better now. In the not too far future when the genetics of mental traits is sorted out, we'd have tests tell you, EXACTLY how much potential you have as a INDIVIDUAL to succeed in your particular set of genes.
I think it'd make the problems of racism (even racists are not "that racists" compared to what powerful scientific discrimination can make perfectly reasonable people do) look tiny.