"My understanding is that there's wide human variation in the level of stimulation needed for happiness." 
 
More important is the large variation in the saliency detectors that convert perceptions into mental focus: the types of stimuli that enthrall people vary widely. Many people with ADD can easily achieve high mental focus for particular activities, including intellectual activities, and not for others. 
 
"The excruciatingly repetitive task of farming must have led to selection for low stimulus people, vice the older and more exciting pursuits of hunting and warfare." 
 
Farming-adapted people have a very high need for stimulus, but their saliency detectors are tuned to hypothetical simulations of future events.  
 
Many farmers can hunt well at carefully selected times, showing that they also have the ability to consciously control their saliency detectors. IMHO this sort of meta-thinking is what distinguishes civilized humans from the wild type.

Ah. I see what you're saying after reading it again when not sleepy. 
 
Goldstein does say "Another possibility, however, is that some of the associations that are credited to common variants are actually synthetic associations involving multiple rare variants that occur, by chance, more frequently in association with one allele at a common SNP than with the other." That is a bit of a reach, but he does not seem dead set on the number of "important" loci being small. 
 
In any event, Cheap Sequencing Now!

"Thus, though a rare polymorphism might have a large effect (in sense 2), it will explain a tiny amount of the variance in the trait simply due to the fact it is rare." 
 
This is true, but it is not Goldstein's point. He is searching for core signaling pathways that can be manipulated by drugs, not doing population statistics. 
 
The easiest way to identify those core pathways is to find variations that confer a severe loss (or gain) of function phenotype with high probability—a large "effect" in his article. And those deleterious variations will almost always be rare, since natural selection usually does not favor common deleterious variations.

Orion42, the Flynn effect is measured at the population level, but it is caused by processes operating on individuals. Those processes are probably gene dependent, so creating the Flynn effect using scarce resources requires genetic targeting. It's a lot more than nutrition, too. Control of parasites and rewiring of developing brains are probably just as important. 
 
"The only non-controversial ethical use I can think of for genetic intelligence testing would be early screening for mental retardation (defined at IQ below 70)." 
 
That's over half the babies in some areas of Africa! There had better be controversy and clear discussion, because a sensible mandatory screening program in Massachusetts would be radical genetic cleansing if applied to certain countries.

(1) You could selective abort fetuses likely to have low IQ. (Judging by the popular reaction to Sarah Palin's trisomy 21 kid, failing to do this already makes you a pariah in some circles.) 
 
(2) If a young child's genes predict he is likely to be susceptible to the Flynn effect, you could give him extra training to try to trigger the effect. This could provide more focused, effective use of education foreign aid in Africa, where general intelligence is desperately needed.

Cities: Humans check in, but they don't check out.

3) Environmental hardship forces migration, simultaneously reducing fertility and the relatedness of potential mates?

"Connecting the dots, it's quite plausible that these particular ancient retroviruses have been recruited into the mammalian genome and serve as local immunosuppressors in the uterus during development. In fact, we already know that syncytin, a protein crucial in placenta formation, is the product of a retroviral gene (Knerr et al. 2004), so there's nothing at all far-fetched about this." 
 
My casual reading says the syncytin question is murky. Syncytin 1 (HERV-W-derived) is active in hominoids but not old world monkeys (Cáceres and Thomas, 2006). ERV-3 (HERV-R) is expressed in the human placenta and has apparent syncytial and immunosuppressive domains, but 1% of Caucasians are fertile despite being natural homozygous knockouts (de Parseval and Heidmann, 1998).

This research found that 0.9% of cells in schizophrenic human brains are aneuploid for chromosome 1, whereas only 0.3% were in normal controls. (Aneuploid == gain or loss of a chromosome.)

"... pumping pregnant sheep full of every anti-viral and anti-bacterial available?" 
 
I would expect significant birth defects or maternal death. Many anti-infection drugs have significant side effects. E.g., the anti-influenza drug amantadine stimulates dopamine receptors. Several antibacterials are broad spectrum antimetabolites (e.g., folic acid antagonists). And sheep are ruminants that rely on gut microbes to digest their food, so you would need either total intravenous nutrition ($1000/day) or a clever diet that has not yet been invented.

are you being serious? 
 
MC1R and/or red hair are also associated with reduced sensitivity to analgesics: 
 
Melanocortin-1 receptor gene variants affect pain and mu-opioid analgesia in mice and humans. 
 
Increased sensitivity to thermal pain and reduced subcutaneous lidocaine efficacy in redheads.

"We know from population genetic theory that such traits have not been subject to powerful directional selection for long periods of time." 
 
But what if there are multiple populations that don't interbreed much? A less variable population would tend to converge to an instinct-driven Tit For Tat-like strategy. A highly-variable population might be forced to use complex cognitive strategies instead, which can converge to more altruistic behaviors than Tit For Tat. The latter groups might therefore tend to conquer or dilute the former groups. (Is there a standard term for this variety-dependent group selection?) 
 
"the range of basal testosterone should be very small and predominantly environmental/non-heritable" 
 
Perhaps not. Various references on the web quote a 5:1 range between males, and a 2:1 daily range for a given male. Also, this reference says that humans have levels of DHEA (neurologically active, testosterone precursor) that are drastically higher than some other mammals, and this reference says chimpanzees share this trait.  
 
Incidentally, human DHEA production turns on in middle childhood, so it is likely much more than a simple reproductive hormone.

I have long thought the opposite: the stability and hospitality of the tropics are what make them so popular with parasites. High-latitude winters are not kind to either vectors or reservoirs.

My comment got out of hand and turned into a blog post of its own.

A typical scam: all noise, no threat. 
 
The claim of copyright infringement is insinuated, not asserted. The copyrighted work is not identified, despite having a standardized citation and DOI. The conditional passive voice ("If these figures are not removed immediately...") deflects personal accountability away from the JW&S employee. The impossible deadline of "immediately" is intended to provoke a defensive reaction in the recipient. The threat is vague "further action", which could mean anything from criminal prosecution to a sound tongue lashing. 
 
Legally-meaningless twaddle. And it worked. The blogger kissed the ass of an Editorial Assistant believing they were a fancy laywer, then bent over backwards to avoid even the appearance of malfeasance. People do silly things when they're afraid. 
 
And the blogger is a neuroscience PhD candidate! Think on that.

"If it isn't obvious why, you can think of an unmeylinated axon as a leaky pipe ..." 
 
With super-stretchy rubber walls, so you have to move great barrels of water in or out to change the pressure. 
 
Myelin's other big purpose is to make the pipe walls stiffer (lower electrical capacitance), so the axon's voltage can be changed by far fewer ions. That gives the axon fast propagation without needing more ion channels than it can afford. 
 
(I suspect capacitance drives myelin's shape and size. I bet evolution could come up with a thinner low-leakage barrier, but physics dictates that the only way to reduce capacitance is a thick layer of big, greasy molecules. It's the same reason we electrical engineers wrap our data wires in a thick layer of hydrocarbon, when a thin layer would suffice to keep charge from leaking away.)

Re. nuclear effects of learning: I expect one thing it does is to prime inhibitory and apototic mechanisms, to prevent a synapse strengthening storm. If so, you would see the same expression changes after epileptic seizure. 
 
"You can attach or detach acetyl groups or methyl groups (or phosphate groups or ubiquitin groups or SUMO groups, histones must look like Katamari Damacy)" 
 
An amusing mental image!

"I'd love to have a way of specifically blocking the methylation of PP1, for example, during the consolidation period. (And I'm open to suggestions for how to achieve this...)" 
 
Idea: bond an appropriate zinc finger protein to a demethylator (or alternatively a methyltransferase antibody).

Bookmarked!

I think it will be difficult to untangle the causes of core metabolic adaptations. Farming not only increased carbohydrate availability, it also substantially changed the nature of metabolic demands by turning people into draft animals, and changed the seasonal ebb and flow of fat cells. If you want to understand adaptation to diet, look at the systems around unique, rare dietary components. Lactase is the famous example. Another one might turn out to be the vitamin C conservation and disposal systems; some diets are close to deficiency, while others are far beyond sufficiency and require active disposal of the excess. 
 
Selection on dopaminergic signaling systems will probably also be informative. They govern not only motivation and planning (fill that stomach now versus save the seed corn for next season's crops) but digestion and metabolism. Dopamine receptor agonists often both brighten mood and cause weight loss, while antagonists are famous for destroying motivation and inducing obesity and insulin resistance.