Very nice summary--thanks.
@SilasBarta:re our careers:
I would certainly never encourage a graduate student to follow up in this area because it would be a career kiss of death. But I am at retirement age, no one is going to fire me, and most important of all I do not have federal grant support. Cochran is not an academic: his real career is in laser physics. So we enjoy a kind of freedom that few academics do.
@JanetK re skin color:
According to standard ag-sci 101 theory the number of loci makes no difference at all to the speed of change of a multi-locus trait. Six is close enough to infinity that skin color should change no faster than, say, IQ. OTOH you may be right in the real world because of the complexities of epistasis of loci.
(EDITED TO ADD: Do not reply to this comment. There is now a top level post for Q&A with the authors of the book which is a better place for you to post your questions than here. The text below is being left "as is" for historical purposes.)
Henry Harpending, one of the authors of the book being reviewed, has already posted a comment here. In order to maximize the value of his attention, I requested and received his permission by email to post this.
The goal is to have a relatively clean "Q&A" grow out of this comment, with interesting child questions posted by members of the community and grandchild answers posted by Henry Harpending or Gregory Cochran which a reader can easily peruse.
If you have any questions for either Harpending or Cochran, please reply to this comment with a question addressed to one or both of them. Material for questions might be derived from their blog for the book which includes stories about hunting animals in Africa with an eye towards evolutionary implications (which rose to my attention based on Steve Sailor's prior attention).
Please do not kibitz in this Q&A... instead go to the kibitzing area to talk about the Q&...
People in agricultural societies, frequently encountering lots of people, are likely to suffer a lot more from being overly aggressive than people in hunter-gatherer societies. Rulers have also always been quick to eliminate those breaking laws or otherwise opposing the current rule, selecting for submissiveness.
On the other hand, submissiveness is surely selected against in rulers, who as noted in the posting leave more descendants than proles. So perhaps in a society in which the strong rule and the weak submit there is some evolutionarily stable distribution along a submissive/aggressive spectrum, rather than favouring one or the other?
Personally, I think that the most relevant variation in humans is the existence of people with Aspergers Syndrome. This is a genuine cognitive difference that makes people with AS have different conceptions of axiology than neurotypicals. Ironically, though Eliezer speaks of the psychological unity of humankind leading to axiological convergence, it is precisely the fact that people with (perhaps mild) AS are more attracted to not compartmentalizing and thinking in terms of a consequentialist morality that has created the singularitarian movement.
After thinking about this I'm not sure AS entails an attraction to consequentialist morality so much as it does an attraction to consistent, axiom-based and systematized theories plus a willingness to ignore (or a lack of) situational and emotional reactions that contradict their systematized view. Consequentialism is just the obvious consistent and systematized view suggested by contemporary post-Enlightenment Western culture. I mean, unless the autism spectrum was empty prior to Bentham it seems likely people with AS were engaged in convoluted theological arguments and Natural law ethics during the middle ages. It is plausible Kant himself had AS. The only difference is that he was ignoring the intuition that it is okay to lie to compliment grandma's poor cooking and to keep a murder from killing your friend where is today, people are ignoring the intuition that it isn't okay to push the guy onto the track to stop a trolley or carve up the homeless guy for his organs.
I'd predict you'd see over-representation of AS among the followers of other contemporary philosophies that are highly consistent and axiom-based but also at odds with majority intuitions: For example, libertarian rights-based morality and Objectivism.
Yes, and I often see stark examples of how this difference in psychology reveals itself. It typically involves a NT joking about the observed behavior of an AS, where the "funny" bit takes the form, "[AS person] performed [action X], when you're OBVIOUSLY supposed to do ~X, though I am completely incapable of saying how ~X inexorably follows as the right one based on typical social experience."
Real example (some details may be off) that's representative of what I see a lot: "Yeah, there's this real weird kid in this class I teach who had read about the Protestant Reformation, but get this -- he actually pronounced it 'pro-TEST-ant'! It was SO funny [because obviously English has a really rigorous orthography that's designed to prevent this kind of thing]!"
I would like to see Eliezer Yudkowsky address the issues raised by NT/AS and by this book, because his position does have a lot of tension with it, even if there's no direct contradiction. (I'm guessing he can dismiss the NT/AS issues a being relatively small in the grand scheme of things.)
It was SO funny [because obviously English has a really rigorous orthography that's designed to prevent this kind of thing]!"
I'm pretty sure that's not how that sort of neurotypical is thinking. It's more like "of course everyone is always alert to get the social details right, and it's shocking incompetence to fall down on the job!".
If so, we're back to psychological unity of the human race-- geeks sneering at people who can't manage to understand completely obvious things about computers are showing the same lack of imagination.
My point was that it's common for people to think of their own skills as normal, and to think it's ridiculous when other people don't have those skills.
The skills may be different, but the assumption that everyone should have at least moderate skill at what comes easy to you is the same.
Perhaps someone could outline the perceived tension in more detail? We already knew humans weren't identical. So just how much variation is how much of a problem for what?
I've picked up some anecdotal evidence for that over the past few months. Just a week ago I was talking with one guy with AS about some ethics problems; he brought up an example where you're with 20 other people, including a baby who won't stop crying, hiding from an approaching army. Under some simplified assumptions, if the baby keeps crying, the army will find and kill all of you, and if the baby stops, they probably won't. If killing the baby is the only way to stop it, is it moral to do so? The consequentialist answer seemed obvious to both of us, even when he specified that the army would spare the baby's life but kill the rest of you. He told me that this is a characteristically autistic way of thinking about moral problems, and he's had more contact with autistic/AS people than I have (aside from being one himself), so I'm inclined to believe him. (I'm not AS myself, but I'm apparently close enough that several people at several points in my life have suspected it, but not enough to be diagnosed with it.)
Edit: He wasn't sure about torture vs. dust specks, but that seemed to be more because he didn't see how a problem involving such impossibly huge numbers of people could have any useful implications about more realistic ethical scenarios. I disagreed — the math is the same, and I think pathological cases are useful for testing the integrity and consistency of ethical theories and for testing how seriously a person takes the theory/methodology they profess to follow — but he didn't find that particular point to be relevant.
Are you sure "flummoxed" is the right word? I don't think "neurotypicals" are confused by the mathematics involved. They just dispute that the utilitarian math represents an accurate theory of ethics. Would you use the word "flummoxed" for a physicist who understands the mathematics of a theory but disputes that it says anything relevant about the real world, even if he has no alternative theory to offer?
For full disclosure, I am not convinced by utilitarian arguments at all, both in these problems you mention and in most other widely disputed ones. I understand them with perfect clarity; I just dispute that they have any relevance beyond the entertainment value of the logical exercise, and possibly propaganda value for some parties in some situations. I certainly wouldn't describe my situation as "flummoxed."
On the other hand, don't forget that talk is cheap, and actions speak louder than words. I doubt that many utilitarians would be willing to follow their conclusions in practice in situations such as the fat man/trolley problem. To stress that point even further, imagine if you had to cut the fat man's throat instead of just pushing him (and feel free to increase the cost of the alternative if you think this changes the equation significantly relative to pushing). I'd bet dollars to donuts that a large majority of the contemporary genteel utilitarians couldn't bring themselves to do it, no matter how clear the calculus that -- according to them -- mandates this course of action.
This suggests to me that this "dumbfoundedness" might be in fact a consequence of more clear and far-reaching insight, not confusion. Biting moral bullets is easy in armchair discussions; what you'd actually be able to bring yourself to do is another question altogether. Therefore, when I see people who coolly affirm the logical conclusions of their favored formal ethical theories even when they run afoul of common folks' intuition, I have to ask if they are really guided by logic to an exceptiona...
The point here is that logical consistency in ethical armchair discussions could in fact be a consequence of myopia, not logical clear-sightedness
You're allowed to say "X is the action I would want to take, but I wouldn't be able to"
This might make sense, but it breaks down the models of pretty much all standard ethical theories, utilitarian and otherwise, which invariably treat humans as unified individuals.
Except for very narrow definitions of "standard," this is just incorrect. Plato, Hume, Kant, and John Stuart Mill all understood and wrote about the difference between what they thought of as the rational or refined will and the more emotional appetite. Likewise Maimonides, St. Augustine, Epictetus, and a 16th century Taoist scholar whose name I can look up for you if it's actually important. In fact, an enormous part of standard ethics deals with the divergence between what we say is right and what we actually do, and tries to identify ways to help us actually do what we say is right.
The blanket assertion that anything you do without being physically restrained is what you wanted to do under the circumstances is a creature of 20th century free-market economics. While it can be part of a self-consistent moral philosophy (e.g. Ayn Rand's Objectivism), it's hardly a litmus test for sound ethical thinking. On the contrary, we should be deeply suspicious of any moral theory that tells us that whatever we do must be what we wanted to do, because it conveniently justifies a set of actions that we (apparently) find quite easy to carry out. What is easy is not always right.
Interesting. This implies that there are actually two ways of interpreting such moral dilemmas: either as A) "what would you actually do in this situation", or B) "what would be the right thing to do in this situation, regardless of whether you'd actually be capable of doing it".
I've always interpreted the questions as being of type B, but the way you write suggests you're thinking of them as being type A. I wonder how much of the disagreement relating to these questions is caused by differing interpretations.
It's more complicated than that. Most people would say that there are imaginable situations where a certain course of action is right, but they'd be strongly tempted to act differently out of base motives. For example, if you ask a typical person whether it would be right to gain a large amount of money by some sort of cheating, assuming you know for sure there won't be any negative consequences, they'll immediately understand that the question is about what's normatively right, not how they'd be tempted to act. Some very sincere people would probably admit that they might yield to the temptation, even though they consider it wrong.
Now, imagine you're introduced to someone who had the opportunity to cheat a business partner for a million dollars with zero risk of repercussions, but flat-out refused to do so out of sheer moral fiber. You'll immediately perceive this person as trustworthy and desirable to deal with -- a man who acts according to high principles, not base passion and instinct. In contrast, you'd shun and despise him if you heard he'd acted otherwise.
However, let's now compare that with the extreme fat man problem (where you'd have to cut the fat man's throat to aver...
Many neurotypicals I have spoken to will take really extreme positions on the fat man trolley problem, saying that they wouldn't push the fat man off the bridge even if a million people were on the trolley.
Eh, as I've argued before on LW, there are utilitarian, AS-compatible justifications for such a position: specifically, that your heroic act shuffles around the risk profiles of various activities in unpredictable ways, thus limiting the ability of people to manage risks, leading them to waste significant resources (perhaps exceeding the amount that would otherwise save more than a million lives) returning to their preferred risk profile.
The key part:
...By intervening to push someone onto the track, you suddenly and unpredictably shift around the causal structure associated with danger in the world, on top of saving a few lives. Now, people have to worry about more heros drafting sacrificial lambs "like that one guy did a few months ago" and have to go to greater lengths to get the same level of risk.
In other words, all the "prediction difficulty" costs associated with randomly changing the "rules of the game" apply. Just as it's costly to make peo
It' isn't just about being fat while being on a bridge over trolley tracks, of course. It might be a worse world if people generally believed they should take deadly action when they see a utilitarian win.
Autism in general affects four times as many men than women in the general population;
Does this statistic refer only to severe cases of autism that are likely to be noticed and diagnosed whenever they occur, or also to the milder, high-functioning autism spectrum disorders? Because if the latter, I would expect that mildly autistic men are much more likely to be noticed as weird and dysfunctional than women, so this might account for at least a part of the discrepancy in the rate of diagnosis.
The explanation for the greater public prominence (and presumably social acumen) of female autistics is probably similar. In most situations, it's probably harder for autistic men than women to avoid coming off as creepy or ridiculous.
I see the differences between this post and the psychological unity of mankind one is akin to two ships passing in the night - not talking about the same thing. In general the arguments do not contradict each other.
I would like to make a few additions:
1) We cannot compare the speed of change in dogs (or pigeons) with that in wild populations. Mongrel and feral dogs are under selection in their normal environment and without control of their breeding therefore they resemble one another much, much more than do pure bred animals. The tame foxes if freed would return fairly quickly to being foxy. Humans on the other hand have continuously changed the environment in which they live (for say 50,000 years). Therefore the selective pressure is not static. So it is not surprising that new genes can arise and flow through populations. Dogs are not relevant here.
2) Genetics is more complex than algebra. In many cases there is an advantage to having two different alleles and both alleles in double dose are disadvantageous. Genes are duplicated (as a mutation) and then one allele can be conserved while another evolves under selective pressure. There are genes that control the use of groups of...
Sounds neat! Thanks for going to the effort to summarize it!
However, now I'm worried. Your summary indicates that Cochran and Harpending are saying a lot of stuff that suggests a genetic basis for intelligence. How long until their careers are over?
I'm going to nitpick a couple points here.
"There is considerable psychological variance between dog breeds: in 1982-2006, there were 1,110 dog attacks in the US that were attributable to pit bull terriers, but only one attributable to Border collies"
Though pit bull terriers are indeed much more dangerous than collies, it may not be entirely behavioral genetics. Unlike collies, pits are often trained to be aggressive. Pits are also simply much stronger and more resistant to pain than than collies, so their attacks are more difficult to defend against, and thus more likely to cause injury, and thus more likely to be reported.
"A larger population means there's more genetic variance: mutations that had previously occurred every 10,000 years or so were now showing up every 400 years. "
True, but a larger population also means that "genetic sweeps" would take longer, especially given our relatively long life spans. If agricultural humans evolved more rapidly I'd say it was more likely due to new selection pressures that their hunter-gatherer ancestors didn't have.
The relevant uses on LW of the "psychological unity of humankind" concept were:
As evidence of common human axiology, i.e. that there are few truly persistent moral disagreements once some kind of "idealization" like volition extrapolation is applied
As the explanation for why it is hard for us to imagine non-human minds, since all human minds are so similar
As for (1), I think that it is refuted by an argument of Greene and Haidt: human moral architecture is universal in form, but its function is to absorb the local morality in youth, i.e. morality is universal in form but local in content.
As for (2), the cognitive differences that we do in fact see in people around the world are clearly not big enough to make a well-traveled person unsurprised by the concept of a paperclip maximizer.
I checked the Wiki here: http://wiki.lesswrong.com/wiki/Human_universal
"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. "
Right - but look at the premise. Genes have linkage to other genes on the same chromosome - and so their frequencies may be far from independent. The existence of this possibility actually creates a selection pressure for interdependent genes that contribute to an adaptation to migrate towards each other on chromosomes - so they have more chance of being inherited together.
This is a parent for comments about Q&A with the authors of "The 10,000 Year Explosion".
If you have a question for either Harpending or Cochran, please post the question as a response there. If you'd like to talk about the Q&A, this is the place to do it.
It seems to be a fairly trivial observation that all adult men and all women do not share the same underlying psychological machinery - because machinery malfunctions - during development, because of bad genes, and as a result of trama and other pathology - so there are quite a few people who are broken and have missing pieces.
There are, of course, also sex and age differences - if you consider all humans.
I argued against the premise of the "The Psychological Unity of Humankind" essay long ago here: http://alife.co.uk/essays/species_unity/
Great post!
The rise in Ashkenazi intelligence seems to be a combination of interbreeding and a history of being primarily in cognitively challenging occupations.
Or of having very high selection for being able to predict when your neighbors are going to try to kill you again. Or of being the only major group of people not having high selection pressure for skill at war for the past 2000 years, letting traits that give other advantages spread more rapidly.
(I don't think interbreeding can raise a population's intelligence. It can just keep it from dissipating.)
Kaj, regarding dogs: the selection pressure of selective breeding is abnormally high compared to the more stochastic effects of more natural selection pressure. Also, 15,000 years ~= 3000 dog generations, 3000 human generations ~= 60,000 years
"More specifically, they suggest that this could have been caused by interbreeding between "modern" humans and Neanderthals."
Probably bunk, IMO. An entertaining story, but lacking supporting evidence.
Superb review - the book has been lingering on my stack for a while, now I feel I've read 1/2 of it.
Damn, looks like an interesting book! Is it entertainingly written? (Looking for a belated mother's day gift.)
This is a really interesting subject with so many possible theses.
To state the obvious, we are all intellectually very different. And I don't think the difference between now and 40,000 years ago has to be all that significant. The less intelligent half of the population is fully human, obviously, but if everybody were at that level of intelligence, we would quite clearly still be making simple stone tools and living in caves. The difference between now and 40,000 years ago is therefore less than the natural variation in the population we see today. So I d...
If we're looking to find out if humans vary significantly in their psychological phenotypes, why not compare these phenotypes directly rather than appealing to highly shaky evolutionary speculations about genotypes?
(Sure, environmental variation also contributes to phenotypic variation, but we have no reason to believe that the current level of human psychological variation is masked by environmental factors - especially since right now environmental variation is probably at its peak in human history)
I'm sure the NIH would love to fund research comparing cognitive phenotypes of different races! Just remember to budget for nails and a cross in your proposal.
From Science, March 12 2010, p. 1316:
'Elsevier told Charlton [editor of a controversial Elsevier non-peer-reviewed journal that published AIDS denial articles] on 22 January that Medical Hypothesis would have to become a peer-reviewed journal. Potentially controversial papers should receive careful scrutiny, the publisher said, and some topics - including "hypotheses that could be interpreted as supporting racism" - should be off-limits.'
We already knew individuals vary in intelligence and personality, so those examples don't seem to me to provide any new evidence against psychological unity in the sense we've mostly been using it. Does the book give other examples of human psychological differences that might have arisen in the recent past?
Great post. However I would contend that psychological unity of mankind seems more like a minority belief on LW.
It would have been entirely possible that the anatomically modern humans interbred with Neanderthals to some degree, the Neanderthals being a source of additional genetic variance that the modern humans could have benefited from.
Can someone square this hypothesis with my understanding that Africa is the mos genetically diverse place on Earth. It seems like an culture explosion has to have at least as much to do with selection pressure as genetic diversity or else the beneficial genes present in the various African clusters would have spread.
Speaking about "big bang" here, one could extend this parallel to a lesser known fact, that our human genetic diversity is increased every day, every hour. Our "genetic universe" appears to be expanding at an increasing rate. Possibly the cultural also, despite the globalization and global culture, everybody talks about.
What could also be another major point of this interesting book, you have found somewhere in the bookspace.
I request that anupriya28 be excluded from this web site. He/she/it is touting web sites by making fake postings all over the Internet. I guess this is the next thing in spam after bots: fake postings written by people in sweatshops somewhere in the Third World.
What are they paying you, anupriya28? Is pissing in everyone else's soup the only way you can feed yourself?
I'm not a scientist, so I'm looking at the subjects here from a different angle. I've read the Harpending/Cochran book and I've read the book "Born on a Blue Day" by Daniel Tammet, on his Asperger's Syndrome. I wrote an article offering the notion that perhaps we are all somewhere on the autism disorder spectrum: http://pavellas.wordpress.com/2008/05/21/where-are-you-on-the-autism-disorder-spectrum/ Best wishes, Ron Pavellas http://pavellas.com.
I'm not sure that statement is really meaningful in a nontrivial way. If we just consider autism, then there's some opposite end of that spectrum; of course everyone's somewhere on it, but you would expect most people to be at 0, or as near as makes no difference.
This seems a good time to point out that actually, there's now pretty good evidence that that spectrum does not end at neurotypicality, but continues past it to an actual "opposite" of autism - schizophrenia. Assuming this is correct, everyone is indeed somewhere on that spectrum!
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:
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.
They first chapter begins by discussing a number of interesting examples:
The second chapter of the book is devoted to a discussion about the "big bang" in cultural evolution that occured about 30,000 to 40,000 years ago. During that time, people began coming up with technological and social innovations at an unprecedented rate. Cave paintings, sculpture and jewelry starting showing up. Tools made during this period were manufactured using materials hundreds of miles away, when previously they had been manufactured with local materials - implying that some sort of trade or exchange developed. Humans are claimed to have been maybe 100 times as inventive than in earlier times.
The authors argue that this was caused by a biological change: that genetic changes allowed for a cultural development in 40,000 BC that hadn't been possible in 100,000 BC. More specifically, they suggest that this could have been caused by interbreeding between "modern" humans and Neanderthals. Even though Neanderthals are viewed as cognitively less developed than modern humans, archeological evidence suggests that at least up to 100,000 years ago, they weren't seriously behind the modern humans of the time. Neanderthals also had a different way of life, being high-risk, highly cooperative hunters while the anatomically modern humans probably had a mixed diet and were more like modern hunter-gatherers. It is known that ongoing natural selection in two populations can allow for simultaenous exploration of divergent development paths. It would have been entirely possible that the anatomically modern humans interbred with Neanderthals to some degree, the Neanderthals being a source of additional genetic variance that the modern humans could have benefited from.
How would this have happened? In effect, the modern humans would have had their own highly beneficial alleles, in addition to which they'd have picked up the best alleles the Neanderthals had. Out of some 20,000 Neanderthal genes, it's highly likely that at least some of them were worth having. There wasn't much interbreeding, so Neanderthal genes with a neutral or negative effect would have disappeared from the modern human population pretty quickly. On the other hand, a beneficial gene's chance of spreading in the population is two times its fitness advantage. If beneficial genes are every now and then injected to the modern human population, chances are that eventually they will end up spreading to fixation. And indeed, both skeletal and genetic evidence shows signs of Neanderthal genes. There are at least two genes, one regulating brain size that appeared about 37,000 years ago and one playing role in speech that appeared about 42,000 years ago, that could plausibly have contributed to the cultural explosion and which may have come from the Neanderthals.
The third chapter discusses the effect of agriculture, which first appeared 10,000 or so years ago. 60,000 years ago, there were something like a quarter of a million modern humans. 3,000 years ago, thanks to the higher food yields allowed by agriculture, there were 60 million humans. A larger population means there's more genetic variance: mutations that had previously occurred every 10,000 years or so were now showing up every 400 years. The changed living conditions also began to select for different genes. A "gene sweep" is a process where beneficial alleles increase in frequency, "sweeping through" the population until everyone has them. Hundreds of these are still ongoing today. For European and Chinese samples, the sweeps' rate of origination peaked at about 5,000 years ago and at 8,500 years ago for one African sample. While the full functions of these alleles are still not known, it is known that most involve changes in metabolism and digestion, defenses against infectious disease, reproduction, DNA repair, or in the central nervous system.
The development of agriculture led, among other things, to a different mix of foods, frequently less healthy than the one enjoyed by hunter-gatherers. For instance, vitamin D was poorly available in the new diet. However, it is also created by ultraviolet radiation from the sun interacting with our skin. After the development of agriculture, several new mutations showed up that led to people in the areas more distant from the equator having lighter skins. There is also evidence of genes that reduce the negative effects associated with e.g. carbohydrates and alcohol. Today, people descending from populations that haven't farmed as long, like Australian Aborigines and many Amerindians, have a distinctive track record of health problems when exposed to Western diets. DNA retrieved from skeletons indicates that 7,000 to 8,000 years ago, no-one in central and northern Europe had the gene for lactose tolerance. 3,000 years, about 25 percent of people in central Europe had it. Today, about 80 percent of the central and northern European population carries the gene.
The fourth chapter continues to discuss mutations that have spread during the last 10,000 or so years. People in certain areas have more mutations giving them a resistance to malaria than people in others. The human skeleton has become more lightly built, more so in some populations. Skull volume has decreased apparently in all populations: in Europeans it is down 10 percent from the hight point about 20,000 years ago. For some reason, Europeans also have a lot of variety in eye and hair color, whereas most of the rest of the world has dark eyes and dark hair, implying some Europe-specific selective pressure that happened to also affect those.
As for cognitive changes: there are new versions of neurotransmitter receptors and transporters. Several of the alleles have effects on serotonin. There are new, mostly regional, versions of genes that affect brain development: axon growth, synapse formation, formation of the layers of the cerebral cortex, and overall brain growth. Evidence from genes affecting both brain development and muscular strength, as well as our knowledge of the fact that humans in 100,000 BC had stronger muscles than we do have today, suggests that we may have traded off muscle strength for higher intelligence. There are also new versions of genes affecting the inner ear, implying that our hearing may still be adapting to the development of language - or that specific human populations might even be adapting to characteristics of their local languages or language families.
Ruling elites have been known to have far more offspring than those of the lower classes, implying selective pressures may also have been work there. 8 percent of Ireland's male population carries an Y chromosome descending from Niall of the Nine Hostages, a high king of Ireland around AD 400. 16 million men in central Asia are direct descendants of Genghis Khan. Most interestingly, people descended from farmers and the lower classes may be less aggressive and more submissive than others. People in agricultural societies, frequently encountering lots of people, are likely to suffer a lot more from being overly aggressive than people in hunter-gatherer societies. Rulers have also always been quick to eliminate those breaking laws or otherwise opposing the current rule, selecting for submissiveness.
The fifth chapter discusses various ways (trade, warfare, etc.) by which different genes have spread through the human population throughout time. The sixth chapter discusses various historical encounters between humans of different groups. Amerindians were decimated by the diseases Europeans brought with them, but the Europeans were not likewise decimated by American diseases. Many Amerindians have a very low diversity of genes regulating their immune system, while even small populations of Old Worlders have highly diverse versions of these genes. On the other hand, Europeans had for a long time difficulty penetrating into Africa, where the local inhabitants had highly evolved genetic resistances to the local diseases. Also, Indo-European languages might have spread so widely in part because an ancestor protolanguge was spoken by lactose tolerant herders. The ability to keep cattle for their milk and not just their flesh allowed the herders to support larger amounts of population per acre, therefore displacing people without lactose tolerance.
The seventh chapter discusses Ashkenazi Jews, whose average IQ is around 112-115 and who are vastly overrepresented among successful scientists, among other things. However, no single statement of Jews being unusually intelligent is found anywhere in preserved classical literature. In contrast, everyone thought that classical Greeks were unusually clever. The rise in Ashkenazi intelligence seems to be a combination of interbreeding and a history of being primarily in cognitively challenging occupations. The majority of Ashkenazi jews were moneylenders by 1100, and the pattern continued for several centuries. Other Jewish populations, like the ones the living in the Islamic countries, were engaged in a variety of occupations and do not seem to have an above-average intelligence.