History, culture, geography + race I'm going to try and answer questions that I find particularly interesting about a post by David Nierengarten in the comments section below where Godless was introducing Gene Expression.

2) Considering ancient civilizations, why did at least a couple arise in Central American and what about the Ethiopian kingdoms? (if sub-Saharan Africans are so lacking in IQ, how did Ethiopia become a respectable kingdom back in the days?)

Is Ethiopia the only example you can give? Because one can dispute whether Ethiopia can be used to represent sub-Saharan Africa with any accuracy. Ethiopians are phenotypically distinct from the inhabitants of west and south Africa, though there is some overlap with other east Africans, especially Somalis. Genetically, their Y-chromosome lineages show a strong infusion of Caucasoid genes (though their mt-DNA is similar to populations to their south and west). The primary languages of the ruling class of Ethiopia (and neighboring Eritrea) are Amarhic and Tigriyna, both Semitic-like Arabic, Hebrew and the ancient languages of the Near East. Their religion-Ethiopian Orthodoxy, is affiliated with the Coptic Church of Egypt. Their ruling dynasty had a tradition of descent from Hebrew (Solomon) and south Arabian royalty (the Queen of Sheba). Look at the kingdom of Axum and the later Ethiopian dynasties, and you'll see that they look outwards, toward Arabia, Egypt, India and even Byzantium. The relations of the Christian Ethiopians of the highlands with black Africans to their south and east is similar to the relations between Christian Germans and pagan Balts in the 10th to 14th centuries, conquest, slavery and subjugation. Ethiopia might be the exception that proves the rule. It is partly the result of cultural diffusion from southern Arabia, sustained by trade with the civilizations of the Eurasian rim. The decline of Axum was directly connected to the decline of its contact with Byzantium, and one wonders if the Ethiopian Christian state would have survived without European intervention during the 16th century (the Nubian Christians fell to Arab jihadis a century earlier). There were other states in Africa, the Shona empire of Great Zimbabwe being the classic example that is purely indigenous. But as John Read notes in Africa: A Biography, aside from the Ethiopians, sub-Saharan Africa has not on its own produced highly bureaucratic states on the classical civilized model. It has not produced a rich indigenous (rather than stimulated from the outside via Islam as in West Africa) literate tradition to supersede its oral tradition. Decentralized tribal confederations have been the rule, not the exception. Why is this? Climate and geography are compelling reasons. And yet, why did southern India and Sri Lanka, as well as Java, both tropical regions without great navigable rivers, develop advanced civilizations (often earlier than northern Europeans). Cultural diffusion (proximity to culture bearing groups) can be used as an example-but then, Ethiopia has been Christian since the 4th century C.E., but Christianity was introduced into Africa from Europe-indicating how much contact Ethiopians had with other sub-Saharan Africans. The Ethiopian model never spread to the rest of the Africa. So some of us, perhaps with more daring than we ought, wonder if perhaps the confluence of climate and geography, and historical happenstance, has molded the behavioral genetics of most Africans to make them more congenial to decentralized tribalisms than large states predicated on a bureaucratic elite. As to central America, the Mayans and Aztecs (as well as the Incas) had sophisticated civilizations, but I think Jared Diamond's explanations in Guns, Germs and Steel were rather cogent as to why they hadn't developed to the levels of Eurasian cultures. I think that one can assert that the Aztecs and Incas were pre-historic states, at the same level of development as the city-states of Sumer or the proto-Egyptian state in the 4th millennium before Christ.

3) What about addressing the idea that population density and neighboring competition inspires technological development? (you need to outsmart your enemies and also develop things like sewers when your cities grow etc). As North America and sub-Saharan African have had low population densities historically, is this perhaps a reason they didn't have the same development as Europe and Asia? (also why the densest populated areas of Central America and Africa had the most advanced kingdoms in the Mayans/Aztecs and Ethiopians).

Chicken and egg. Do dense populations happen because of innovation, or innovation because of dense population? This question has been asked about the neolithic revolution-was it cause or effect? Dense populations don't always lead to innovation though. Greece was a notoriously anti-natal-and Attica was the least fertile region, but the Golden Age of Athens showed that quality, not quantity matters.

4) Why do black Americans score higher (about 1 SD) than black Africans in IQ tests, when black Americans are mostly (about 88% by genetics) similar to black Africans? Is that degree of white admixture sufficient to raise their IQ scores that much?

OK, well, black Americans are 18% white. I do believe that the IQ tests of black Americans are accurate, there's been a consistent trend for 100 years of a 15 point gap. On the other hand, the IQs of certain African nations seem ridiculously low. The lowest I saw was 59! I think we are seeing the result here of the lack of the Flynn Effect. Bad nutrition and poor educational facilities probably don't help the abstract reasoning capabilities of many people in the developing world. Also, though IQ tests in the United States have been reproduced time and again on different groups by different researchers, I suspect some of the results for certain countries were done under less than ideal research conditions, and reproducing the tests would be difficult because of political considerations and possible danger to the researchers lives.

As an aside, just what markers (if any) distinguish South Asians genetically from East Asians or Caucasians?

Hm. I don't have the links handy, but this is what I've found in my research in trolling through issues of The American Journal of Human Genetics and other publications.

• There is a northwest-southeast gradient in genetic markers, with some of the inhabitants of modern day Pakistan having as much in common with Iranians as they do with other Indians
• There is a small contribution by east Asians via Assam-indicated by the presence of a language related to Mon (Burma) and Cambodian in central India (and the possible introduction of rice agriculture).
• The Y-Chromosome lineages of high-caste Indian men show many similarities with Middle Easterners and Europeans.
• The mt-DNA shows far less similarities with the aforementioned groups, and more with lower-caste Indians.
• So, one can think of South Asians as an amalgam between relative newcomers from the north and west with ancient Eurasian inhabitants and a small number of migrants from east Asia. Some South Asians are probably pretty similar to other Caucasoids, especially higher-caste people and Bollywood film stars, while others (the Dalits and Adivasis or tribals) less so.

I can't speak for Godless, but I don't think genetics explains everything. But, as someone who's read Jared Diamond, Thomas Sowell and David S. Lande, the geographic, climatic, historic and culture reasons have been done to death. But what about behavioral genetics? Can it contribute nothing to our understanding of differences between human populations? The common wisdom is, no. But I want to change that and add it to the mix. For that of course, you're usually called a racist (in public at least). We might seem like all we care about is the implications of genetic differences between populations, but the fact is few are talking about it openly, so someone has to broach the topic. As someone with brown skin, I hope I can fend off accusations of being a baby-Storm Trooper. The IQ shown for India is only like 81-so I'm not going to claim racial superiority over someone (though I like to think of myself as an individual-novel idea, I know). And I do think there are negatives with not taking into account possible biological differences between different peoples. For instance, let's be honest about it, most African cultures place a premium on male sexual prowess to the point of caricature. Most African cultures have strong polygamous traditions. Today, most of Africa is Christian or dominated by a Christian political class, so polygamy is officially frowned upon. But that hasn't changed the behavior of individual men, especially those with income and status. They're taking girlfriends who because they can't be second or third wives and be officially fully supported, have multiple boyfriends who also have other girlfriends. This of course leads to the AIDS epidemic which we're so familiar with. The response of Westerners, liberal and conservative, has been to educate Africans on AIDS. Christianity and the liberal conscious wants African men to be good monogamous husbands. But what if in the context of a million years of co-evolved diseases and prey, African man had to develop a particular mating strategy that tends toward polygamy? And that mating strategy is now having problems accommodating itself to western conventions of proper behavior. Of course, if you assume that humans are only cultural beings, the solution would just be to change the culture, which is what people are trying to do. Now, I'm not saying that there's a behavioral difference, but in the current climate, no one could even consider asking if the problem might not be soluble by simply changing the culture.