http://precedings.nature.com/documents/1293/version/2

I can see your point. However, there are some ways you can consider the effects of Trans -Atlantic slave trade to have been long-lasting genetically.

Consider particularly the case of areas like the Caribbean and Brazil, where there was a constant population decline due to a surfeit of women. The likelihood of any male slave successfully reproducing was very low, due to a high death rate, two men for every woman, fraternization between the sexes being frowned upon by many masters in those regions, etc.

The question is what kind of winnowing happened? In the case of the British Caribbean, for example, populations finally stabilized and began growing slightly before or a generation after the end of the slave trade. Whose genes won out? Were the descendents of the modern-day Jamaicans, Barbadians, or Guyanese almost entirely those who were lucky enough to be in the last batches of slaves sent over? Or was there a core native-born population which persisted, but did not grow, for centuries, occasionally leavened on occasion with those new African slaves which were lucky enough to survive? I have to think there was at least some element of the latter, because the women who lived in the islands would be disproportionately likely to be native-born, given how few were shipped there at any given time.

Also, there was a lot of trans-shipment within the New World at times (most famous in the U.S. as being “sold down the river)” A child born in 1820 in the Upper South, for example, had a 30% chance of being sold to an owner in the Deep South by the time they turned 30. Obviously this was on the whole less traumatic, and certainly less life-threatening, than initial enslavement, but I would be highly surprised if it didn’t cause some level of elevated mortality.

From what I’ve read (including 1493, which I’m working through), the Middle Passage didn’t have such a selective effect, but would only have selected for general ability to withstand malnutrition and abuse, which has been intermittently selected for during most of human history and pre-history.

For that matter, while the overall effect was likely more than one generation, much of the pre-1492 American population was subject to a one-generation selective sweep for certain sorts of disease resistance – it would be interesting to compare genes between modern pure-blood American Indians and DNA samples from pre-1492 American Indians.

I’m not sure it’s fair to say the Middle Passage was a one-off event, considering the trans-Atlantic slave trade ran from 1502 to 1859. It was a series of selections, which probably killed 1.2-2.4 million out of the 11-12 million which left on the ships – a mortality rate of roughly 10-20%. This doesn’t even count those who were killed in the process of capture itself, which probably were several times higher. For these individuals, it was a single-generation event, but it was a dramatic winnowing over 18 generations.

And of course, there was the casualty rate in slavery itself. I’ve seen estimates that up to half of people ended up killed in slave raids in Africa (not surprising), and that 15%-50% died during the first year of being a slave (the “seasoning” period). The first was likely a random trauma, but the second probably had a major selective pressure as well.

What about afterward? In the Caribbean, slave population had a net natural decrease of 20-50 per thousand (2%-5%) each year. Brazil had similar rates. The U.S. slave population naturally expanded, but this seems more to due with the practice in British North America of importing women and breeding slaves, not merely buying fresh ones from Africa when the old ones died off. In addition, pregnancies were often discouraged, or very infrequent, in many of the tropical colonies, whilst by the 19th century, the average female U.S. slave had nine children. So different selective processes were likely underway in different countries.

It’s difficult to determine in Africa to what degree their current measured IQ’s (which are often guesstimated) are genetic ceiling because of the artificial lowering via parasite load or malnutrition and whatever, amongst the various populations. I would not expect it to be equivalent. IQ variation amongst white populations can also be significant (which makes me think it would be amongst them too, as it is with east indians and so on) but it’s hard to unpack what is genetic and what is not, and to what degree genes influences the classes. I mean, aren’t Serbians apparently closer (roughly) to African Americans in terms of average IQ than they are to some other white groups? Are working class white boys in the UK cognitively closer to the Afro-Caribbean boys or to their mid/upper class brethren? The answer is not that clear.

As for IQ variation within sub-Saharan Africa, there is some. It looks to be lower in the Bushmen and Pygmies.

“But selection doesn’t just happen on a continental basis.”

Very good point. For one example, Sickle cell disease strictly speaking is NOT a black disease. It’s actually a central/west African disease (and some Arabs and east Indians, I think). What people call black in the US they actually refer the West African “race” and they forget that what is true for them is not necessarily true for black people as a whole.

This was a point I was trying to say. I have no problem with the idea that natural selection may have caused minor variances in intelligence. I’d actually be quite surprised if there’s not at least a 5% average variance from population to population (E.G., I expect at least a third of the IQ gap is genetic, and wouldn’t be surprised if it’s a bit higher). But selection doesn’t just happen on a continental basis. Young men in Portugal are still 6% shorter than young men in Denmark. GDP might be lower in Portugal, but surely the difference isn’t enough that the Portuguese aren’t getting adequate nutrition.

The problem is that the potential selective events are localized to given areas, and shift with time. Climates change. Civilizations rise and fall. One could easily see local selection for intelligence in one region, and then have that selection fall to the wayside a few centuries later. It’s for this reason I feel that the argument “People of sub-Saharan African descent are a are a standard deviation lower due to biological factors” is too much a just-so story, and when we get into the data, we’ll find there’s tremendous variance between different groups.

I wouldn’t be surprised at all, for example, if it was discovered there were statistically significant differences between the intelligence of those who are descendents of the black diaspora, and Africans, which cannot be accounted for by white admixture. Given the sheer number of people who died in the Middle Passage, and due to the process of slavery, diasporic Africans probably have had the most rapid selection process of any group in human history. It could be African blacks have a potential roughly equal to those of other continents (with the Flynn Effect making modern scores artificially low), but slavery tended to kill off the most intelligent blacks in the New World, who were more likely to attempt to run away or otherwise irk their masters and get sold down the river. Certainly with literacy for slaves made illegal in the U.S. for quite some time there was a big potential punishment for those smart enough to figure out literacy on their own. Surely being forced for generations to do back-breaking labor for centuries (with not even the few escape valves that peasants in Europe occasionally had), could have caused selective pressure as well, not just in terms of physical stamina, but in terms of cognitive processes.

Some of today’s ethnic groups are recent constructions of nationalism (many people had no ethnicity before nationalism), while some have existed since already before the emergence of nationalism. So each ethnic group should be evaluated individually.

I think we’ve always known and still basically know (even if more implicitly) what is obvious: that people are different. There is just the fear of this idea being leveraged for political purposes, which is unfortunate but how it is, as there are people even now strongly vested in doing just that (on both sides of the fence there is agenda though). It seems people struggle to keep this a purely scientific pursuit, even on the part of some of the intelligence researchers, I might add.

Do we really think this is the last unpleasant hypothesis the universe is going to face us with keep rubbing more and more evidence and problems in our faces until we deal with them?

If our species where a bunch of adults this would be a very simple matter to ascertain the truth of. But freaking status signalling, rent seeking, coalition building and damn politicking is keeping us in the dunce corner.

Now, coordination really is hard, but damn people, damn! How incredibly insane we all are.

I suggest you examine the writings of Arthur Jensen. No one is more scrupulous about qualifying his assertions regarding the differing distributions of traits across races than he.

It hasn’t exactly spared him a lot of scorn.