Text

Physicist, Startup Founder, Blogger, Dad

Thursday, December 23, 2010

More ancient DNA

Another ancient hominid (not neanderthals, perhaps one of their contemporaries, or even an earlier erectus variant) appears to have interbred with humans. About 5% of Melanesian DNA appears to come from this hominid, whereas there seems to have been little or no interbreeding with the predecessors of groups such as Europeans, East Asians or Africans. Earlier results showed that modern Eurasians can trace a few percent of their DNA to Neanderthals.

NYTimes, Nature.

So, the following are true:

1. there were wildly divergent ancient hominids (in terms of development, skull shape, physiognomy) who could and did interbreed

2. different groups of modern humans have different distributions of ancient DNA as a consequence of this interbreeding

Much more discussion by Razib at the link below.

gnxp: ... When I was a freshman at university I took a biological anthropology course. The instructor threw out a question to the class. He noted that some paleoanthropologists observed a continuity between the skulls of Australian Aborigines and some Southeast Asian erectine populations. Australian Aborigines are a very robust people, and have been less affected by the trend toward gracility which has been the norm over the past 10,000 years for most human populations. In any case, the instructor asked for a show of hands whether such a possibility should even be discussed openly. The solid majority of the class rejected an open discussion. When asked by the instructor why, many of the students who rejected an examination of the thesis argued that such a possibility opened the path to de-humanization, oppression, and was politically too sensitive. Milford Wolpoff had obviously lost the propaganda war. The students did not consider the possibility of multiregionalism where all human populations exhibited continuity, rather, they assumed that continuity hypothesized for Australian Aborigines was specific to them, and so would associate that population with the less human branches of the hominin tree.

10 comments:

LondonYoung said...

esmith - in one simple model, if the environment were to shift in some way as to create a 1% survival advantage those with allele x, and we assume 25 years per generation, then it would take more than 1700 years for allele x to become merely twice as common. A 10% survival advantage will become 45 times as common in 1000 years assuming it doesn't saturate out in some local region due to lack of human mobility. So, putting aside that mobility concern, we can perhaps bracket how strongly advantageous an allele must be to have come to dominate the global population in 1000 years. Methinks lots of subtle differences can kick around for 10's of thousands of years even if we don't factor in geography.

esmith said...

In medieval Europe, intelligence was correlated with income, and income was strongly correlated with the number of surviving children (to the degree that highest earning individuals could have triple the average number of surviving children vs. poorest peasants). A 10% survival advantage to have an IQ of 110 vs. an IQ of 90 does not seem unreasonable.

As I wrote in a comment here a couple of weeks ago, I think that natural selection for intelligence kicks in above certain level of overall literacy. (Because intelligent people are more likely to be literate, and that provides you with all sorts of further socioeconomic advantages.) None of the European countries had literacy rates in double digits as late as 1600. However, the ones that did get their literacy rates up, ended up doing very well economically.

An illustrative example is Slavic countries. Poles and Bulgarians, for example, share the same genetic history, and even their languages are mutually comprehensible to a large extent, which indicates a common ancestor population that split sometime within the last 1-3 millennia. However, Poles were in close contact with western cultures, some say that Polish deserve the credit from saving the Western civilization from the Ottoman invasion back in the late 17th century. Bulgarians were blocked in by Balkan mountains and they remained largely rural to this day. Outcome? Lynn's national IQ estimate: Poles 99, Bulgarians 93. (Half the black-white gap!) Reading scores on PISA 2009: Poland 500, Bulgaria 429. Median per capita incomes for their respective immigrants to the U.S., as of 1999: $26,418 and $22,903.

LondonYoung said...

Given my math, Power( 1 + advantage, years/25 ), it is hard (for me) to understand how large intelligence gaps can exist in the world if, say, IQ of 110 vs 90 would yield a 10% survival advantage for 1000 years. But, you mention the geographic barriers issue ... I'll add that I also suspect some genes are located close together on stretch of their chromosomes, and that may be playing a role as well (in meiosis, chromosomes are known to prefer to split at only certain points, thus making some alleles "a package deal") ...

LondonYoung said...

I vaguely recall that in England, in the last several centuries, population growth in cities has tended to be negative and thus cities, despite their growth, were population sinks which absorbed people from the countryside. I think something similar is going on in China now. Of course, this wouldn't rule out the idea that cities are the engines of selection pressure for intelligence, but I would think it slows down the process ...

LondonYoung said...

Happy holidays!
What I am thinking is that the agricultural revolutions started 10^4 years ago, so there is still plenty of time left for junky old alleles to have hung on under 1% selection pressure... so, Eurasians could still have more neanderthal stuff hanging around, and Melanesians more of this East Asian hominid stuff hanging around. Give me 10^5 or 10^6 years and I think the differences are gone, but I am not a buyer of homogenization at 10^3 years. But I do think the big advantages spread quickly - like 110 vs 90 IQ. Your old post introduces a very important point about population growth, however. You know, so many of the things we are taught employ ye olde "in steady state" sorta thinking ... and human population, post-agriculture, is not in steady state yet.

esmith said...

I'm afraid that I don't have any citations pro or contra, seeing how IQ was not invented yet. This subject seems to be poorly covered by social science. There is one scientific study (Cochran/Hardy 2005) that deals with intelligence of preindustrial Ashkenazi Jews, and it enunciates an assumption that the medieval correlation between intelligence and income would be the same as that correlation in the U.S. today (which is about 0.4).

I agree that intelligence wouldn't matter for a serf. You need a certain degree of potential for self-realization. On the other hand, serfdom was mostly gone from Western Europe by the 17th century. I probably shouldn't have said 'medieval'. I meant primarily the later period, 1500 to 1900.

esmith said...

So what happens when your hypothetical population gets hit by some real selection pressures?

If there's a bunch of genes that were more common in Neanderthals than in Denisovans, and they give a 0.2% survival advantage for preindustrial farmers and a 10% survival advantage for the 17th century English ... the net effect of this ancient difference should be that the English should take maybe 50 years less under the industrial program till they saturate, vs. preindustrials.

In practice, we're looking at countries that were under the industrial program for 200+ years (most whites) vs. countries that weren't subject to the program at all (sub-Saharan blacks and their African-American descendants).

LondonYoung said...

In my simple formula, big advantages, like 10%, do take over really quickly. In the "Farewell to Alms" kinda world, the English navy carrying English genes around the world is a natural part of that process. But, like with Diamond's Guns and Germs, there are plenty of pockets of people hanging out who seem to defy the model ...

LondonYoung said...

The "rapid takeover" approach would be much more convincing to me if the peoples of northern africa had spread down, around, and through the Sahara bringing selection pressure with them. But this doesn't seem to have happened. So, it makes me think old alleles on the scale of, say, 10's of thousands of years can hang around.

esmith said...

Malthusian trap is not incompatible with selection. Every single animal population in the world is in malthusian trap, yet they manage to select just fine. In the human world, positive selection for intelligence mostly went away with the advent of antibiotics. Only a few 3rd-world, sub-Saharan African countries still have fertility and mortality rates compatible with selection (though not necessarily for intelligence.)

In a perverse kind of way, most 1st-world countries still have selection going on, but nowadays it is the selection AGAINST intelligence, not for intelligence. Because mortality rates are the same for everyone, and birth rates have a strong inverse correlation with intelligence. That's why the US scores have been declining over time compared to other countries. It has a higher degree of diversity and hence a higher degree of selection against intelligence.

What happens in the long run, no one quite knows. Maybe there is a new long-term equilibrium where countries with lower diversity and therefore higher intelligence, like Finland, end up dictating the terms. Maybe we hit the technological singularity and heritable intelligence becomes irrelevant.

Blog Archive

Labels