July 17, 2012

Things Fall Apart: Greg Cochran's new theory of the cause of racial differences in IQ

Over at West Hunter, Greg Cochran has been introducing a a fairly new and potentially important theory of the genetic origins of race differences in IQ.  It's less a theory of evolution than of devolution. The mechanism causing effective differences, he argues, is less selection for higher IQ due to differences in the environment (e.g., winter versus tropics selecting for forethought); instead, a large driver is differential rates in random mutation leading to differences in average level of deleterious genetic load, which tend to correlate with climate warmth.
Sanctuary 
What would happen if people moved somewhere where the mutation rate was far lower? 
Their genetic load would decrease with time, assuming that they were still subject to much selection. Today, everybody has hundreds of nicked or broken genes:  selection keeps eliminating them, while mutation keeps creating them.  The suspicion is that their effect is quite large.  This hypothetical population would have fewer and fewer.  In a few thousand years, they would lose most of the variants that decrease fitness by 1% or more.

Cochran's next post looks at some data on the rates at which random mutations creep into the reproduction process.
Too Darn Hot? 
Posted on July 14, 2012 by gcochran9 
Several recent papers  give me the impression that there is regional variation in mutational load.   One can slice this a number of ways. Dan MacArthur and company looked for mutations that knocked out genes – loss-of-function or LOF mutations.  Mutational load is the sum of all deleterious mutations – LOF mutations are a clear-cut subset of total mutational load. 
Some of the LOF mutations they are found are common, and are presumably neutral, maybe even beneficial, but most are rare and likely deleterious.  The kicker is that they found significantly more LOF mutations in their African population sample than in their European and East Asian samples – 25% higher.  That was unexpected. 
Population history (and mutation rate) determine the variation you expect to find in neutral genes, but significantly deleterious mutations should be in mutation-selection balance.  A neutral variant might easily be a million years old, but a deleterious variant will  last, on average, 1/s generations, when s is the decrease in fitness caused by that variant.  A mutation that decreases fitness by 1% should disappear in  100 generations or so, about 2500 years.  Ancient bottlenecks should not influence the frequency of such noticeably deleterious mutations. 
Another related paper, by Jacob Tenessen et al,  looked at a large set of coding genes, sequencing many times (average depth of 111x)  for high accuracy. As in in MacArthur’s paper they found that the average person carries many probably-deleterious mutations, mutations which are individually rare.  Each person carried, on average, mutations expected to change function (almost always for the worse, although usually only a little for the worse)  in 313 genes (out of the 15,585 they studied. 
They looked at African-Americans and Americans of European descent, about a thousand of each.  They saw what MacArthur’s group did: there were significantly more probably-deleterious mutations in the 80%-African population.  When they used a loose definition of functional variation, about 20% more : with a more conservative definition,  which should have a higher fraction of truly deleterious genes, about 29% more. 
...    The only simple explanation (that I can think of)  is a higher mutation rate.

One possibility is that heat tends to cause a higher mutation rate.

Henry Harpending then summed up:
Pre-term Births 
Posted on July 16, 2012 by harpend= 
The model that Greg is dancing around suggests (1) that there is variation in mutation rate dependent on temperature or something correlated with temperature, (2) higher mutation rates cause a higher genetic burden in human populations, (3) leading to IQ reduction and other minor dings

Here's my model of this theory (which is probably pretty woozy):

Imagine, say, a factory that builds a complex product, such as a car, according to a complicated set of instructions. But, the instructions on how to build the next car are passed on via the Game of Telephone, with mistakes inevitably creeping in. Sometimes, big mistakes are made, and the resulting car is such a disaster that it can't function at all and has to be scrapped. But, most of the individual mistakes are minor and just mean, say, that instead of delivering 268 horsepower, the engine generates 267. Over time, the Telephone Game build up mistakes until a car is completely unusable and has to be scrapped. At that point the workers go find a better car and get the instructions for that car relayed to them. So, on average, most cars don't come off the assembly line performing at spec, but they perform well enough to make it through a test drive. 

Now imagine two factories making the same car from roughly the same overall design. One is in Nagoya and the other in Lagos. It's so hot and humid alla the time in Nigeria, unfortunately, that the workers get distracted during their Game of Telephone and have a higher rate of errors when transmitting plans from one generation to the next. 

In the comments, commenter extraordinaire Jason Malloy writes:
See these posts from February and April for the conceptual background. 
While not fully or explicitly articulated, this is the first New Big Theory of race differences in quite a while, and an interesting alternative to the reigning sociobiological models available since the 1980s. In the latter models intelligence and reproductive differences are seen as consequences of natural selection in divergent latitudes, but this new model replaces natural selection with accumulated mutational burdens. The differences at lower latitudes are not selectively advantageous, but dysfunctional. 
Dr. Cochran notes that complex adaptive systems, involving the functioning of many genes, should be the most vulnerable to genetic load, so this would obviously be the brain and probably reproductive physiology. So in addition to higher general mortality, dysfunctions associated with mutational burdens might include: 
Mental
- Lower intelligence
- Higher retardation
- Higher mental illness 
Reproductive
- Lower birthweight
- Higher premature births
- Higher infertility
- Higher reproductive deformities
- Higher miscarriage (and general obstetric complications)
- Lower sperm quality 
Of course there is a difference between establishing population differences in genetic load, and proving that this is related to population differences in socially valued traits. I’m not sold on this as a replacement for sociobiological models, although there are aspects that make it useful and attractive in different ways. For example, I recently found that ethnic differences in rate of homosexuality are inversely correlated with latitude. Since theories of selectively advantageous homosexuality fall flat, this theory seemed like a better fit.

In the comments to Henry's post, I offer a couple of tentative criticisms, which you can read there.

74 comments:

Anonymous said...

Whatever the answer may be, there ARE real differences in the races of the world.

anony-mouse said...

This sounds a bit like shoehorning modern observations into very little historical evidence.

Are the Inuit roughly as intelligent as the Scandinavians? I don't think so.

For most of Western civilisation you could assume that Mediterraneans were more intelligent than Nordics-and Nordics had the advantage of lactose tolerance (and the Aztecs had possibly the most advanced pre-Colombian Amerindian civilisation).

The Mongols and the Koreans don't seem to be far more intelligent than the Cantonese.

Anonymous said...

One also has to remember that those who made it out of Africa are a small subset of Africans, probably selected for extreme fitness. It is no secret that genetic variation on the African continent is much higher than anywhere else; it makes sense that the main reason for more homogeneity in Europe and Asia is this "founder effect".

Surely this has a bearing on these data?

Anon.

Anonymous said...

Lower intelligence
Higher retardation
Higher mental illness


Higher mental illness with higher neurotypicality at the same time, and higher intolerance for neuroAtypicality in others?

Anonymous said...

The theory isn't very good, because:

1 - In spite of those deleterious mutations Blacks are better than Whites at sprinting, jumping, dancing.
2 - In spite of living in a much warmer climate North Italians are smarter than Eskimos.
3 - Theories must to be weighted against competing ones and R/K selection theory already explains most racial differences very well.

Anonymous said...

global warming gonna make us dumber.

Anonymous said...

Isn't the temperature where the DNA is stored around 98.6F regardless of outside temperature? I'm sure somebody has though of that but it seemed an obvious question.

Anonymous said...

I've got to agree with the comment above. If deleterious genetic load reduces IQ, why isn't also associated with physical infirmities?

Anonymous said...

Maybe its not heat but disease burden. Would a higher mutation rate keep a population one step ahead of evolving viruses o'plenty?

Anonymous said...

Link to the latitude homosexuality ethnicity deal please. Or finish the post on it you have to be working on.

Hero said...

Its nice to spin theories, but where is the evidence that this has anything to do with heat?

Humans are pretty good at thermoregulation. If it were due to heat, we should also see this effect in other organisms as well. In fact more so, as they generally have to suffer more from the whims of nature. To my knowledge, we don't see this in other organisms or no one has reported it. Someone could do a thorough lit search on PubMed...

A heat related hypothesis- maybe the greater exposure to solar radiation at the equator, and more time spent in the sun?

What about the possibility that most of sub-Saharan Africa is third world? The people there are more likely to live and die in the same village they were born, and this has likely been the case compared to most people of other races. Granted there are exceptions, but we are talking generalities here. Also, living in a third world environment could expose one to more mutagens perhaps- radon from stone buildings, few regulations about factories dumping god knows what into the rivers, etc.

Perhaps another reason- a third world environment is harsher. Maybe a higher mutation rate is beneficial there- more things to harm you- malaria, war, etc so more likely that natural selection is cutting heavier there.

Anyway, the point is we can hypothesize lots of reasons- lets not assume this is heat, without evidence.

Anonymous said...

A more forgiving environment would "allow" more genetic deterioration to persist for longer.

Warmer climates are in general more forgiving than very cold ones.

Anon.

Anonymous said...

anony-mouse:"(and the Aztecs had possibly the most advanced pre-Colombian Amerindian civilisation)."

Historians do share that opinion.

Syon

Olave d'Estienne said...

Are the Inuit roughly as intelligent as the Scandinavians? I don't think so.... The Mongols and the Koreans don't seem to be far more intelligent than the Cantonese.

Cochran's theory isn't supposed to account for all IQ differences, just the elephant in the room. Europe, sub-Saharan Africa, and East Asia are all dotted with areas of high population density. So why hasn't cognitive sorting (a la Murray & Herrnstein) led to a highly intelligent, creative class in sSA that could have led the continent into the Renaissance? Cochran offers an answer.

Mongols and Inuits live in very low-population areas where cognitive sorting is limited, perhaps even crippled. IIRC Canton was settled heavily by Han from the north.

1 - In spite of those deleterious mutations Blacks are better than Whites at sprinting, jumping, dancing.
2 - In spite of living in a much warmer climate North Italians are smarter than Eskimos.
3 - Theories must to be weighted against competing ones and R/K selection theory already explains most racial differences very well.


1. All negative mutations are weeded out, not necessarily at the same rate. Africa weeds out slow and clumsy people faster than it does dim people. Plausible? I think so. The quickest way nature weeds out dim people is with predictable (cyclic) famines and hypothermia. Unpredictable famines, snake bites, stampedes, and homicides kill smart and dim alike. I cannot prove this but I cannot see much of a problem with it either.

2. The Mediterranean prevented too much interbreeding between Italy and Africa prior to the era of Islamic piracy. In contrast, invasions from the north provided a lot of new blood to Italy. Perhaps a big northern head and a good southern diet are ideal? Only speculating.

If we posit the 21st Parallels as the bounds of the hot mutation zone, almost all of Africa is close to that zone, but the Sahara cuts of North Africa (including Egypt) from the mutants. Similarly the South China Sea cuts off China from e.g. New Guinea. Nothing similar cuts off the Cape from the Congo; sheer distance provides a gradient rather than a boundary.

3. I agree totally. r/K-selection is hard to beat but this theory may fit in somewhere. Why exactly wasn't Africa suited, over the past several millenia, to K-selected people? Perhaps your species has to r-select to deal with excessive numbers of unviable offspring.

Isn't the temperature where the DNA is stored around 98.6F regardless of outside temperature?

I got the impression that Cochran was using temperature as a proxy for amount of sunlight. (You can't use number of sunny days because that doesn't take intensity into account.)

That's all just my guesswork; I hope Cochran will clear this up.

Anonymous said...

Cats from cold climates are bigger and furrier and much calmer than tropical cats. They don't seem more intelligent however. If anything their slow and plodding personality makes them seem otherwise.

With human beings, high intelligence seems to have arisen with urbanization, in particular with the Greeks whose high quality nutrient dense fish and olive diet might have been the first to support a large urban population.

Luke Lea said...

I don't think you'll find this difference between northern and southern China. Not sure though.

Whiskey said...

Cochran has to ignore the obvious heavy selection particularly since the 800's in Europe (moldboard plow, more food resources) for more and more intelligence to get ... FOOD.

The driving thing in places that are cold but are not snowed in all year round and have SOME growing seasons is that populations are always in precarious balance with food supplies.

Unlike say the Inuit, Northern Europeans have all sorts of ways of using technology crucially dependent on iron and later, steel, to cook, prepare, and store food. Baking, boiling, broiling, stewing, frying, steaming, Europeans do it all. As do the Northern Chinese. All to get those scarce calories, before industrialization made them cheap.

Unlike the tropics, where not much complex operations need to be done at the individual level, Northern Europe is characterized by enormous efforts down to the individual family to always try and get more ... FOOD. By fishing, in often brutal cold weather in hostile seas (better boats and ships); by trading wool (White gold in the Middle Ages) for food, or wool textiles (value added) for better food, or processing wheat and barley into beer, bread, such. Or distilling it into ... WHISKEY I might add.

Its always been food, food, food. The Aztecs and surrounding Nahuatl according to first hand accounts did not have a great deal of developed agriculture, their desire for meat may explain the widespread cannibalism (and also eating dogs which are better employed as working animals) found by the Conquistadors -- ALL the Nahuatl and surrounding Indians practiced that, not just the Aztecs.

Eric said...

Since theories of selectively advantageous homosexuality fall flat...

Do they? I find the gay uncle theory pretty persuasive.

Eric said...

It's so hot and humid alla the time in Nigeria, unfortunately, that the workers get distracted during their Game of Telephone and have a higher rate of errors when transmitting plans from one generation to the next.

But every once in awhile the workers in Lagos are going to make a car with cool new features you can't get in Nagoya, and that's going to end up being the most popular car, right? Some mutations will end up being beneficial.

I don't see how this works unless intelligence isn't preferentially selected. Otherwise the fast-mutating Africans would be much more intelligent than their Asian and European cousins. What am I missing here?

NOTA said...

I think anon, above, makes a good point: blacks aren't shorter, slower, or weaker than whites, overall, right? If they were living with some widespread loss of functions across the board, I'd expect us to see blacks be outstanding athletes no more often than they're outstanding scientists. Instead, you see the opposite--in a whole bunch of sports, blacks do extremely well, often out of proportion to their numbers. It seems a little fuzzier, but there are also a lot of very talented blacks in entertainment and show business and politics. Again, if we were looking at a population that had across the board deficits (like the Control Normals in Beyond This Horizon, or like people with Downs Syndrome), it sure doesn't seem like we'd see that. I can't imagine what all goes into being a world-class politician or singer or actor, but all three are extremely hard to do, and yet blacks can hold their own there despite the population IQ differences. Contrast this with math and science fields, where blacks are way underrepresented. And in basketball and track and field, they're overrepresented.

Anonymous said...

@ anon 6:21pm

the human body is "meant" to operate in conditions where it can be air-cooled. many body processes give off heat as a part of operation. there have been several studies and (to keep it simple, as humidity, elevation etc all have impacts) the mid to high 70s are around the top of the air temperature range where air-cooling works as humans prefer.
Hotter than that, the body undergoes all kinds of changes. Sweat being the obvious one, so we'll stick with it. The functional unit of "work" in a human is ATP. So, a human in lagos is using ATP to keep his genes @ 98.6, whereas a human in London is using nothing at all. Any time you "do work", you run the risk of distortions. The more ATP you use, and the more systems you use it across, the more fractional distortions you run. Sailer's model of telephone is apt. Lagos, where keeping genes @ 98.6 requires energy, is playing telephone where the lights flicker on and off, the street-noise is loud and it's in your second language. London, whihc requires no "work" to keep the genes in the sweet spot, is telephone w/o distractions

rec1man said...

For the past 10 years, the world men's chess champion is Vish Anand, and his ancestors have been living in the very hot Kaveri delta in South India for 1000 years.

However there could be something to the disease burden angle.

His caste, had extreme rules for ritual cleanliness.

Marlo said...

Race differences in IQ are a result of Whites and Asians doing it with Neanderthals and Blacks doing it with Heidelbergensis.

Anonymous said...

Finally, Moynihan's Canadian Border Theory vindicated!

If the mutation rate is climate based, how soon would you wait to see a drop in mutation rate if a population moves north? Do African-Americans moving to Michigan have a lower mutation rate after five generations? Do, say, the Inuit or the Finns have a still lower mutation rate? Or Patagonians? Perhaps the mutation rate is in part driven by UV radiation knocking out pieces of DNA?

It seems as though there's a lot of room for quantitative evaluation of the theory.

Simon in London said...

1. China - AIR northern Chinese do score significantly higher on IQ than southern Chinese. They show up quite distinct on DNA maps though, they're not a homogenous population. The Chinese who dominate coastal cities may be mostly north-Chinese, though.

2. If this theory is true it's not human-specific, so we should see different rates of mutational load in other species depending on latitude, and some signs of lower IQ in low-latitude animals.

I suspect that the observation of higher mutational load is correct but that it may not be a significant cause of IQ variation.

If it's true, it would seem to be good news since it would imply that low-latitude populations moving into high latitudes would eventually develop higher IQ.

Anonymous said...

I don't know Steve.
Geneticists tell us that the entire human population can be partitioned neatly into two groupings:
Sub-Saharan Africans
-and-
Everyone else.
The idea seems to be that the bulk of human genetic diveristy lies in sub-saharan Africans. Various theories have been put forward, including genetic 'bottlenecks' form which all non sub-saharans descend. The upshot is that sub-saharans are descended from ancient lineages that others are not - lineages that have been around long enough to pick up more mutations.

Anonymous said...

The 'temperature' hypothesis must be nonsense.

Firstly, the 'optimum operating temperature' for mammalians of the human species is blood heat or 38. 5 deg C (or whatever it is). This is is the temperature that aeons of evolution has made the optimum for the physiological and biological processes of the human body cell to work at. If this temperature was too hot we would have died out millions of years ago. Needless to say, even in the tropics this temperature is rarely exceeded. In temperate climes, it's hardly ever reached - putting mammals that live there at a disadvantage one would think.
Also, we must remember all life evolved in bath-warm tropical seas - this ambient temperature must be the 'best' for cellular processes and chemical reactions, remember all of the cell's main architecture and processes came into being under these conditions - everything that came later was an elaboration. If warm temperatures were deleterious, life would never have got started in the first place.

Kevin B said...

"deleterious variant will last, on average, 1/s generations, when s is the decrease in fitness caused by that variant."

This might be stating something obvious and irrelevant, but I didn't see it addressed so...

Decrease in fitness meaning reproductive success. But all things being equal, reproductive success should be higher in the average climate of tropical Africa because it's a less hostile environment than Europe's climate.

S would have to be modified to take account of environment acting on mortality, so 1/s would modify to 1/ (s/x), where x is an integer representing increasing environmental stress. The same mutation in Africa might not usually kill its bearer, whereas in Europe, during a harsh Winter, it might. In Africa then, the same mutation is passed forward for a much longer period of time.

Mutations would be expected to pile up and be more prevalent amongst Africans because, compared to Europeans, fewer Africans would die (prior to reproductive success) from any given variant.

NOTA said...

Kevin:

Is Sub-Saharan Africa such an easy environment for humans that there's nothing to overcome? (Malaria? Sleeping sickness? Guinea Worms? River Blindness? War? Famine? Cholera?)

Kevin B said...

Not easy. Easier. We're talking of evolutionary time frames so you could make the same assumptions about Europe 2000 years ago, but add in harsh winters.

socks said...

I've also seen Steve Hsu pushing this view.

Anonymous said...

http://www.bloomberg.com/video/roubini-says-2013-storm-may-surpass-2008-crisis-HCAjTp9VTD~gm6Ux8jnQvQ.html

maybe not good to win election and get the blame

Ratan said...

So does this mean that people who use their A/Cs have lower cancer rates than people who don't?

hbd chick said...

@hero - "If it were due to heat, we should also see this effect in other organisms as well. In fact more so, as they generally have to suffer more from the whims of nature. To my knowledge, we don't see this in other organisms or no one has reported it. Someone could do a thorough lit search on PubMed..."

Latitude, elevation and the tempo of molecular evolution in mammals

there's also a bunch of stuff for plants.

Anonymous said...

This new theory is absurd and easily refutable by a few casual observations. Sub-saharan Africans are extremely well adapted compared with Europeans and north Asians in other areas, such as athletic skills, obviously. If Cochran's theory were correct, people living in higher latitudes should also be physiologically more able in these departments as well, which represent a accumulation of molecular order by selection processes in a similar fashion to cognitive advantages. Southern hemisphere humans are well-adapted, only to different environments than Northern hemisphere folk.

sunbeam said...

Another person here to whom this whole thing sounds kind of fishy.

1) How exactly is the temperature difference supposed to cause increased mutations anyway? Physically how does this work?

There is another curious thing these guys say:

"It takes a lot of radiation to double the mutation rate – something like a lethal dose, way more than you get from background radiation in a lifetime."

They've stated this idea several times in places, this particularly quote came from a post where they discuss Heinlein's planet of Sanctuary from Starship Troopers.

This sounds all kind of screwy to me. I can tell you that exposure to elevation CAN elevate your risk for cancer. But this is a kind of complicated topic. There might be some truth to it, but it isn't exactly clear what they mean.

Radiation exposure has been studied extensively, and there is a lot of information to process here.

I can tell you that when Radiation causes cancer, it is because a mutation was induced in a cell. This is an event that is of course analyzed statistically.

Look we could fill up this blog for months with posts debating this subset of what these guys apparently believe. Maybe they know what they are talking about, but it sounds fishy to me.

I could make a guess that there are far more "somatic" cells in the body than those devoted directly to reproduction. It's a low probability event, but cancer well.. grows. On the flip side your testicles are some of the busiest parts of your body, just saying. Lot more going on there that is amenable to ionization.

And to repeat something, how exactly is the relatively minor difference in temperature causing mutations anyway? I mean if I wired up the nuts of a bantu person living in Africa, and some Nordic type living in Sweden, I'm reasonably sure the graphs aren't going to look much different. Maybe I'm wrong, but I'd like to see some physical theory of what they are proposing.

And as others have noted, we are not the only mammals on this planet. It should surely be possible to observe this effect in other species. Has anyone done this?

2) WTF is this genetic noise/mutational load thing? Sure seems like it would be a big deal in biology circles. So why is it not discussed past these guys? I don't keep my eyes peeled for happenings in biology, but is seems kind of strange to me.

3) I love this quote:

"In a simple model, a given mutant has an equilibrium frequency μ/s, when μ is the mutation rate from good to bad alleles and s is the size of the selective disadvantage. To estimate the total impact of mutation at that locus, you multiply the frequency by the expected harm, s: which means that the fitness decrease (from effects at that locus) is just μ, the mutation rate. If we assume that these fitness effects are multiplicative, the total fitness decrease (also called ‘mutational load’) is approximately 1 – exp(-U), when U is where U=Σ2μ, the total number of new harmful mutations per diploid individual."

Sounds all scientific and stuff. Is it just a concept used in thought experiments? Reading their blog it sure seems like quantities are assigned a numeric value for individual mutations.

What is the value of s, expected harm, for color blindness, or the sickle cell gene?

Heck the Pre Term Births post has a graph for god's sake.

I think you could take statistical data and maybe kludge together some values for these theoretical constructs. But you would have to make a lot of assumptions, and you'd argue about the results a long, long time.

And what the hell is a "mutation free individual?"

4) There is a long history of physicists making contributions in many fields. There is also a long history of physicists being ass clowns when they step outside their box.

How do I know these guys know what they are talking about?

Dan said...

I don't buy Cochran's theory at all: humans all have internal temperatures of around 98.6 whether its 25 degrees outside or 100 degrees outside.

Chocran's theory would only be plausible if humans were cold blooded.

Anonymous said...

"Cats from cold climates are bigger and furrier and much calmer than tropical cats. They don't seem more intelligent however. If anything their slow and plodding personality makes them seem otherwise."

You seem to be omitting a natural breed of cat specifically adapted to cold weather, Russian Blue cats. They are probably the most intelligent of felis sylvestris, showing extremely high levels of socialization and adaptive behaviors (craftiness). Breeders have put a lot of pressure on Blues to dumb them down, so as to make them easier to show, but so far without much success.

Dan said...

On the other hand, there is one way that heat could be tied to mutations, indirectly:

A big source of mutations is UV light, right? People in tropical regions endure far higher exposure to UV light, because they wear fewer clothes and because of an overhead sun.

While we are at it, people in the tropics would have a higher exposure to X-rays, gamma rays etc., right?

Anonymous said...

"Do they? I find the gay uncle theory pretty persuasive."

Look around you, here and world wide--see gay men sacrificing for their nieces and nephews survival? Staying home by the hearth and raising EXTRA children (beyond their own genetic offspring) which is what they'd have to do to pay for their evolutionary cost.

One little study of an isolated island came to the conclusion that an effeminate male helped. Fa’afafine? What else to do but what the others do? Womanly chores and the occasional sex fix for a few of the men whose wives are pregnant. They can't exactly run off to the bathhouse or hop a gay cruise.

Anonymous said...

New age of enlightenment.

Dahinda said...

Certain disease rates are higher in warmer climates as well. Do you think that this comes into play?

Dan said...

I have a theory of heat and brain size that hasn't been articulated at all here, even though it is super simple and would explain a lot:

--begin theory--

Since big and busy brains generate a lot more heat, they have put people in grave danger of heatstroke in hot climes.

--end theory--

I'm apparently not the first to have this thought.

http://www.mesacc.edu/dept/d10/asb/origins/bipedality.html

http://www.public.wsu.edu/gened/learn-modules/top_longfor/phychar/02_brain_size.html

http://books.google.com/books?id=NZ19UiDPosEC&pg=PA229&lpg=PA229&dq=heat+stroke+%22brain+size%22&source=bl&ots=BWrbhH3oK7&sig=SKR8J4IPp1QYfQXh2SWFVW5zYU0&hl=en&sa=X&ei=WcoGULDjLYjF6wGxmZHWCA&ved=0CD4Q6AEwAQ#v=onepage&q=heat%20stroke%20%22brain%20size%22&f=false

It makes perfect sense. As a computer science person, I note that processor size and power has always been limited by overheating risk. If you want a supercomputer, you need a cool environment.

And it turns out that cooling systems in the head were an epic part of brain development, meaning that overheating was a huge risk for the brain.

This would explain why arctic people don't have any special advantage over northern Europeans. The risk of heatstroke is trivial in the lands of both.

By these lights, the air conditioner is a *very* important invention.

Anonymous said...

I don't think this is really a new theory. People have talked about hot climes making people dumb/preventing them from becoming smart and the various possible reasons why - mutations, disease, etc. - for a long time.

Anonymous said...

This, you have to see.

HBD, barber shop

http://www.youtube.com/watch?v=9BI2m3QoaS8&feature=plcp

Anonymous said...

"the 'optimum operating temperature' for mammalians of the human species is blood heat or 38. 5 deg C "

not for testicles.

And consider thermophilus

Eric said...

Firstly, the 'optimum operating temperature' for mammalians of the human species is blood heat or 38. 5 deg C (or whatever it is). This is is the temperature that aeons of evolution has made the optimum for the physiological and biological processes of the human body cell to work at. If this temperature was too hot we would have died out millions of years ago. Needless to say, even in the tropics this temperature is rarely exceeded.

You're neglecting the fact that body processes are producing heat under normal conditions. The optimal outside temperature must be cooler than the body's core temperature because otherwise the body has to do something active to dump the excess heat, i.e. sweat.

The fact that humans can survive at 98.6 degrees doesn't mean that's the optimal temperature.

Anonymous said...

Are the Inuit roughly as intelligent as the Scandinavians? I don't think so.

Are the Lapps/Saami, the "European Inuit", as intelligent as the Scandinavians, for that matter?

Anonymous said...

Isn't the temperature where the DNA is stored around 98.6F regardless of outside temperature?

The 'temperature' hypothesis must be nonsense.

Not completely.

Yes, the inner workings of the human body are at 37.05 C (98.6 F) but the body requires energy to maintain that temperature. The ideal outside temperature is 20 C or so - given normal human metabolic activity - because the body needs to expend no extra energy to stay at 37.05 C.

That should mean environments that are too hot or too cold are disadvantageous.

Anonymous said...

Is Sub-Saharan Africa such an easy environment for humans that there's nothing to overcome? (Malaria? Sleeping sickness? Guinea Worms? River Blindness? War? Famine? Cholera?)

Are these things ones that can be overcome with more intelligence, rather than physical toughness and a better immune system?

candid_observer said...

I find this theory puzzling.

Until homo sapiens came on the scene, all of the "more advanced" models of human beings arose not outside of Africa, but from within Africa. These more advanced models supplanted the earlier models no doubt because of superior intelligence.

So why did the most advanced models come from Africa, if the deleterious mutations which damage intelligence are greatest in Africa?

This is of course a more general issue with the claim that colder climates, per se, must be fully responsible in the selection for higher intelligence; there would appear to be other important issues involved.

Also, even granting that more deleterious mutations arise in Africa, why shouldn't more positive ones arise there as well? Why wouldn't they compensate, or more than compensate?

I suppose one might argue that Africa is a better place for major mutations, both positive and negative, and that that's why it was the source of the various models of human beings, but that colder climates are better for incremental, non-revolutionary changes in human intelligence.

But the story would seem to be complex.

Anonymous said...

It's less a theory of evolution than of devolution.

Don't let The Derb hear you say that.

Or Charles Murray, for that matter.

Anonymous said...

"Also, even granting that more deleterious mutations arise in Africa, why shouldn't more positive ones arise there as well? Why wouldn't they compensate, or more than compensate?"

Because good mutations are waaaaaaaay more rare.

Steve Sailer said...

As a commenter pointed out, testicles are perilously external precisely because 98.6 is too warm for production of reliable sperm.

highly_adequate said...

"Because good mutations are waaaaaaaay more rare."

Yeah, but they are vastly more likely to be preserved, right?

Remember: we got here mainly by good mutations, not bad ones, so they better have prevailed over the long run.

candid_observer said...

In a way, this theory strikes me as a bit ironic anyway, because one of the major arguments in The 10,000 Year Explosion for the importance of agriculture in the faster evolution of homo sapiens outside of Africa was that the rate of mutation was much higher in the larger populations enabled by agriculture.

So is the idea now that it's only the bad mutations that are coming in at a faster rate in Africa? I guess I'd like to see a more convincing argument about this.

Dan said...

Overheating is a very, very serious risk for the brain.

http://www.benthamscience.com/cnr/sample/cnr1-1/Kiyatkin.pdf

Dan said...

More on the big-brain heatstroke hypothesis, it seems reasonable that a big and busy brain should be useful everywhere, right? As a commenter pointed out, there is plenty to think about, survival-wise, in Africa. You may not have cold winters, but a dry season brings seasonal starvation too.

If the advantages of a big and busy brain were counterbalanced by big heatstroke risk, it would explain a lot.

jody said...

"One possibility is that heat tends to cause a higher mutation rate."

not heat. photons. there are more photons hitting an organism at the equator than photons hitting an organism at the poles. the sun, a fusion reaction, emits electromagnetic radiation across many spectrums - not all of them make it from the sun to the earth, but one important one does: ultraviolet light in the spectrum from about 200 nm to 400 nm.

and what we know is, radiation causes mutation, so that being exposed to higher intensities of ultraviolet light in the UVA and UVA spectrum causes higher rates of DNA mutation.

warm blooded animals, which humans are, expend energy to maintain temperature. so it's not the heat from the sunlight which would be the hypothesized mechanism. it's the damaging effect of UV spectrum photons.

http://en.wikipedia.org/wiki/Sunlight

UVB to vitamin D synthesis, controlled by latitude:
http://en.wikipedia.org/wiki/Risks_and_benefits_of_sun_exposure

what happens when you get too much UVA and UVB:
http://en.wikipedia.org/wiki/DNA_repair

jody said...

but again, to check this hypothesis, examine all data. what about people at or near the equator who are not africans? are people at similar latitude smarter, dumber, about the same? how do they compare physiologically? psychologically?

also, consider this. UV exposure increases with elevation. according to wikipedia, 4 to 5 percent per 1000 feet is the approximate increase in intensity.

when i go to colorado once a year with a team of guys to run the leadville 100 in the rocky mountains, we peak at 12,000 feet. and you get burned there fast in the summer. it is deceptive, because the air temperature can be 70 degrees, telling your mind from experience, you won't get burned unless you're in direct exposure for hours and hours - but then you get burned after just an hour in direct sunlight with no sunblock.

so again, we have another data point to check against the hypothesis. high altitude dwellers would have more mutations from greater UVA UVB exposure. sea level dwellers would have less. you can even check this within populations for even better experimental control.

jody said...

"In spite of those deleterious mutations Blacks are better than Whites at sprinting, jumping, dancing."

europeans are faster sprinters and better jumpers than anybody except west africans. they run faster, jump higher, and jump further than east africans, north africans, and south africans by decent margin. you can check iaaf.org world track & field rankings if you don't believe this.

africa is a very big continent, people tend to not realize this. the differences between the various people of africa, many of whom look similar because their skin is similar, can be pretty large. almost every "black" competitor in a sprinting or jumping event at the IAAF world class level is a west african. in fact right now, in an olympic year, the best high jumper and long jumper are european. europeans hold most of the south african track & field records in sprinting and jumping, despite being outnumbered 6 to 1, in the nation in africa where the environmental explanation would say the natives are getting the best possible opportunities to succeed in sports.

nevertheless, to address the very real point here, that type IIB muscle fibers are found in higher concentrations and at higher frequency among west africans than any other group, we have to ask ourselves why would genetic instructions for building muscle tissue with type IIA and type I fibers come to predominate as humans moved around africa. indeed, why would IIB become clustered in west africa, drop precipitously in north and east africa, to the point where east africans are terrible athletes, then rise again among europeans, who are stronger than any other group, and faster than any group except west africans.

jody said...

there is no downside to being able to move as quickly as possible, or in the terms of a physicist, generating the highest possible power, or force exerted over time. this is a beneficial morphological arrangement in any environment. there is no downside to being fast, strong, and running and jumping with smooth swiftness. so why did humans lose that moving from west africa to east africa. or, paradoxically, why did humans pick up a different IIB, IIA, I mixture everywhere on earth? which is what we observe in sports science.

so here you have the opposite argument, that a beneficial mutation got ditched when humans entered a lower mutation environment. could it be the lower food, lower calorie, and hence, lower potential energy environment outside of the savannah grasslands of africa, where metabolism of food into fat for energy storage is a critical survival mechanism, which caused the physiology of the human body to change? IIA fibers are energy expensive, and having a IIA fiber ratio of like 50% might not be the right survival trait in all environments.

jody said...

"For example, I recently found that ethnic differences in rate of homosexuality are inversely correlated with latitude."

whoa there man. you found group differences in rate of homosexuality? how? where?

"For the past 10 years, the world men's chess champion is Vish Anand, and his ancestors have been living in the very hot Kaveri delta in South India for 1000 years."

magnus carlsen is the number 1 chess player in the world.

the point stands: dark skinned south asians completely bust all of rushton's hypothesis, and all other HBD hypotheses that human traits are on a sliding scale. like this new greg cochran one. in fact, rushton's most recent work was just posted on vdare and it's...COMPLETELY WRONG.

south asians are almost as dark as most africans, there are over 1 billion of them, so we have tons of data that they are...far less aggressive than some other, fairer groups. less violent, and certainly not muscular or athletic. the same goes for american indians in mexico and other central and south american indians. they just completely bust rushton's hypothesis.

it's because he's not a very good scientist and doesn't check all available data.

Anonymous said...

"Are the Inuit roughly as intelligent as the Scandinavians?"

Yeah, Scans are so smart.

http://www.youtube.com/watch?v=P-Xy-xb4XgM

sunbeam said...

A couple of people have posted about UV.

Just a speculation, but I wonder if the fact that in colder latitudes you wear more clothes might be applicable to anything. Most UV radiation interacts with human bodies at the skin layer, hence the association with skin cancer.

If you aren't wearing clothes, well there is only a thin layer of skin between your testes and UV radiation.

You would kind of expect elevated breast cancer rates too.

Also a couple of people have posted about West Africans and athleticism, at least the kind we stress in American sports, and a lot of Olympic events.

How important was this really? I mean why wasn't Africa conquered by West Africans with lots of fast twitch muscle fiber?

Why wasn't the world for that matter? If not West Africans, some other group with similar adaptations? Why didn't every tribe, everywhere, come to be composed of the descendants of those who were just faster and more explosive in their movements?

Another thing I'm curious about, if anyone knows, is exactly when humanity started living in West Africa. Is it a relatively recent thing as the millenia go? I think man has been in Australia for 50,000 years or so. Is it that long in West Africa?

Also as far as I know, West Africans are the only Africans that seem to have all that fast twitch fiber. I get resistance to disease in that environment, but what was so useful about the fast twitch muscles? Seems like the rest of Africa found endurance more useful.

JI said...

Areas near the equator get more sunshine, which is a form of radiation, some forms of which in turn cause genetic mutations. Just speculating...

TGGP said...

Yes, Rushton made claims in the abstract of a paper which were nowhere supported in the contents.

Subcontinentals seem to be something like "the exception which proves the rule", although their larger total population might mean there is a larger "smart fraction" which is particularly salient (folks in the west don't talk much about peasants in Uttar Pradesh).

tommy said...

r/K selection still sounds much more convincing to me. Direct ultraviolet radiation to a cell could certainly speed the rate of mutagenesis, but how does the sun induce germline mutations and wouldn't evolution move to reduce the rate? And wouldn't an r-selected people be expected to have a wider range of mutations simply by virtue of having more children?

I still think it's more probable that sub-Saharan Africans don't require as much future time orientation as do Europeans and East Asians due to climactic differences, and that this is more likely to account for the known behavioral differences. There are lots of things in premodern sub-Saharan Africa that would kill you, but very few you could easily predict (random famines, epidemics, and animal attacks). Planning your activities around seasons cycling between temperate and cold is another story entirely.

tommy said...

Just a speculation, but I wonder if the fact that in colder latitudes you wear more clothes might be applicable to anything. Most UV radiation interacts with human bodies at the skin layer, hence the association with skin cancer.

That actually brings up another point: higher latitude people should be dumber than those at lower latitudes if UV is responsible. Rates of melanoma tend to be higher not only in sunnier areas but in those at high altitudes due to greater UV penetration. But then, I suppose high altitudes may require more clothing, so maybe not. But then, darker skin should provide greater protection...but...I mean the whole theory is interesting but it just looks questionable.

tommy said...

there is no downside to being able to move as quickly as possible, or in the terms of a physicist, generating the highest possible power, or force exerted over time. this is a beneficial morphological arrangement in any environment. there is no downside to being fast, strong, and running and jumping with smooth swiftness. so why did humans lose that moving from west africa to east africa. or, paradoxically, why did humans pick up a different IIB, IIA, I mixture everywhere on earth? which is what we observe in sports science.

There are definitely trade-offs involved in acceleration, endurance, more muscle mass, etc. when there is only finite energy and resources. Sports cars aren't that fuel efficient after all, nor will they carry as many people as an SUV.

Anonymous said...

"As a computer science person, I note that processor size and power has always been limited by overheating risk."

and that intel has better performance for same power usage.
As a student in northern India, the winters were almost always better academically, a calm attention that was harder to maintain during summer months.
I wonder how much different things might have been if the various entrance tests were conducted during the cool months, say Dec-Feb, instead of the searing heat and loo(and the accompanying maladies) of the months of May-June that had you sweating buckets, with a handkerchief in the free hand, over the answer sheet.

sunbeam said...

"and that intel has better performance for same power usage.
As a student in northern India, the winters were almost always better academically, a calm attention that was harder to maintain during summer months.
I wonder how much different things might have been if the various entrance tests were conducted during the cool months, say Dec-Feb, instead of the searing heat and loo(and the accompanying maladies) of the months of May-June that had you sweating buckets, with a handkerchief in the free hand, over the answer sheet."

I wish this would get investigated. All kinds of things get experiments devoted to them, but I'd like to see this quantified.

It is so hard to think when you have sweat running off yourself and the humidity is through the roof. And the air is just plain nasty to breathe.

I'll always wonder how those bankers wore three piece suits and neckties before we had air conditioning.

Anonymous said...

I wonder how much different things might have been if the various entrance tests were conducted during the cool months, say Dec-Feb, instead of the searing heat and loo(and the accompanying maladies)

Loo maladies = diarrhea?

of the months of May-June that had you sweating buckets, with a handkerchief in the free hand, over the answer sheet.

Anonymous said...

I'll always wonder how those bankers wore three piece suits and neckties before we had air conditioning.

I wonder how those 17th century Croatian mercenaries survived wearing those fancy neckties?