I would wager that if an average citizen from Athens of 1000 BC were to appear suddenly among us, he or she would be among the brightest and most intellectually alive of our colleagues and companions, with a good memory, a broad range of ideas, and a clear-sighted view of important issues. Furthermore, I would guess that he or she would be among the most emotionally stable of our friends and colleagues.OK. How so?
Crabtree's argument in a nutshell:
In Part I, he outlines the latest evidence showing that many thousands of genes contribute to human cognitive ability, and that because mutation rates are high (higher than previously believed), any given individual probably carries harmful variants of many of these genes. This is quite possibly true ,and interesting, but by itself it's nothing to do with declining IQ.
In Part II, Crabtree says that during human evolution, all of these genes were under strong selection pressure because any human or proto-human who wasn't smart enough to hunt, fight and survive in the stone age environment, would get eaten by a predator or starve. However, after these hunter-gatherer tribes became settled farming communities (in say 6000 BC), they were no longer so vulnerable, so the less intellectually able could live... and breed... leading to ever-more unintelligence genes.
Now, there's a lot of problems here. Many have said that this is all a bit like eugenics, and indeed it is, but that doesn't necessary mean it's wrong... no, it's wrong because the argument is flawed.
For instance, it's already been pointed out that, even if it recently got easier to stay alive, that doesn't mean it's got easier to get laid lots and have lots of kids; and sexual selection is a powerful force in evolution, perhaps even stronger than survival, and it probably favours higher intelligence.
However, there are other issues.
The idea that hunter-gatherers have especially hard lives is dubious. There's good evidence that life expectancy and health fell when hunter-gatherer societies settled down and got agriculture. Today, survival doesn't exert much of a selective pressure in most parts of the world but life stayed pretty precarious (by modern standards) until at least the 19th century. You could indeed argue that 8,000-odd years of agriculture made us smarter than ever before, and that we're enjoying the benefits . In which case we'd be smarter than someone from 1000 BC, who only had 5,000 years or so.
Crabtree does acknowledge that agriculture changed selection pressures. He suggests that it would have made it more important to be immune to the various diseases that emerged when our population density rose. But this isn't enough - for his argument to work, intelligence would also have needed to become less important with agriculture, and whether that's true is really not clear at all. Maybe it did. Maybe it didn't. There's a prejudice in modern culture against 'ignorant peasants' and 'dumb hicks', but farming is not easy.
Even if we do grant that cognitive evolutionary pressures have eased since 1000 BC, it's not clear that this would make us 'less intelligent'. 'Intelligence' is not one thing. To simplify, it might be that there's a trade-off between 'book smarts' and 'street smarts', and that you used to need the latter to survive. A society in which everyone survives would then allow more people the luxury of being book-smart. Would Einstein or Newton would have made good peasants?
Crabtree's arguments are interesting, but they're entirely speculative. There's just no hard evidence for the decline of intelligence over recent millennia. Since we can't go back in time and do IQ tests, there never will be, although he does suggest an experiment, using genetics, that might be able to check whether there's been a build-up of harmful mutations.
But until then, as he puts it,
in the meantime I’m going to have another beer and watch my favorite rerun of ‘Miami CSI’ (if I can figure out how to work the remote control).
Crabtree, G. (2012). Our fragile intellect. Part II Trends in Genetics DOI: 10.1016/j.tig.2012.10.003 Crabtree, G. (2012). Our fragile intellect. Part I Trends in Genetics DOI: 10.1016/j.tig.2012.10.002
24 comments:
He doesn't even address the Flynn effect, which is particularly shameful given that it was probably first noticed on results from the Stanford-Binet.
No need to travel back in time to find recent hunter gather societies.
LOL. Crabtree is trying to explain that which is not known to be.
Nice post, thanks. What rankled me about the crabtree articles was his inference that the several thousand genes estimated to contribute to intelligence act as links in a chain as opposed to a network. This seemed a) totally ad hoc, and b) ludicrous in light of what we know of gene action. Do you agree?
On the whole I think this was a decent rebuttal. However, I take issue with your saying that sexual selection favors higher intelligence. As can be seen in numerous studies on IQ and fertility rates such as this one,http://www.sciencedirect.com/science/article/pii/S0160289607000244, there is in fact a negative correlation between fertility and IQ.
Conraception, spawk.
In reply to the first 'Anonymous' commenter--
Say what you will about this piece, but he *does* address the Flynn effect:
"Box 1. The Flynn effect
The famous Flynn effect, in which absolute IQ scores increased during the first 50 years after the institution of these tests, seems at first glance to contradict the hypothesis that we are losing our intellectual abilities. However, these changes in IQ scores are probably linked to environmental influences including reduction in lead and other heavy metals used in gasoline and paint and the virtual elimination of hypothyroidism in children due to the widespread use of iodinated salt. These and many other advances in prenatal care and prevention of anoxia during childbirth have clear effects on our average intellectual abilities. In addition, scores on these tests have been shown to correlate well with preschooling and other societal influences instituted during the period over which test scores were compared. Consistent with these hypotheses, the gains recorded are predominantly in the raising of lower scores. However, since about 1985 or 1990 these absolute IQ scores have been dropping in some studies, despite considerable ‘teaching to the test’ as well as the general awareness among children that it is important to score well on the test. Most likely these short-term effects are not genetic because the genetic effects at issue are only likely to operate over hundreds of years, not decades. In addition, Flynn points out that we are not getting more intelligent, but instead we are getting ‘smarter’ at taking the tests because our everyday experiences are becoming more like the tests. This is similar to the way that practicing tennis makes one a better badminton player."
Reading comprehension?
Any analysis of intelligence over time should take into account intestinal parasites. One of the most cost effective methods to improve school performance in developing countries is treating intestinal parasites. Hookworm was endemic in the southern US until about 1950, and it was estimated that the average southerner lost 5 IQ points to hookworm, and the south had the less nasty species of hookworm. (The Rockefeller Foundation spent a lot of money on hookworm eradication and they have an amazing photograph of two cousins about the same age, only one of whom had a heavy hookworm infection and the contrast is amazing.) Chronic malaria infection can also stunt intellectual development. These parasitic diseases are present in hunter-gatherer and agricultural societies. Until recently, they were also quite wide-spread. Many of the Ancient Greeks probably had hookworm when they were children, and probably would have been more intelligent if they hadn't been infected. My point being, the eradication of human parasites leads to a significant increase in intelligence.
L Paul Strait: Yes, he does indeed cover Flynn, Anon #1 is mistaken. I think Flynn is a bit of a red herring here, that's all about the past 100 years or so, and Crabtree's arguments are on a millennial scale.
spawk: As Anonymous says, that's probably due to contraception. Today, the highest IQ people don't have many kids, but that's likely because they have access to condoms, abortions etc.
Until recently, they didn't, and probably had as many kids as everyone else. And likely more surviving offspring, assuming being smart helped you to get food and avoid illness.
He probably suffers from penis envy. I blame Hollywood for those flashy 300, Troy movies. A gladiator would be hit by a car today whereas anyone today time travelled back could change the world back then.
"To simplify, it might be that there's a trade-off between 'book smarts' and 'street smarts'"
That sounds like Sternberg's Triarchic theory, which is not empirically validated. The positive manifold is. http://en.wikipedia.org/wiki/Triarchic_theory_of_intelligence#Challenges
IQ predicts staying out of jail and income. Street smarts.
Also, @spawk. Not only does contraception probably distort the ancestral environment association, which even dysgenics doomsayers like Lynn conclude, the study you linked to correlates national average IQs and national average fertility. That's just bad.
He would have been much more onto something if he had noted that educated Greeks had much less access to writing and reading materials and so often memorized swathes of poetry, with content including history and philosophy. Purely through habit, they might have a better memory than us, that we dont need thanks to books diaries and now computers, phones etc. but nothing to do with genes.
Case in point, The last (known) hunter/gatherer tribe:
The Hadza are remarkably unconcerned about food conservation. When they dig up roots, they leave no part of the plant in place to sprout again. When they harvest honey, the seldom bother to seal the broken honeycomb with mud or a stone, which would encourage the bees to return and make more honey. They may know how to dry or smoke meat, but they tend to avoid the effort. Instead, they live for the present
http://www.ntz.info/gen/b00479.html
Contraception is a plausible explanation, but I doubt that it accounts for the total variance. I think this blog from Gene Expression sums up some relevant research rather nicely: http://www.gnxp.com/blog/2007/04/intercourse-and-intelligence.php
Studies looking at high school students have found that high IQ individuals are less likely that average individuals to have had intercourse, kissed, or engaged in any kind of romantic activity. In particular, it was found that each IQ point above average increased male’s odds of virginity by 2.7% and females by 1.7%. If you look at young adults, the odds of virginity are higher among college students than among non college students. Moreover, the rates of virginity are extremely high at more academically rigorous institutions. Not only that, but a breakdown of students by majors seemed to imply that there is a positive correlation between the difficulty of a major and one’s chance of being a virgin. High IQ people also have fewer premarital partners and high IQ correlates with less sex with in marriage.
Given all of this, I find it highly unlikely that all the variance can be explained by contraceptive use.
As for whether or not high IQ was selected for in the past, I have no idea. I don’t view speculation about past selective pressures as very fruitful as there is often no way to falsify such speculation.
Dr Greg Cochran's critique.
http://westhunt.wordpress.com/2012/11/12/the-golden-age/
***Until recently, they didn't, and probably had as many kids as everyone else. And likely more surviving offspring, assuming being smart helped you to get food and avoid illness.***
Indeed, Steve Hsu notes here examples of the middle class outproducing the poor in China and the Britain (the Greg Clark data from examining wills).
"So we have at least two documented cases of the descendants of the rich replacing the poor over an extended period of time. My guess is that this kind of population dynamics was quite common in the past. (Today we see the opposite pattern!) Could this type of natural selection lead to changes in quantitative, heritable traits over a relatively short period of time?
Consider the following simple model, where X is a heritable trait such as intelligence or conscientiousness or even height. Suppose that X has narrow sense heritability of one half. Divide the population into 3 groups:
Group 1 bottom 1/6 in X; < 1 SD below average
Group 2 middle 2/3 in X; between -1 and +1 SD
Group 3 highest 1/6 in X; > 1 SD above average
Suppose that Group 3 has a reproductive rate which is 10% higher than Group 2, whereas Group 1 reproduces at a 10% lower rate than Group 2. A relatively weak correlation between X and material wealth could produce this effect, given the demographic data above (the rich outreproduced the poor almost 2 to 1!). Now we can calculate the change in population mean for X over a single generation. In units of SDs, the mean changes by roughly 1/6 ( .1 + .1) 1/2 or about .02 SD. (I assumed assortative mating by group.) Thus it would take roughly 50 generations, or 1k years, under such conditions for the population to experience a 1 SD shift in X."
http://infoproc.blogspot.co.nz/2011/08/demography-and-fast-evolution.html
Spawk: Hmm. Modern high schools are evolutionarily novel and weird, though. In the past teenagers were much more integrated into 'real' society & expected to marry earlier... but were only able to do so if they had enough money. So you can see how a high IQ would be beneficial.
On the other hand nowadays teenagers (at least high status ones) are told not to have sex too soon and to work towards their future career. If you assume that the high IQ ones are better able to follow societies demands... maybe it's no surprise they have less sex at a young age.
Nice topic BTW.
That reminds me with a 2006-movie called Idiocracy. Maybe we could make use of the TV series ‘Miami CSI’ to infer that someone who wasn't smart enough to hunt, fight and survive in the new age environment, would get whacked by another human. That someone has to be smart enough so that not to be whacked. Thus, we conclude that 6000 BC or so, the term war was created, and we can also claim that wars have made humans more intelligent, according to the study. But, we still we have Flynn effect.
Oh yeah, I liked Idiocracy, was pretty funny.
Sexual selection doesn't favor intelligence? If anything, it actually favors stupidity. Lower class poor people with low IQ have the most children, have first sexual intercourse earlier, marry and divorce more often.
Krzysztof B: Today they do but maybe not in the past.
If we're no longer selecting for intelligence in the way we used to (arguable), it should be kept in mind that, equally, we are no longer selecting against intelligence in the way we used to. Big heads no longer mean dead moms and babies, to give one example.
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