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Tuesday, August 10, 2010

The g factor and the heritability of IQ

From Wikipedia:

"The general intelligence factor (abbreviated g) is a controversial construct used in the field of psychology to quantify what is common to the scores of all intelligence tests. It was postulated in 1904 by Charles Spearman and subsequently developed into a theory in 1923.

Spearman, who was an early psychometrician, found that schoolchildrens' grades across seemingly unrelated subjects were positively correlated, that these correlations reflected the influence of a dominant factor, which he termed g for "general" intelligence. He developed a model in which all variations in intelligence test scores are explained by two factors. First, a factor specific to an individual mental task: the individual abilities that would make a person more skilled at a specific cognitive task. And second, a general factor g that governs performance on all cognitive tasks."

The idea is that we're all born with a certain innate intelligence, and we can then take that intelligence and apply it in any direction we fancy.

This makes intuitive sense; bright people tend to show their intelligence across a wide range of subjects. When I think of smartest people I know, I find that their accurate recollections tend to go hand in hand with mathematical ability, common sense, verbal adeptness, and superior insight.

It seems an inescapable conclusion: some people are bright, some less so. Very few would argue with this. The only controversy attendant upon the issue of intelligence seems to be about the relative roles played by genes and the environment in its formation.

I first became interested in the nature/nurture controversy back in 1973, partly because it had aroused such violent feelings. After doing a little reading, it quickly became apparent that the geneticists -- the nature camp -- were right, and the nurture camp guided by ideology. (I came to this conclusion at age 19, a time in my life when I was completely apolitical.) If you look at the separated monozygotic (identical) twin studies, and the separated sibling studies, the evidence is overwhelming. The IQs of adopted children are much closer to that of their biological relatives than to the families they had grown up in -- regardless of the economic status of either family they were raised in. And the separated monozygotic twins ended up with commensurately closer IQs than did the separated ordinary siblings.

Certainly there are cases of extreme deprivation which affect IQ strongly. But for the most part, 85% of the variance in IQ is determined by genetic factors, and 15 percent by the early environment. These are the numbers given by people on the hereditarian side of the argument, who were perfectly willing to concede that environment plays a role. People on the other side of the argument, however, were unwilling to assign any role at all to genetics despite the overwhelming evidence. In fact, whenever anyone pointed to such evidence, they would respond by calling him names such as "racist" and "Nazi."

Whether or not genes play a role in determining IQ is a scientific question, not a political or moral one. Yet the hereditarians' opponents kept trying to turn it into a political issue, and ascribed a false morality to inaccurate conclusions.

There was a group at my college who called themselves "Science for the People," headed by Richard Lewontin. They objected to any studies which might lead to politically incorrect conclusions. Their primary target when I was there was E.O. Wilson, who is today widely viewed as the father of sociobiology. (Sociobiology posited that evolution has resulted in different mating strategies between the genders across the animal kingdom.) The group might more accurately have been called, "Abolish Science for the People." They were bookburners, plain and simple, straight out of Ray Bradbury's "Fahrenheit 451."

Liberals today mock Creationists who abjure evolution in favor of Intelligent Design. Yet the loudest voices decrying the study of evolution when I was in college were liberals who hated the conclusions that an open-minded study of the field led to.

Another of the voices raised in opposition to the genetic basis of IQ was Stephen Jay Gould, who wrote The Mismeasure of Man, an attempt to debunk the notion. His basic thesis was that since the phrenologists of the 19th century turned out to be wrong in their theories about head shape determining character, and since one of the hereditarians (Sir Cyril Burt) had fudged his data, the entire field must therefore be wrongheaded. This is like saying that because doctors used to prescribe leeches, and because Josef Mengele was a doctor, all of modern medicine must be a sham.

When I read later that Gould had been raised by his father to be a Marxist and absolutely abhorred the thought of any possible racial differences, it was a real "aha" moment.

Studying the heritability of IQ and then listening to the arguments of Lewontin and Gould were very enlightening early exposures to the liberal mentality.

Coincidentally, I just argued with a liberal today about this. After I quoted a few well-known statistics she angrily cried out, "I find your facts really offensive!"

Yes, she actually said that: she finds facts offensive. It was a tacit admission of... everything.

I thanked her for summarizing the liberal mentality so succinctly.


Anonymous said...

John, While I tend to agree about the role that our genes play in our intelligence, why then is it that unintelligent people sometimes produce brilliant children, and brilliant adults sometimes have average children? And why are some siblings much smarter than others, when presumably they come from the same gene pool?

Yes, liberals will always object to any theory that suggests that we don't all have the same innate opportunity to succeed. Julie

John Craig said...

Julie -- Genes are distributed randomly in any coupling, which is why siblings don't necessarily look like each other. Identical twins have the same set of genes, and the difference in intelligence between them is almost always minimal. Non-monozygotic siblings share, on average, 50% of their genes (they get half of their genes from each parent, but the particular genes are random), so there is a wider variance between them. As far as dull parents producing brilliant children, it happens rarely, but it does happen, and it's just the luck of the draw as far as the child inheriting the right set of genes from each parent. One thing the geneticists do know is that no one gene controls intelligence, there are many involved.

It's actually much more likely that two brilliant parents will produce relatively less intelligent offspring, simply because of regression towards the mean. (This regression happens in all sorts of traits, not just intelligence, by the way.) I remember reading what I thought was a particularly brutal comment once from William Shockley, the Nobel Prize-winning physicist who later gained infamy for daring to publicly say that the differences in IQ between the races was mostly due to genetic reasons. He said, "Regression toward the mean is very real -- my own children are living proof of that."

Anonymous said...

Though incidental to the main point of the post.... Creationists are not the only camp who propose the Intelligent Design theory.

Darwinism is typically believed to be a scientific explanation for evolution of life forms. Most Darwinists believe that physics and probability explain not only the transition of all life forms from the simplest ancient forms to its myriad of present day complexity, but also the origin of life itself.

However, on this last point there is a gaping hole in Darwinist 'physics and probability', i.e. purely scientific, explanation for it all. There is no credible scientific theory to explain how life got going. Even the simplest life form is immensely complex. Any single component of this life form would take an incredible stroke of luck to come together even given mind boggling periods of time to occur. One estimate is that the very simplest life form has over 200 different proteins. How would these 200 proteins form by chance, how would they end up in close enough proximity to produce life, what would have contained them so they could function together, etc. etc.?

I recently watched Ben Stein's 'No Intelligence Allowed'. Its not a great movie, but near the end Stein attempts to pin Darwinist heavyweight Richard Dawkins down on the origin of life. Dawkins replied that life might have been seeded here on earth by aliens. Sounds like an Intelligent Design to me. And it begs the question how did those aliens come to life? Dawkins response only kicks the can down the road.

Though there is a conflict between 'Creationism' and Darwinism, that oversimplifies the problems with Darwinism - and one can disagree with Darwinism as a 'scientific' explanation for all living things without being a Creationist. We simply don't know.

I once listened to a lecture by Stanford scientist Robert Moffat, and expert in experimental methods for the study of heat transfer. Moffat related a story: he was at a fellow professor's house having dinner, and the desert was something baked in an oven that collapsed during baking. Moffat looked at the failed result and offered a scientific theory involving heat transfer, convection etc. to explain the collapse of the desert. His friend explained that Moffat's theory depended on the desert being cooked in its present orientation, but it was actually cooked upside down and then flipped to serve.

The cautionary tale demonstrates the dangers of looking at a set of data and drawing conclusions when there may be more to the story. Experimentally proving a theory takes extreme diligence. Darwinism is incredibly far away from being a proven theory, yet its taken for granted as fact by most in the US.

One doesn't need to be a bible thumping moron to question Darwinsim as the sole explanation for life in all its forms. And most people who take Darwinism as a proven theory have probably never thought about it critically - they just assume that mankind has a scientific explanation for all that exists.

- Ed

Anonymous said...

Following the Second World War, the idea that anyone could have any inborn traits - including IQ - became political dynamite. Any mention of nature as a determining factor, and this would remind everyone of Nazi eugenics and white supremacism. By contrast, the notion of the mind as a blank slate appealed to a nation built on democracy. Ironically, this led to a load of misogynistic theories about 'refrigerator mothers' and 'schizophrenogenic mothers' respectively causing autism and psychotic disorders (these conditions now being known to have natural causes).

I read a very good book about this nature vs. nurture debate by Steven Pinker. He includes a bit which I think is appropriate regarding the liberal you were talking to:
"Feminism is widely seen as being opposed to the sciences of human nature. Many of those scientists believe that the minds of the two sexes differ at birth, and feminists have pointed out that such beliefs have long been used to justify the unequal treatment of women...therefore, it might seem, the theories that are most friendly to women are the Blank Slate - if nothing is innate, differences between the sexes cannot be innate. The belief that feminism requires a blank slate...has become a powerful impetus for spreading disinformation"

Interestingly, *not* all liberals agree with the Blank Slate doctrine. The LGBT community very much supports the idea of there being a natural cause of homosexuality & transsexualism (as it happens, scientists have found brain differences supporting this theory). Some feminists such as Christina Hoff Sommers also reject the Blank Slate, but they're rare. As for IQ, the liberals I've met do tend to argue that intelligent children are only that way because their parents help them more, or because they attend a better school - they seem reluctant to attribute differences in the childrens' abilities to genes.

John Craig said...

Anon --
That's an excellent summation of the liberal and in particular, feminist, attitude towards genes and IQ. Thank you.

Unfortunately for the liberals, all of the evidence on separated siblings and separated monozygotic twins points to the strong role of genes when it comes to differences in IQ.