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05/28/2001 Archived Entry: "IQ"

Another instalment in the 'Conversations with my Evolution and Behaviour supervisor' series:

You should all be aware that the way we measure intelligence in humans is via IQ (Intelligence Quotient) tests. When you conduct an IQ test, you don't just test for one specific thing, you test for a whole range of abilities, such as digit span, verbal reasoning and perceptual fluency, among many others. The theory goes that if you add up the results of all these various tests and take the average, you have your IQ.

If only that were the case. When I heard this, I immediately interjected and said that that couldn't possibly be right since surely these tests all test for different and not necessarily related abilities, e.g. how related is spatial reasoning and memory?

However, there is a relatively popular school of thought that says that there is one underlying basis of intelligence that all of these abilities rely upon, and it's been named the 'g factor'. Now, ignoring whether this hypothetical 'g factor' exists or not, we have to consider what the political implications of a 'g factor' would be.

Keeping in mind that the 'g factor' would essentially be the basis of intelligence, if it existed it would be so much easier for people to say that 'Well, x racial group scores lower on g factor tests than y racial group, so they must be less intelligent,' and thus possibly open the door for all sorts of nasty bias and prejudice.

If it doesn't exist, it would be much harder for people to say that because instead they'd have to claim, 'X racial group scores lower on twenty different intelligence tests than y racial group...' In other words, just having one basis of intelligence makes it easier to put people into boxes than if you have dozens of factors that contribute to intelligence.

As it happens, there isn't a single g factor that determines our intelligence. By doing a bit of nifty factor analysis on the pooled results of huge numbers of IQ tests for many different individuals and seeing how the various tests correlate with each other, it's been discovered that there are a few factors that underpin intelligence. Not dozens, but not just one. These factors 'overlap' in the areas they cover. So for example, digit span (how many numbers you can remember in one go) doesn't rely on just one of these intelligence factors but it draws on several different factors in different amounts.

Among the different underlying factors that determine intelligence is a particularly strong factor named 'gf'. The best intelligence test for deriving a 'pure' value for someone's 'gf' is an analogical reasoning test. Analogical reasoning is when you think about the relationship between two things and apply that relationship to another two unconnected things (it's a simplification, but there you go). So an example would be saying that 'a bird is to air as is a fish to the water'.

And when you think about it, analogical reasoning is a very powerful tool for intelligence in spotting similarities between different situations and applying what you know and have learnt it previous experiences to new experiences. Two excellent cases would be the way that Newton compared the falling of an apple from a tree with the way planets moved, and how Einstein conducted all his thought experiments - gedanken - like 'What happens if I'm in an elevator that's falling?' or 'What would I see if I was travelling at the speed of light?'

The question is, does intelligence have a genetic factor? Yes. Studies have shown that the heredity rate of intelligence is 50%. That means that the variation in intelligence among a population can be attributed half to genetics and half to the environment. Does this genetic factor matter, and do the genes for intelligence automatically determine how intelligent you will be when you grow up?

Well, you'll just have to wait until tomorrow to find out...