lolb
Regardless, I agree that g exists in at least a limited sense, but I maintain that there is insufficient evidence to demonstrate that it emerges from innate, immutable physical properties of the brain, and you still can't attribute life success to it.
"Intelligence is what intelligence tests measure." -- Edward Boring
I'm actually surprised by how few comments have been made regarding the actual nature of intelligence in this thread. yummyfajitas' parent comment is one of those few, and he equates intelligence as we understand it with g, the hypothesized general intelligence posited by psychometricians.
y.f. makes the same two arguments that psychometricians make for the validity of g as a representation of human intelligence,[1] which are supposed to demonstrate g's "internal validity" and "external validity". The former refers to the positive correlations between various (supposed) intelligence tests (described in the jargon as the "positive manifold"), and the latter to the positive correlations between g and supposed success in life. Broadly, the internal validity argument proves the "general" in "general intelligence", whereas the external validity argument proves the "intelligence".
The first wrinkle in these arguments is the claim that all human intelligence tests positively correlate with each other to give a universal intelligence factor. This is false; there exist demographics where g is _not_ the predominant factor explaining inter-demographic test score differences.[2]
Here is another problem. Psychometricians tend to decide whether some test metric measures intelligence by how well it correlates with existing "intelligence tests" that're g-associated. y.f. does this in his comment: "It is relatively independent of cultural knowledge: i.e., french is nearly independent of g (1), while physics, plumbing and loading irregularly sized boxes into a truck are highly correlated to g". (I.e., French tests can't be real tests of intelligence, since they don't correlate with g, but physics, plumbing, and bin packing must be, because they do.) But this renders the internal validity argument circular: its two prongs now become: (1) g must exist because intelligence tests correlate positively, and (2) and intelligence tests are those tests that correlate positively with g. The circle closes.
The external validity argument supposedly rescues the g concept from this trap, by demonstrating that g correlates vaguely with real-life behaviours. Unfortunately, the correlations are nowhere near perfect, that g correlates with success doesn't suffice to show causality, and pointing out the correlations does not eliminate the underlying circularity in g's definition. All in all, the evidence is inadequate to reject the null hypothesis that there is no causal link between g and life success.
[1] Well, I say "human intelligence", but if I recall correctly, at least one psychometrician even tried to argue that g might well be a cross-species phenomenon!
[2] Dolan, C.V. Roorda, W., and Wicherts, J. M. (2004). "Two failures of Spearman's hypothesis: The GATB in Holland and the JAT in South Africa", Intelligence, vol. 32, p. 155-173.
I genuflect at your feet, sir.
IQ is a useful (if not especially real) measure, but less so than other measures, it is culture-specific, and it is hardly "highly heritable"; Devlin et al. showed a while back that its narrow-sense heritability is about 35% at best, and most studies of IQ's heritability grossly overestimate it by failing to control for a multitude of environmental effects. And psychometricians don't seem to get how factor analysis renders their beloved general intelligence measure a tautology, so it's understandable why someone would regard their work as BS.
[Edit to add some of the "cold hard facts about IQ" that IQ pushers like the parent comment don't tell you: IQ's heritability varies with socioeconomic status from about 80% to virtually zero, and also increases with age, which makes any claim about IQ having a high heritability across the board extremely suspect.
Note also that despite the name, heritability isn't a measure of 'how genetic' a trait like IQ is; IQ pushers often take advantage of that misunderstanding. Heritability is merely a rough estimate of the ratio of a trait's variance explainable by genetics to the trait's total variance in a population; as such heritability varies between groups, between environments, and between times. It is neither necessary nor sufficient to demonstrate that a trait is 'genetic'.]