Intelligence Did Not Matter Much
by tdaxp ~ June 24th, 2008
A recent post by Gene Expression has mind-opening implications, if you read closely:
Gene Expression: Selection, drift, disease and complexity, all rolled into one….
I would have to say that the distributions here are not totally surprising based on other things we know, this is an empirical confirmation to a great extent of rules-of-thumb which many hold because of the theoretical and experimental insights of a century. For example, it is well known that complex-traits which exhibit a continuous distribution and are highly heritable tend to have weak fitness implications. Conversely, Mendelian diseases are usually classified as diseases for a reason! Additionally, the authors find that diseases which are expressed dominantly, that is, one copy results in the disease, have lower values of Dn/Ds, than those which express recessively so that two copies are necessary. This is what we would expect from the fact that when low frequency alleles which only express as homozygotes are segregating within the population randomly most copies are carried within heterozygotes who are not subject to selection; in other words, there is little purification of these genes unless their frequencies are very high as per Hardy-Weinberg. To make the difference between complex-disease loci and Mendelian ones more concrete, think of it in a non-disease context. Height is a quantitative trait, while eye color seems quasi-Mendelian. HMGA2 is a height locus which explains 0.3% of the variation within a population for the trait in question, while the region around OCA2 seems to account for 75% of the variation in blue-brown eye color. In addition the region around OCA2 may have been subject to selection and this selection may explain the difference in eye color across populations. It seems unlikely that we’ll find strong signatures around height loci that explain the variation of height across populations.
General intelligence is a complex trait that has a continuous distribution and is highly heritable. So, for that matter, do political orientation and personality. Thus, it is likely that general intelligence, personality, and political orientation did not do much for your ancestors.
Your ancestors were winners, because unlike the vast majority of humans who ever lived, they spawned offpsring who are still alive today. But the secret of their succeess was probably something other than how quick they were.
June 24th, 2008 at 2:16 pm
you’re right that there’s a lot more unsaid there. i would add though that the main issue is that heritability & continuity entail that there wasn’t a strong bout of directional or purifying selection because there’s still extant variation. OTOH, you could imagine a scenario where frequency dependent forces keep a balance of polymorphisms within the population. so various intelligent or personality morphs weren’t exactly fitness irrelevant, but, they when at equilibrium there wasn’t a difference from mean population fitness.
June 28th, 2008 at 4:39 am
razib,
It’s an honor for you to comment here.
Thanks for the further information!