Kevin Mitchell has a posting at Wiring the Brain (here) on the genetics of intelligence. This is a little off the subject of this blog, consciousness, but it is an interesting inversion of thought which happens often in brain science turning ideas on their heads, so to speak.
He points out that we have known for a long time that intelligence/IQ/g is inherited to a significant degree. And now that we have the human genome available, we should be able to figure out which genes are important to intelligence. But, we have found too many with some small effect on intelligence and too few, well none, with any sizable effect. So we cannot find the gene/s ‘for intelligence’ that we expected.
It seems like we have genes that together give us a healthy, fit, smart individual. No single outstanding genes ‘for healthy’, ‘for fit’ or ‘for smart’. Instead we have to deal with failure of a gene (from a large group) any one of which could leave us sick, unfit and/or stupid. No genes ‘for intelligence’ but rather alleles/mutations ‘for stupidity’.
If this subject interests you, read the original post linked above. If not than simply think of it as an example of how models have to sometimes by inverted or even turned inside out in the light of evidence.