Quoting an insightful comment on TFA: [quote] It is simply wrong to state that intelligence is 50% genetic and 50% environmental. This is probably the most common misconception about the meaning of the term "heritability". Heritability does NOT measure what fraction of a trait is genetic. It measures how much genetic variability contributes to the variability of that trait in that population. This sounds like a subtle distinction, but it is MAJOR. First of all, consider a thought experiment. What would happen if we made a herd of dolly's sheep (clones) that are genetically identical. Would they produce exactly equal quantities of milk? Of course not, because we all know that environment will influence milk production. So would we conclude that milk production has no genetic contribution? of course not! To quote my old friend Tim Tully "Of course its genetic. They are making milk for christ sake! (well, thats a rated G version of the quote anyway)" So this little example demonstrates that the quantity we call "heritability" does not measure genetic contribution to a trait in any meaningful or absolute sense. "Heritability" does not mean "inheritable". "Heritability" depends on the particular constellation of genetic variants in THAT POPULATION. And how those particular variants influence the trait. But there is a second and even deeper issue, which is that even when genes DO influence a trait, they do so by interaction with each other AND by interaction WITH THE ENVIRONMENT! so a given gene may or may not influence a trait depending on the environment, and depending the other gene variants that happen to be in that particular animal. And the magnitude of the gene's effect size will also vary depending on environment and the other genes too! This almost certainly contributes to the so called "missing heritability" problem that runs rampant in human genetic studies. Bottom line: its an interesting study and blog post. But the claim to quantify % of genetic influence on intelligence is dead wrong, and actually very dangerous. Josh Dubnau, Assoc. Prof. CSHL, geneticist.[/quote]