:::I'd like to see some evidence that "Mainstream science is leaning toward high heritability of IQ". For one thing the statement makes no sense, hertability is a measure of a population and not a measure of a trait, one cannot talk about the heritability of IQ, one can only talk about the heritability of IQ within the population that is being investigated.  I don't think "mainstream science" does a great deal of research into IQ and heritability at all, from what is published about heritability there is a discussion regarding how much variation is attributable to gene x environment interactions. Environmental vs gene effects on complex traits are totally unknown (genetic/environmental causation is not measurable, heritability does not measure the genetic effect on "intelligence" ), and their effects on the variation of a trait within a population are far more complex than the simplistic gene-environment dichotomy that is often postulated.  Heritability studies do not measure the effect of  genes on a trait (such as intelligence) in an individual, but the effect of the contribution of genes to the variation of a trait within a population, this is not extrapolable to different populations. A high heritability for "intelligence" (80%) for a sample derived from the "white" US population tells us nothing about the heritability of intelligence in a different population (for example the African-American population), indeed it very much depends on the composition of this sample, if this sample is environmentally homogeneous (and not necessarily representative of the population as a whole), then we would expect genes to contribute greatly to the variation. Heritability is a proportion, the less environment affects the variation, the more genes do and vice versa, or to put it another way, a heritability of 80% for a sample of "white" Americans may only be telling us that this sample is environmentally homogeneous (if they are all middle class, went to well funded good schools etc). From my perusal of the data, most research into heritability is involved with trying to partition environmental effects, genetic effects and environment/gene interactions. The problem with interaction between genes and environment, (gene environment correlation are often partitioned with genetic effects on variation), is the biggest bone of contention in heritability estimates. A great deal of this research is done with laboratory organisms because identifying environmental effects can only be done when a large range of different environments are considered and of course we can use strains that are genetically homogeneous. Twin studies are the most controversial of all studies, because they assume that the similarities between identical twins are all genetic, and assume that identical twins live in identical environments to their non-twin siblings, or can be compared to non-identical twins, i.e. that the differences in IQ correlations between non-identical twins and identical twins must be genetic. This assumption has been challenged. Identical twins may share a great deal of their environment that is not shared by their non-twin siblings. It is likely that as sequencing of whole genomes becomes easier and cheaper, twin studies will be abandoned in favour of comparing inter-individual genetic differences based directly on estimates of gene sharing, in this way a more randomised sampling of different environments will be possible.