Mostly from twin studies. This number (at least the ballpark figure) is essentially uncontested amongst researchers at this point (see e.g. [1]). However, this is the heritability of the variability of intelligence in adults. In children, that number is close to the one you cited. The rest of what you’ve said is essentially true: heritability is extremely complex and we’re only now getting the first few association studies in to ascertain which genomic loci are associated with changes [2].
Mostly from twin studies. This number (at least the ballpark figure) is essentially uncontested amongst researchers at this point (see e.g. [1]). However, this is the heritability of the variability of intelligence in adults. In children, that number is close to the one you cited. The rest of what you’ve said is essentially true: heritability is extremely complex and we’re only now getting the first few association studies in to ascertain which genomic loci are associated with changes [2].
[1] https://www.ncbi.nlm.nih.gov/pubmed/25985137 [2] https://www.nature.com/articles/s41380-018-0040-6