> General and specific cognitive abilities were studied in intact Swedish same-sex twin pairs 80 or more years old for whom neither twin had major cognitive, sensory, or motor impairment. Resemblance for 110 identical twin pairs significantly exceeded resemblance for 130 fraternal same-sex twin pairs for all abilities. Maximum-likelihood model-fitting estimates of heritability were 62 percent for general cognitive ability, 55 percent for verbal ability, 32 percent for spatial ability, 62 percent for speed of processing, and 52 percent for …
https://www.researchgate.net/profile/Robert_Plomin/publicati...
This is great for Swedish people. The problem is that humanity consists largely of not-Swedish people. Same for most studies of this kind, which are largely concerned with populations that are already genetically closely related; it stands to reason that the differences between people who are closely related will be more attributable to their inborn differences, than the differences between people who are not closely related. They haven't been able to do an interracial, intercultural comparison on this because socioeconomic circumstances are so substantially different between groups (and have been so since the rise of modern empirical research) that it's impossible to set up a decent comparative study.
The g factor is highly heritable, and countless academic works and studies establish it as such, well beyond any reasonable doubt.