The present study adds to the sparse but important literature by assessing the relative importance of growth at prenatal, early infancy, late infancy, and late postnatal periods on the intellectual functioning of 9-year-old Thai children (n = 560)

My first problem with the study is that it doesn't extend into adulthood.

It is stated in this study that the heritability of intelligence increases drastically from infancy to adulthood (from 20% to 80%). Genes become more and more influential as they have more time to express themselves. Therefore the effects of the environment will be exaggerated in this study since only children, who are more susceptible to their environments, were tested.

The heritability of intelligence increases from about 20% in infancy to perhaps 80% in later adulthood.