Watson was vastly simplifying genomics, as is this letter. To grasp the details requires knowledge of class, culture, nutrition, and genomics.

https://www.nature.com/articles/mp2014105

My criticism of the Nature paper does imply endorsement of Watson, who was equally stuck in 1950's extropolationist macroevolutionary thinking:

1. Take a trait (IQ) that is highly heritable within well-nourished, educated, industrial populations. 2. Observe large average differences between populations that differ dramatically in nutrition, disease burden, schooling, and historical trauma. 3. Assume, without any direct genetic evidence, that the between-group gap must be largely genetic because the within-group heritability is high

I have made an effort to acquaint myself with the ACTUAL literature on evolutionary theory. It is nothing like what popular media would have you believe.