He might have been a better writer to have replaced "those Nigerian babies" with "these babies" because after all 5% of the babies of European descent lack the gene(s) too.

Thanks for reminding us of the context of Saletan’s quote. Of course there is a lot more to it than that.

Firstly: It is not 5% of all babies of European descent that are disadvantaged, but 5% of American babies of European descent. I’ll show why this is significant later.

Secondly: As you suggested, the gap is not as wide as “SomeoneElse’s” excerpt makes it appear since the differential is not 10% but 10-5%, that is a 5% disadvantage.

Thirdly: Here’s where the devil is in the detail. There is good reason to suppose that a greater number of less developed people breast-feed their babies.

Suppose for example 90% of Nigerian mothers breast fed their babies, the 10 babies not breast fed and 9 (10%) of the breast fed babies out of the 90 would be disadvantaged, right? (10% of 90% is 9). So 19 % of the Nigerian babies would be disadvantaged.

Now suppose only 75% of American mothers breast fed their babies, right out of the gate that would leave 25% disadvantaged, plus another 5% of that 75%, 3 or 4, namely at least 28% of American babies of European descent would be disadvantaged.

Of course I don’t have the time to find out the percentage of breast-fed American vs the percentage of breast-fed Nigerians. In which case we could tell Saletan that overall Nigerian babies would be LESS disadvantaged in this particular way, unless he can show that American mothers breast feed as much or more than Nigerian mothers. But Saletan’s rather pompous assertion, “Don’t tell me those Nigerian babies aren’t disadvantaged,” is committing the fallacy of begging the question.

Unless he goes into a less superficial analysis of the data presented to him, as with the question of head size he is once again allowing himself to be overwhelmed by his admiration rather than his analysis of the data and its presenters.