So we are unable to judge, and therefore the null hypothesis must be that humans are genetically similar enough that trait variation is explained by external factors?
I think we can judge, and also that the null hypothesis should be that humans are evolutionary creatures like all other creatures on the planet, with groupings exhibiting different traits based on the genetic makeup.
No, but we cannot make any pure empirical judgements, just ones that we know are inflected by our particular social histories. Of course different humans have different traits, but IQ is not a measure of individual traits, its a mass measurement that correlates far more strongly with social factors such as nutrition and education than genetic heritage, which is what the article is saying
Logical =! Empirical (there are many books on philosophy you could read on this subject, probably all of them.)
Science is the study of things that aren't logical. Concepts don't have anything to do with natural systems, they are patterns of thinking fixed into definite shapes to be applied to the natural world. It is precisely what we don't know, and what we don't yet know that we don't know, that scientific practice helps us discover. If you trusted in "logic" all the time you'd just get endless mathematical formulas that look cool and feel nice, but don't have anything to do with the universe more than a cat has to do with a ball of yarn that it's playing with. It is always when we discover things that break logic, that real scientific progress is made, not when we mindlessly follow what is "logical."
I think we can judge, and also that the null hypothesis should be that humans are evolutionary creatures like all other creatures on the planet, with groupings exhibiting different traits based on the genetic makeup.