Shipmaster Sane
You have been weighed
Malnutrition alone can have a serious effect on lifetime IQ, and IQ is at least partially genetic, so consider that a regularly malnourished population might see a decline in overall IQ generationally.There are some sound points to those arguments, but I haven't seen that sort of thing play out on the racial level.
The two examples I can think of where genetics got fucked up to the point it was noticable at 'group' level would actually be the Hapsburgs and Russian royal families. The inbred so much that they were developing real, noticable health issues in succeeding generations.
Well like I said, it is difficult to know how much of an effect it has because these things always come paired with social factors. However, for a simple example, you have things like the Brain Drain in Africa, where the top percent of IQ population statistically flees to pursue opportunities in greener pastures and never returns, leading (among other factors perhaps) to steadily decreasing IQs in some countries, including one small african country where, if I recall, the average IQ is below the threshold for what is normally considered crippling mental disability. I think it's like 65 or something.
The african slave trade, or the Dem run inner city Ghetto, may have had genetic effects on populations as knock on effects from culture. Or consider Mexico, shipping enourmous numbers of it's middle class (and "middle class" is not arbitrary as far as genetic traits) to america, essentially "distilling" any common genetic factors among it's lower class.
For a few "white centric" examples (though any white supremacist worth their salt would stop and bicker about who's "really" white) the repeated genocides and mass starvations of the Irish people and the subsequent dissolution of their culture and diaspora to america may have had negative effects that cross over into the genetic, that some populations are still riding out the aftershocks of to this day.
For a more clinical example, the use of birth control medication makes women gravitate towards men with lower testosterone. A few generations after birth control becomes common, and we have a crisis of masculinity and statistically depressive testosterone levels.
There is an often miserable continuity between culture and genetics.