How do you explain the IQ difference between, say, American whites and blacks? They should have similar parasite load and nutritional status.
This is strong assumption. Malnutrition (wider concept than just calories) exists in US and there are large differences between ethnic groups.
Interestingly enough, from the same researchers:
Parasite prevalence and the distribution of intelligence among the states of the USA, https://www.researchgate.net/publication/229409035_Parasite_...
>In this study, we tested the parasite-stress hypothesis for the distribution of intelligence among the USA states: the hypothesis proposes that intelligence emerges from a developmental trade-off between maximizing brain vs. immune function. From this we predicted that among the USA states where infectious disease stress was high, average intelligence would be low and where infectious disease stress was low, average intelligence would be high. As predicted, we found that the correlation between average state IQ and infectious disease stress was − 0.67 (p < 0.0001) across the 50 states. Furthermore, when controlling the effects of wealth and educational variation among states, infectious disease stress was the best predictor of average state IQ.Highlights► We compared rates of infectious disease with average IQ across USA states. ► We controlled for education and wealth. ► Infectious disease was the best predictor of average IQ.
Correlation is not Causation: You might want to look at the prevalence of infectious diseases by race according to the CDC.
https://www.cdc.gov/nchhstp/healthdisparities/africanamerica...
Edit: Insert Numbers;
Black People make up 14% of US population and
45% of the total of HIV/Aids
62% of women with HIV/Aids
55% of Gonorrhea
Chalmydia: Black Women 5.2x more likely and Black men 7.3 times more likely as white people
38% of Syphilis cases Black Men and Women over 5 times as likely as white people
37% of TB cases Black people, and 87% of all reported TB cases occurred in racial and ethnic minorities
If the states with lower IQs have a higher percentage of African Americans than the other states, they will have a higher rate of infectious diseases due to the propensity of infectious diseases among that group with respect to others.
PS: The two states with the lowest rate of infectious diseases, Nevada and West Virginia are respectivelly the 2nd and 7th lowest IQ states. #1 lowest IQ, Hawaii was deemed an outlier because of latitude and excluded from the results of the study you linked to.
http://www.americashealthrankings.org/explore/2016-annual-re...
https://www1.udel.edu/educ/gottfredson/30years/Rushton-Jense...
Its worth reading and answers your question, while refuting the OP above
I suggested looking and comparing the magnitudes between different factors and putting them into order of importance.
We know that taller people have higher intelligence than shorter people on average [1]. Compare effect sizes between black and whites and tall and short white males. Now ask if the difference between ethnic groups is important or not.
[1] : https://en.wikipedia.org/wiki/Height_and_intelligence
ps. 90% of genetic variance in human races exists in the African continent. If we clean out all environmental factors, the "smart genes" are probably in Africa. We just need to find them and distribute them.
>Studies on over 700 participants show that individuals with larger brain volumes have higher IQ scores. About two dozen studies using magnetic resonance imaging (MRI) to measure the volume of the human brain have found an overall correlation with IQ of greater than .40
>Within each race, cranial capacity correlated with IQ scores. By age 7, the Asian American children averaged an IQ of 110; the White children, 102; and the Black children 90. Because the Asian American children were the shortest in stature and the lightest in weight while the Black children were the tallest in stature and the heaviest in weight, these average race differences in brain-size/IQ relations were not due to body size.
>Overall, MRI studies show that brain size is related to IQ differences within race. Moreover, the three-way pattern of group differences in average brain size is detectable at birth. https://www1.udel.edu/educ/gottfredson/30years/Rushton-Jense...
Counting neutral variation (the vast majority of genetic variation). You can get plenty of variation in non-coding DNA from drift without any effect on the variance in a trait. In fact, you rarely actually get effects on highly polygenic traits from drift without selection (imagine random directions chosen independently for each of the relevant alleles, and think in terms of the law of large numbers).
If you're getting this from Oded Galor or Deidre McCloskey, they're generally smart people but don't understand population genetics well.