IQ tests measure general intelligence that is 60 percent heritable within whites. Blacks average 15 IQ points below whites. Herrnstein and Murray agnostic on genes versus environment mix but assert partial black genetic inferiority. Heritability within whites excludes all-environmental explanation only if assuming no massive black environmental deficit. High within-group heritability implies zero about between-group genetic differences. Lewontin corn example shows 100 percent heritability within nutrient groups but full environmental cause of group gap. Flynn Effect raises IQ 3 points per decade worldwide matching black-white gap. Dutch IQ rose 21 points in 30 years entirely environmentally. Blacks environmentally disadvantaged as caste-like minority per Ogbu. High SES blacks still lag whites due to caste legacy unlike voluntary immigrant groups. Environmental gap could place average black environment at white 6th percentile implausibly but matched by Dutch generational shifts. IQ not genetically determined due to huge normal environmental sensitivity. Heritability confounds direct and indirect genetic effects via environment. Black twins non-randomize environments due to race-based treatment. Heritability rises with age as environments uniformize. No heritability studies done in mixed black-white populations.