B-W IQ gap resists X-factor explanations since both groups share environments. High within-group IQ heritability rules out single VE factors causing 1 SD gap. Flynn concedes many-causes hypothesis implausible per Jensen's logic. COVGE model fails because g is genetically causal with brain endophenotypes. Environments do not correlate with brain endophenotypes contradicting active rGE. Studies confirm causal genetic g ruling out purely environmental construction. Flynn effect likely artifact, non-g gains, heterosis, or time-specific X-factors not applicable to B-W. Ang et al. show Flynn effect uniform across races, sexes, SES like X-factor. Rowe et al. find identical developmental processes and correlations for achievement across Blacks, Whites, Hispanics, Asians. Sibling and half-sibling studies show same variance structures in B-W achievement. Ree and Carretta confirm same g loadings across ethnoracial groups on AFOQT. Jensen's default: genetic differences parsimonious without ad hoc X-factors. Flynn's basketball analogy admits average genetic differences between populations. Non-additive GE insignificant for IQ heritability. B-W gap stable post-infancy matching genetic stability. X-factors empirically ruled out by measurement invariance studies.