Taller people have higher intelligence than shorter people on average because, brain size is positively correlated with height, and brain size is positively correlated with IQ.

>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...