Pretty simple math, the MLB was drawing from a much larger sample size of humans than the negro leagues. And that is just whites. IIRC the majors were bringing players from Caribbean at the time.No major variation occurred in the racial composition There of the national population between 1940 and 1950. was a slight decrease from 89.8 percent to 89.5 percent in the proportion of white persons in the total population. The percentage of African Americans in 1950 was 10.0 in contrast to 9.8 in 1940.