THIRTY YEARS OF RESEARCH ON RACE DIFFERENCES IN COGNITIVE ABILITY by Rushton and Jensen

Throughout the history of psychology, no question has been so persistent or
so resistant to resolution as that of the relative roles of nature and nurture in
causing individual and group differences in cognitive ability. The scientific debate goes back to the mid-19th century. Starting with the
widespread use of standardized mental tests in World War I, average ethnic and racial group differences were found. Especially vexing has been the cause(s) of the 15-point Black–White IQ difference in the United States.