Look at the actual research that supposedly leads to the rejection of that idea. There doesn't seem to be any, except for a bunch of unsupported speculation. A notorious example is the Minessota Transracial Adoption Study or something along those lines. They actually found what was clearly an inherent difference according to their experiment's design, then after they got this uncomfortable result, they found another variable they'd forgotten to control for and attributed it to that, without any further evidence. The science in this field is full of fraud because it's dominated by leftists who will be punished by their peers for publishing politically incorrect findings.