Jews have had a particularly bad time of it historically, and probably the more stupid ones have failed to survive, while the smart ones did. Africa had major towns and cities, but the people who were captured and sold as slaves were often taken from the forest and undeveloped areas. It is likely that the more enterprising even in those days might have gravitated to the cities or escaped into the forest. Thus those brought to the Americas may have not been the most intelligent. Survival in slavery was not usually a product of intelligence, but of physical strength and obedience to orders. Culturally, of course, Jews, Orientals and other Asians place a strong emphasis on education and diligent study. Also, it was not easy for these populations to flourish in this country decades ago.
Just my opinion, but the “Jews” have a rich tradition in study of the Torah. They memorize entire sections and repeat the writings from those studies. This is a mental exercise that sharpens the mind. It also gives them confidence to debate fine points of law and scripture, and socializes them with adults. Most other “ethnic” groups are more worried about GTA-10, playing ball, or getting high. I think the Jews experience is similar to Asian types of rote memorization and then presenting their thoughts on the knowledge gained to parents or teachers.