Historical reasons: During the slave trade, the British used cargo holds to transport slaves to the United States in batches. During the journey of several days, they only gave a little food and drinking water. As a result, when the ship arrived in the American continent, most of the slaves died, and the only ones who survived were black people with excellent physical quality. The DNA of these black people has been passed on to African blacks now. They are stronger and have better physical fitness than African blacks.

Environmental factors: the United States is more developed and stable than Africa, and its social foundation is far better than Africa. Moreover, there are no food shortages and hunger supply problems in the United States. In such a good environment, Chinese are better than Africans with poor social environment.