In terms of social groups, ersatz racial classifications or cultures, there are no indications that social categorization is a determinant of intelligence or innate cognitive ability. Three factors affect intelligence, physiological makeup and the facilities of the brain; the type of education that is required to make a living and to survive; and artificial education.
When the human brain is compromised by prenatal, genetic and other factors that cause syndromes, defects, disorders,malformations and deficiencies in the brain, then intelligence is compromised congenitally. There is no way that the individual will be able to improve or repair that damage. This type of congenital problem crosses all racial, ethnic, cultural and economic boundaries. As a result, the idea of "nature" as a determinant of intelligence, depending on one's race or other social definition is a logical, economic and political fallacy that exists more for deviant personal, economic and political reasons than as any legitimate scientific endeavor.
When the individual's environment leads to malnutrition, disease, injury to the psyche or body, or accident that results in brain damage, we will find that such factors as mental illness in the parents or caregivers, along with drug and alcohol related emotional and physical abuse cross all economic, social and other artificial boundaries. As a result, attempting to associate this type of brain damage with economic or social class, nationality or race will result in faulty paradigms for which there will be instant proof of exceptions on a sufficient scale to negate the claims.
When oppression is used to deny opportunity to have educations, to foster cultures and activities (such as illegal drug related environments), and to self justify the privileges accruing to selected elites, there will always be someone to come along and demonstrate superior intelligence without being a member of the privileged elite. In many cases, these individuals can end up starting movements that cause the downfall and destruction of the lifestyles of the privileged elites. From Spartacus to Ghandi, to Dr. Martin Luther King, there are plenty of examples to prove beyond a shadow of a doubt that environment has a far more serious impact on the population's intelligence as a whole than their congenital situation.
It is widely rumored that the average American citizen has an IQ in the low 90s. The average American is not a racial, ethnic, or other "minority". A 91 IQ level is alarmingly low, making for inquiry into either the quality of intelligence testing or the average intellect, one or the other.