This chapter attempts to broadly outline the current understanding of the etiology of intelligence and intelligence-related processes. First, it describes the major concepts that have primarily guided studies of the etiological bases of intellectual abilities and disabilities. Then, the chapter discusses the state of the field's understanding of cases of intellectual abilities and disabilities. A point of view on the Chinese initiative as presented in the CNN electronic publication is described. The chapter describes the major concepts that have been and are used to explore the connection between the genes and intelligence. The evidence pertaining to observations that the genome is a major source of the variations in individuals' intellectual abilities and disabilities is discussed. Studies of various indicators of information processing speed have been prominent in the field of intelligence due to the observation that these indicators reliably correlate with various aspects of intelligence, especially, with the g factor.

The relationship between culture and intelligence is complex and characterized by a lack of consensus regarding the definition and operationalization of each construct. Due to limited or non-existent health care, particular racial and ethnic groups are at greater risk for sensory loss and other health problems that may lower their performance on intelligence measures, for example, higher blood lead levels leading to cognitive deficits. This chapter discusses the measures of intelligence that include g factor, test bias, cultural loading, and test fairness. A number of alternative assessment practices have emerged in recent years in part to address criticisms of the usage of intelligence tests with members of racial and ethnic minority groups. It should be noted that the IQ difference between Black and White 12- year-olds has dropped 5.5 points. Asians and Asian Americans have often obtained the highest group averages on standardized intelligence tests.