Arthur Jensen was born in San Diego, California, and attended the University of California at Berkeley, San Diego State College, and Columbia University. He completed a clinical internship at the University of Maryland's Psychiatric Institute in 1956, after which he won a two-year postdoctoral research fellowship with the Institute of Psychiatry at the University of London, where he worked with Hans J. Eysenck, a prominent psychologist known for his evolutionary approach to human behavior. Eysenck's work in personality theory, measurement, and intelligence—areas that were to become Jensen's specialty—challenged humanistic, psychodynamic approaches that stressed the importance of social factors in human behavior. In 1958, Jensen joined the faculty at the University of California at Berkeley, serving as a professor of educational psychology, and also served as a research psychologist at the Institute of Human Learning. After early work in the area of verbal learning, Jensen turned to the study of individual differences in human learning and intelligence.
Jensen claimed, on the basis of his research, that general cognitive ability is essentially an inherited trait, determined predominantly by genetic factors rather than by environmental conditions. He also contended that while associative learning, or memorizing ability, is equally distributed among the races, conceptual learning, or synthesizing ability, occurs with significantly greater frequency in whites than in blacks. He suggested that from the data, one might conclude that on average, white Americans are more intelligent than African-Americans. Jensen suggested that the difference in average performance between whites and blacks on intelligence tests might be the result of innate differences rather than contrasts in parental upbringing, formal schooling, or other environmental factors. Jensen further surmised from the data that federal educational programs such as Head Start could only raise the IQs of disadvantage children by only a few points and are therefore not worthy of funding. The relative influence of heredity and environment on intelligence tests had been an area of debate since their inception in the 1920s, and the prevailing view of Jensen's contemporaries was that environmental factors in the home and school play the decisive role.
In 1969, Jensen published his views in a long article entitled "How Much Can We Boost IQ and Scholastic Achievement?" in the Harvard Education Review, which rekindled the age-old debate of the relative importance of genetics in determining intellectual ability. Jensen's work was often misquoted by the media and was popularly denounced on college campuses. The belief in a genetic basis for individual and racial differences in intelligence and scholastic performance came to be known as "jensenism." Although Jensen's work in human intelligence has received a mixed reception from professionals in the field, his prolific publications have engaged the serious attention of many researchers and educators in the years since. Jensen's books include Genetics and Education (1973), Educability and Group Differences (1973), Bias in Mental Testing (1979), and Straight Talk about Mental Tests (1980).

Definition of Intelligence

“A working definition of intelligence, then, is that it is the g factor of an indefinitely large and varied battery of mental tests….We are forced to infer that g is of considerable importance in ‘real life’ by the fact that g constitutes the largest component of total variance in all standard tests of intelligence or IQ, and the very same g is by far the largest component of variance in scholastic achievement (Jensen, 1979, pp. 249-50).”

Jensen’s interest in this topic began when one of his graduate students noted that the white special education students he was working with appeared to be more genuinely “retarded” than the students from minority groups who had been placed in special education. In fact, it seemed to Jensen’s student that whereas the white children functioned at a low level both inside and outside the classroom, the minority children sometimes appeared “quite indistinguishable in every way from children of normal intelligence, except in their scholastic performance and in their performance on a variety of standard IQ tests (Jensen, 1974, p. 222).”  Jensen’s student wanted to know if there were any “culture-free” intelligence tests that might explain the differences he observed in his students. This question spurred several experiments, and the results persuaded Jensen that standard g-loaded intelligence tests are fairly good measures of intellectual ability, and that racial differences in average IQ scores are not due to any “culture unfairness” intrinsic to the tests.  Jensen articulated evidence to support these views in his 1969 article.

Jensen accepts Spearman’s idea of a general factor in human intelligence, and his own theory divides intelligence into two distinct sets of abilities:  Level I abilities account for memory functions and simple associative learning, and Level II abilities comprise abstract reasoning and conceptual thought. Jensen concluded from his research that Level I abilities are equally-distributed among the races, whereas white and Asian students demonstrate advantages in tests of Level II abilities. Since Level II abilities appear to be more important for success in school, white and Asian children are at an advantage (Fancher, 1985).

In years since the publication of the 1969 Harvard Educational Review article, Jensen has published a large body of empirical research demonstrating that genetic factors are a substantial source of the variance in individual differences in IQ (Fancher, 1985).  Despite the controversial nature of his claims, in 2003 Jensen won the prestigious Kistler Prize for original contributions to the understanding of the connection between the human genome and human society.