mainly to be near the conductor Arturo Toscanini. He was also deeply interested in the life and example of Gandhi, producing an unpublished book-length manuscript on his life. During Jensen's period in San Diego he spent time working as a social worker with the San Diego Department of Public Welfare. IQ and academic achievement Jensen's interest in learning differences directed him to the extensive testing of school children. The results led him to distinguish between two separate types of learning ability. Level I, or associative learning, may be defined as retention of input and rote memorization of simple facts and skills. Level II, or conceptual learning, is roughly equivalent to the ability to manipulate and transform inputs, that is, the ability to solve problems. Later, Jensen was an important advocate in the mainstream acceptance of the general factor of intelligence, a concept which was essentially synonymous with his Level II conceptual learning. The general factor, or g, is an abstraction that stems from the observation that scores on all forms of cognitive tests correlate positively with one another. 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 non-whites. Jensen's most controversial work, published in February 1969 in the Harvard Educational Review, was titled "How Much Can We Boost IQ and Scholastic Achievement?" It concluded, among other things, that Head Start programs designed to boost African-American IQ scores had failed, and that this was likely never to be remedied, largely because, in Jensen's estimation, 80% of the variance in IQ in the population studied was the result of genetic factors and the remainder was due to environmental influences. The work became one of the most cited papers in the history of psychological testing and intelligence research, although a large number of citations consisted of rebuttals of Jensen's work, or references to it as an example of a controversial paper. After the paper was released, large protests were held, demanding that Jensen be fired. Jensen's car tires were slashed, the university police provided him with plain-clothes bodyguards, and he and his family received threats that were considered so realistic by the police that they