According to Galton, Intelligence is a low-level property of our nervous system we inherit from our parents.
Galton also stated that individual differences in intelligence are a result of differences in efficiency of operation of simple neural processes.
Galton established the Anthropometric Laboratory in London, which was dedicated in measuring a range of physical attributes and correlate it to intellectual characteristics.
Charles Spearman estimated the intelligence of 24 children in his village school and devised his own concept of intelligence.
According to Spearman, general intelligence is the unitary, biological and inherited determinant of measurable intellectual differences. He likened it to mental energy, a limited resource available to all intellectual tasks.
Alfred Binet is a French lawyer and self-trained Psychologist who gained interest in studying intelligence by observing his two daughters. He was charged by the Parisian authorities to develop tests to identify children in need of special education
According to Binet, intelligence requires the judgement faculty, which is otherwise called good sense, practical sense, initiative, the faculty of adapting oneself to one’s circumstance’.
In the 1930's, Louis Thurstone proposed that intelligence was composed of seven primary mental abilities, demonstrating how intelligence has different dimensions.
Howard Gardner, an educationalist who believes that the classical view of intelligence reflects a Western bias towards logical reasoning, created the theory of multiple intelligences.
Robert Sternberg proposed a theory of intelligence that is structured similarly to a pyramid, named the Triarchic Theory of Intelligence.