- Heredity: He wanted to understand how human traits are passed on from parents to children, and how these traits vary within a population.
- Eugenics: He believed that by understanding heredity, it was possible to improve the human race through selective breeding.
- Statistics: He developed a number of statistical techniques, including correlation and regression analysis, which are still used today in various fields.
- Intelligence: He was one of the first researchers to study intelligence and its distribution in the population.
- Twins Studies: He conducted extensive studies on twins to understand the relative contributions of nature and nurture on various human traits.
- Fingerprints: He developed a system for classifying fingerprints, which is still used in forensic science today.