A pioneer of psychometrics and the application of statistical methods to the study of human diversity and the study of inheritance of human traits, he believed that intelligence was largely a product of heredity (by which he did not mean genes, although he did develop several pre-Mendelian theories of particulate inheritance).
Som en pioner indenfor psykometrik og brugen af statistiske metoder til undersøgelse af menneskelig forskellighed og studiet af arvelighed af menneskelige træk troede han, at intelligens langt hen ad vejen var et produkt af arvelighed (med dette mente han ikke gener, selvom han udviklede flere teorier om arvelighed før Mendel).