What did Francis Galton propose in Hereditary Genius?

In his 1869 work Hereditary Genius, Francis Galton proposed that "genius"—defined as inborn, exceptionally high intellectual ability—is a trait that tends to run in families.12

His central argument was that both mental and physical characteristics are equally inherited. Galton further theorized that genius is an extreme manifestation of three combined traits—intellect, zeal, and the power of working—which are shared by all individuals in varying degrees. By asserting that these mental traits are biologically transmitted, Galton sought to provide a scientific basis for his advocacy of eugenics, which he defined as the effort to improve the human species through selective mating to increase the proportion of individuals with superior genetic endowments.12

It is important to note that Galton’s work was limited by the lack of an adequate theory of inheritance at the time, and his focus on biological factors has been widely criticized for failing to account for the significant impact of social, educational, and environmental opportunities on human achievement.12