Mendel had many advantages over Galton in his studies of inheritance. Mendel’s peas were true breeding, produced a new generation each year, and yielded large numbers of progeny. The environment had a negligible effect on the traits, and the genetic effect on each trait was due to alleles of a single gene. Mendel’s crosses yielded simple ratios such as 3:1 or 1:1, which could be interpreted in terms of segregation of dominant and recessive alleles.

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By contrast, Galton studied variation in such traits as height in humans. Humans are obviously not true breeding and have few offspring. Galton had one big advantage, though: Whereas most simple Mendelian traits are relatively uncommon, Galton’s traits are readily observed in everyday life. What did Galton discover?