Theory that relates the development of an individual to its biological past. The phrase “ontogeny recapitulates phylogeny” was, during the 19th century, one of the main arguments of scientific racism in the Western world. It was first stated by German zoologist Ernst Haeckel in Uber Arbeitstheilung in Natur und Menschenleben (1869) as a way of understanding Evolution. Because the fossil record was very incomplete, Haeckel proposed that it might be possible to read the evolutionary history of species its “phylogeny” through the development of an individual, or “ontology.” He believed that every individual passes through stages that represent the adult development of its ancestors or, as Stephen Jay Gould puts it in The Mismeasure of Man, “an individual, in short, climbs its own family tree.”
Individuals of a species do seem to develop characteristics associated with other animals. Human embryos, for instance, develop (and lose) gill slits on their necks, a three-chambered heart (which expands to four chambers), and a tail. These characteristics seemed to prove the 19th-century idea that evolution was a ladder of progress with humans at the top of the ladder. Recapitulation theory even placed human races in a biologically determined hierarchy. Some races were ranked superior to others; white Western Europeans and Americans were placed on top. Scientists theorized that other human races could be understood by studying the behavior of white children. When 20th-century biologists replaced the model of evolution as a ladder with one of a many-branched bush, they no longer had a place for recapitulation theory, and it was discredited.