Haeckel’s Embryos

In The Origin of Species Charles Darwin wrote that “the embryos of mammals, birds, fishes, and reptiles [are] closely similar, but become, when fully developed, widely dissimilar.” He inferred that all vertebrates “are the modified descendants of some ancient progenitor,” and that “the embryonic or larval stages show us, more or less completely, the condition of the progenitor of the whole group in its adult state” (Darwin 1859, pp. 338, 345). Darwin’s contemporary Ernst Haeckel called this the “Biogenetic Law,” according to which “ontogeny recapitulates phylogeny.” To illustrate the law, Haeckel (1891) produced drawings of vertebrate embryos which have been widely used in biology textbooks ever since (Figure 1).

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