De Beer, Gavin Rylands (1899–1972)

English zoologist. He made important contributions to the theory of embryology and evolution. He disproved the germ-layer theory and developed the concept of paedomorphism (the retention of juvenile characteristics of ancestors in mature adults).

In Introduction to Experimental Embryology 1926, De Beer observed that certain cartilage and bone cells are derived from the outer ectodermal layer of the embryo. This finally disproved the germ-layer theory, according to which these cells are formed from the mesoderm (see germ layer). Paedomorphism was first described in Embryos and Ancestors 1940, refuting the theory that the embryonic development of an organism repeats the adult stages of the organism's evolutionary ancestors.

De Beer's studies of the fossil Archaeopteryx, the earliest known bird, led him to propose mosaic evolution – whereby evolutionary changes occur piecemeal – to explain the presence of both reptilian and avian features.

De Beer was born in London, studied at Oxford and lectured there. In 1945 he became professor of embryology at University College, London, then was director of the British Museum (Natural History) 1950–60. Knighted 1954