English zoologist and morphologist known for his contributions to experimental embryology, anatomy, and evolution.

Concerned with analyzing developmental processes, de Beer published Introduction to Experimental Embryology (1926), in which he noted that certain structures (such as some cartilage and odontoblasts of dermal bones) previously thought to be derived from mesoderm according to the germ-layer theory were formed instead from ectoderm (neural crest). Of substantial importance is his Development of the Vertebrate Skull (1935). He was also interested, as were many of his generation, in the experimental, chemical, and physiological bases of embryonic development, a subject on which he wrote a text with Julian Huxley called The Elements of Experimental Embryology (1934).

In Embryos and Ancestors (1940) he developed the concept of paedomorphosis, the retention in the adult of juvenile or infantile characteristics of ancestors, in opposition to phylogenetic recapitulation, the theory that an organism during embryonic development repeats the adult stages of its ancestors. He then suggested “clandestine evolution” to account for the absence in the fossil record of preliminary stages, because they occurred in the soft tissues of young ancestors. He discovered the sternum in the fossil Archaeopteryx, the reptilian and avian features of which led him to propose mosaic evolution, whereby piece-by-piece change marks the evolution of one type of animal to the next. He also did fundamental research on the pituitary gland.

His antiquarian interests are shown by his application of biology to such historical problems as tracing the route of Hannibal's march across the Alps (by pollen analysis, glaciology, and other techniques) and tracing the origin of the Etruscans in Asia Minor by blood group data.

De Beer taught at the University of Oxford (1926–38) and at University College, London (1945–50). He was director of the British Museum of Natural History (1950–60). He was knighted in 1954 and received many honours, including the Darwin Medal of the Royal Society (1958) and the Linnean Society Gold Medal (1958). He also published Embryology and Evolution (1930), Vertebrate Zoology: an Introduction to the Comparative Anatomy, Embryology and Evolution of Chordate Animals (1962), Charles Darwin: Evolution by Natural Selection (1963), and Atlas of Evolution (1964).