English embryologist and pioneer in naval camouflage who greatly advanced knowledge of the evolution of vertebrates and, in 1914, was among the first to advocate camouflage of ships by means of “dazzle”—countershading and strongly contrasting patches.

Kerr's scientific education began when he was a student of medicine, but in 1889 he joined an Argentine expedition to the Pilcomayo River in Paraguay, an experience recounted in A Naturalist in the Gran Chaco (1950). In 1891 he entered Christ's College, Cambridge, and upon graduation, led a second expedition to Paraguay to study the lungfish Lepidosiren (1896–97). He returned to Cambridge where he remained until appointed regius professor of natural history at Glasgow in 1902 and professor of zoology in 1903. He held that post until 1935, when he was elected a member of Parliament for the Scottish universities. He was made a fellow of the Royal Society of London in 1909 and knighted in 1919.

Kerr's approach to zoology was morphological and phylogenetic. Although best known for his studies of the embryology of lungfishes, he also published papers on many other zoological subjects. His most important works are A Textbook of Embryology with the Exception of Mammalia (1914–19), Zoology for Medical Students (1921), and Evolution (1926).