After completing his PhD, Medawar was appointed a Rolleston Prizeman in 1942, senior
research fellow of
St John's College, Oxford, in 1944, and a university demonstrator in zoology and comparative anatomy, also in 1944. He was re-elected
fellow of Magdalen from 1946 to 1947. In 1947, he became Mason Professor of Zoology at the
University of Birmingham and worked there until 1951. He transferred to
University College London in 1951 as Jodrell Professor of Zoology and Comparative Anatomy. He was head of the transplantation section of the
Medical Research Council's clinical research centre at Harrow from 1971 to 1986. He became professor of experimental medicine at the
Royal Institution (1977–1983), and president of the
Royal Postgraduate Medical School (1981–1987). Medawar's involvement with what became
transplant research began during World War II, when he investigated possible improvements in
skin grafts. His studies particularly concerned solution for skin wounds among soldiers in the war. In 1947, he moved to the University of Birmingham, taking along with him his PhD student Leslie Brent and postdoctoral fellow Rupert Billingham. His research became more focused in 1949, when Australian biologist
Frank Macfarlane Burnet, at the
Walter and Eliza Hall Institute of Medical Research in Melbourne, advanced the hypothesis that during
embryonic life and immediately after birth,
cells gradually acquire the ability to distinguish between their own
tissue substances on the one hand and unwanted cells and foreign material on the other.
Santa J. Ono, the American immunologist, has described the enduring impact of this paper to modern science. Based on this technique of grafting, Medawar's team devised a method to test Burnet's hypothesis. They extracted cells from young mouse embryos and injected them into another mouse of different strains. When the mouse developed into adult and skin grafting from that of the original strain was performed, there was no
tissue rejection. The mouse had tolerated the foreign tissue, which would normally be rejected. Their experimental proof of Burnet's hypothesis was first published in a brief article in
Nature in 1953, followed by a series of papers, and a comprehensive description in
Philosophical Transactions of the Royal Society B in 1956, giving the name "actively acquired tolerance".
Research outcomes Medawar was awarded his
Nobel Prize in 1960 with
Burnet for their work in tissue grafting which is the basis of
organ transplants, and their discovery of acquired immunological tolerance. This work was used in dealing with
skin grafts required after
burns. Medawar's work resulted in a shift of emphasis in the science of
immunology from one that attempts to deal with the fully developed immunity mechanism to one that attempts to alter the immunity mechanism itself, as in the attempt to suppress the body's
rejection of organ transplants. It directly laid the foundation for the first successful organ transplantation in humans, specifically
kidney transplantation, carried out by an American physician
Joseph Murray, who eventually received the 1990
Nobel Prize in Physiology or Medicine.
Theory of senescence Medawar's 1951 lecture "An Unsolved Problem of Biology" (published 1952) addressed ageing and
senescence, and he begins by defining both terms as follows: He then tackles the question of why evolution has permitted organisms to senesce, even though (1) senescence lowers individual fitness, and (2) there is no obvious necessity for senescence. In answering this question, Medawar provides two fundamental and interrelated insights. First, there is an inexorable decline in probability of an organism's existence, and, therefore, in what he terms "
reproductive value." He suggests that it therefore follows that the force of
natural selection weakens progressively with age late in life (because the
fecundity of younger age-groups is overwhelmingly more significant in producing the next generation). What happens to an organism after reproduction is only weakly reflected in natural selection by the effect on its younger relatives. He pointed out that likelihood of death at various times of life, as judged by
life tables, was an indirect measure of
fitness, that is, the capacity of an organism to propagate its genes. Life tables for humans show, for example that the lowest likelihood of death in human females comes at about age 14, which in primitive societies would likely be an age of peak reproduction. This has served as the basis for all three modern theories for the
evolution of senescence.
Theory on endocrine evolution Medawar presented a talk on
viviparity in animals (the phenomenon by which some animals give live birth) at a meeting on evolution at Oxford in July 1952. Later published in 1953, he introduced an aphorism: Endocrine evolution is not an evolution of hormones but an evolution of the uses to which they are put; an evolution not, to put it crudely, of chemical formulae but of reactivities, reaction patterns and tissue competences. The notion that evolution and diversity of endocrine function in animals are due to different uses of each hormone rather than different hormones themselves became an established fact. The paper is also regarded as a pioneer in the field of
reproductive immunology. == Personal life ==