Sir Peter Brian Medawar, OM CBE FRS (28 February 1915 – 2 October 1987) was a British biologist born in Brazil, whose work on graft rejection and the discovery of acquired immune tolerance was fundamental to the practice of tissue and organ transplants. He was awarded the 1960 Nobel Prize in Physiology or Medicine with Sir Frank Macfarlane Burnet.

Until he was partially disabled by a cerebral infarction, Medawar was Director of the National Institute for Medical Research at Mill Hill.

Medawar was born on 28 February 1915, in Petrópolis, Brazil (a town 40 miles north of Rio de Janeiro) of a British mother (née Edith Muriel Dowling) and a Lebanese father, Nicholas Medawar, who was a Maronite Christian.

Medawar's status as a British citizen was acquired at birth: "My birth was registered at the British Consulate in good time to acquire the status of 'natural-born British subject'.Medawar left Brazil with his family for England "towards the end of the war", and he lived there for the rest of his life.

Medawar was educated at Marlborough College and Magdalen College, Oxford, where he eventually became a Fellow.

Medawar was professor of zoology at the University of Birmingham (1947–51) and University College London (1951–62). In 1962 he was appointed director of the National Institute for Medical Research, and became professor of experimental medicine at the Royal Institution (1977–83), and president of the Royal Postgraduate Medical School (1981–87). Medawar was a scientist of great inventiveness who was interested in many other subjects including opera, philosophy and cricket.

He was knighted in 1965 and appointed to the Order of Merit in 1981.

In 1959 Medawar was invited by the BBC to present the broadcaster's annual Reith Lectures - following in the footsteps of his colleague, John Zachary Young, who was Reith Lecturer in 1950. For his own series of six radio broadcasts, titled The Future of Man, Medawar examined how the human race might continue to evolve.

Whilst attending the annual British Association meeting in 1969, Medawar suffered a stroke when reading the lesson at Exeter Cathedral, a duty which falls on every new President of the British Association. It was, as he said, "monstrous bad luck because Jim Whyte Black had not yet devised beta-blockers, which slow the heart-beat and could have preserved my health and my career". Medawar’s failing health may have had repercussions for medical science and the relations between the scientific community and government. Before the stroke, Medawar was one of Britain's most influential scientists, especially in the medico-biological field.

After the impairment of his speech and movement Medawar, with his wife's help, reorganised his life and continued to write and do research though on a greatly restricted scale. However, more haemorhages followed and in 1987 Medawar died. He is buried — as is his wife Jean (1913–2005) — at Alfriston in East Sussex.

Medawar declared:

... I believe that a reasonable case can be made for saying, not that we believe in God because He exists but rather that He exists because we believe in Him... Considered as an element of the world, God has the same degree and kind of objective reality as do other products of mind... I regret my disbelief in God and religious answers generally, for I believe it would give satisfaction and comfort to many in need of it if it were possible to discover and propound good scientific and philosophic reasons to believe in God... To abdicate from the rule of reason and substitute for it an authentication of belief by the intentness and degree of conviction with which we hold it can be perilous and destructive... I am a rationalist—something of a period piece nowadays, I admit...

Sir Peter was also a realist in pointing out in his book "Advice to a Young Scientist" that there is no quicker way for a scientist to bring discredit on himself and his profession particularly when no declaration is called for, than to declare that science knows or will know the answers to all questions worth asking. Sir Peter added that questions that do not admit a scientific answer should not be assumed to be non-questions. "We must turn to imaginative literature and religion for suitable answers!"

Erwin Schrödinger, famous quantum physicist expressed a similar idea in saying: "Science puts everything in a consistent order but is ghastly silent about everything that really matters to us: beauty, color, taste, pain or delight, origins, God and eternity."

Research

His involvement with what became transplant research began during WWII, when he investigated possible improvements in skin grafts. It became focused in 1949, when Burnet 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.

With Rupert Billingham, he published a seminal paper in 1951. Santa J. Ono, the American immunologist, has described the enduring impact of this paper to modern science.

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.

Medawar's 1951 lecture An unsolved problem of biology (published 1952) addressed aging and senescence, and he begins by defining both terms as follows:

We obviously need a word for mere ageing, and I propose to use 'ageing' itself for just that purpose. 'Ageing' hereafter stands for mere ageing, and has no other innuendo. I shall use the word 'senescence' to mean ageing accompanied by that decline of bodily faculties and sensibilities and energies which ageing colloquially entails.

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 iterrelated 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.

Books

Medawar was recognized as a brilliant author: Richard Dawkins called him "the wittiest of all scientific writers" and New Scientist magazine's obituary called him "perhaps the best science writer of his generation".He was also awarded the 1987 Michael Faraday Prize "for the contribution his books had made in presenting to the public, and to scientists themselves, the intellectual nature and the essential humanity of pursuing science at the highest level and the part it played in our modern culture".

His books include The Uniqueness of Man, which includes essays on immunology, graft rejection and acquired immune tolerance; Induction and Intuition in Scientific Thought; The Art of the Soluble, a book of essays, later reprinted in Pluto's Republic; Advice to a Young Scientist; Aristotle to Zoos (with his wife Jean Shinglewood Taylor); The Life Science, The Limits of Science and his last, in 1986, Memoirs of a Thinking Radish, an autobiography. One of his best-known essays is his 1961 criticism of Pierre Teilhard de Chardin's The Phenomenon of Man, of which he said: "Its author can be excused of dishonesty only on the grounds that before deceiving others he has taken great pains to deceive himself".

• The Future of Man: the BBC Reith Lectures 1959, Methuen, London 1960
• Induction and Intuition in Scientific Thought, Methuen & Co. London 1969
• The Hope of Progress: A Scientist looks at Problems in Philosophy, Literature and Science, Anchor Press / Doubleday, Garden City 1973
• The Threat and the Glory: Reflections on Science and Scientists (ed.: David Pyke), a posthumously collected volume of essays, Harper Collins 1980