Sir Peter Brian Medawar OM CH CBE FRS (/ˈmɛdəwər/; 28 February 1915 – 2 October 1987)[1] was a British biologist and writer, whose works on graft rejection and the discovery of acquired immune tolerance have been fundamental to the medical practice of tissue and organ transplants.

With his doctoral student Leslie Brent and postdoctoral fellow Rupert E. Billingham, he demonstrated the principle of acquired immunological tolerance (the phenomenon of unresponsiveness of the immune system to certain molecules), which was theoretically predicted by Sir Frank Macfarlane Burnet.

[7] Medawar was born in Petrópolis, a town 40 miles north of Rio de Janeiro, Brazil, where his parents were living.

He was the third child of Lebanese Nicholas Agnatius Medawar, born in the village of Jounieh, north of Beirut, Lebanon, and British mother Edith Muriel (née Dowling).

(Pamela was later married to Sir David Hunt,[10] who served as Private Secretary to prime ministers Clement Attlee and Winston Churchill.

"[8] Medawar left Brazil with his family for England at the end of World War I,[13] in 1918[14][15] and he lived there for the rest of his life.

At 18 years, when he was of age to be drafted in the Brazilian Army,[17] he applied for exemption of military conscription to Joaquim Pedro Salgado Filho, his godfather and the then Minister of Aviation.

[9] He hated the college because "they were critical and querulous at the same time, wondering what kind of person a Lebanese was—something foreign you can be sure",[19] and also because of its preference for sports, in which he was weak.

[9] An experience of bullying and racism made him feel the rest of his life "resentful and disgusted at the manners and mores of [Marlborough's] essentially tribal institution," and likened it to the training schools for the Nazi SS as all "founded upon the twin pillars of sex and sadism."

He also worked at the Sir William Dunn School of Pathology supervised by Howard Florey (later Nobel laureate, and who inspired him to take up immunology) and completed his doctoral thesis in 1941.

[23] 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.

His predecessor Sir Charles Harrington was an able administrator such that taking over his post was, as he described, "[N]o more strenuous than ... sliding over into the driving-seat of a Rolls-Royce".

[23] Medawar's first scientific research was on the effect of malt on the development of connective tissue cells (mesenchyme) in chicken.

[26] Medawar's involvement with what became transplant research began during World War II, when he investigated possible improvements in skin grafts.

[28][29] 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.

Their experimental proof of Burnet's hypothesis was first published in a brief article in Nature in 1953,[32] 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".

[33] 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.

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).

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...

For his own series of six radio broadcasts, titled The Future of Man,[51] Medawar examined how the human race might continue to evolve.

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".

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.

[1] With Frank Macfarlane Burnet he shared the 1960 Nobel Prize in Physiology or Medicine "for discovery of acquired immunological tolerance".

[59] Medawar was 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".

[64] The Department of Science and Technology Studies of the University College London has STS Peter Medawar Prize for undergraduate students.

The evidence that this was indeed the future Sir Peter Medawar—then a schoolboy of 15—was discussed in "Gramophone" in 1995 ("'Gramophone', Die Meistersinger and immunology", by John E. Havard, December 1995).