He married in 1957 and had four children.

Born in Leeds, UK, 7 November 1934, Died in London, UK, 8 November 1996

Selwyn's parents owned and ran a small but successful butchers shop in Leeds and originally expected him to follow them in their trade or at least something similar. It was all the more remarkable that he chose instead to devote his life to science and academia given that (so far as is known) no member of his family before him had ever considered continuing their education beyond the then normal school leaving age of 14, let alone gone to university.

As a working class boy growing up in England in the 1930s, and during WWII, it was therefore a great achievement for him to win a scholarship to be educated at the prestigious and ancient Leeds Grammar School. He then went on to study at the University of Edinburgh from which he graduated with a BSc, MB ChB, and MD.

Worked briefly (from 1959–1960) as a house physician in Edinburgh City Hospital before becoming a lecturer in bacteriology at University of Edinburgh Medical School (1961–1966). In 1967 he became one of the youngest-ever Visiting Professors for the World Health Organisation (WHO) at Baroda University in India, as well as a WHO SE Asia medical consultant. He toured India extensively visiting not only towns and cities but also many remote rural areas as part of his WHO project to greatly improve the standards of health and hygiene at various hospitals. He returned from India to become first Reader, then Consultant and finally Professor of Medical Microbiology at Westminster Medical School, University of London.

Whilst continuing as Professor at Westminster Medical School he also simultaneously became Professor of Medical Microbiology at Charing Cross Hospital Medical School, thus running two separate departments (each with its own research and teaching teams) in two different teaching hospitals.

During the 1970s and 1980s he played a significant role as a pioneer in the field of bone marrow transplantation. In particular he was closely involved with the treatment of two ground-breaking cases; those of Simon Bostick and Anthony Nolan. Anthony Nolan's mother went on to found the charitable Anthony Nolan Trust.

Research in the fields of bacteriology and medical microbiology were by no means his only professional interests. Despite his extremely demanding research activities (which often resulted in invitations to present his findings at conferences and guest lectures throughout the world) he also developed world-class expertise in the history and development of medicine, from the dawn of civilization to the then present day and also became a distinguished and popular lecturer in that subject.

He was honorary archivist of the Royal College of Pathology of which he was also a Fellow (FRCPath), President of the Faculty of History and Philosophy of Medicine and Pharmacy, President of the Medical Sciences Historical Society and a Liveryman of the Worshipful Society of Apothecaries where he was also Director of the DHMSA (the Diploma of the History of Medicine at the Society of Apothecaries), an important and popular course and diploma, to which some students even flew in from across Europe (and one from Canada) each week to attend! He led this course to new heights of popularity over the seventeen years of his tenure, until ill health forced his retirement in 1990.

He was an active member of many prestigious research and educationally based clubs and organisations, for example being President of the Osler Club of London and President of the Harveian Society of London (1991–92).