Ursula Mittwoch, front centre in black, at the age of 26 in 1950, beneath the Portico of UCL
Ursula Mittwoch was an unusual geneticist who forged her reputation working with Professor Lionel Penrose on chromosomal disorders in the early days of cytogenetics, yet who declared later that she “didn’t much like chromosomes”. She became Professor of Genetics at UCL. She blazed her own luminous path through the second half of the 20th century.
Despite more than 200 publications, including 14 Nature papers through the 1960s alone, many as a single author, her work perhaps did not receive the recognition it deserved, at least among geneticists; but her bold insights into the sexes were appreciated by the media and she wrote regularly (often with a waspish sense of humour) for magazines like New Scientist. In fact, her thinking was decades ahead of its time, more in tune with the renewed interest in epigenetics of recent years. Today, when so many people rebel against a binary definition of sexes, Ursula’s work shows that sex determination is far from a simple switch governed by Mendelian genes but reflects a ‘threshold dichotomy’ – in effect, a quantitative rather than a qualitative difference. To be sure, our genes stack the quantitative odds towards one sex or another, yet the spectrum in between leaves plenty of scope for intersexuality.
Ursula being presented with the painting Mitochondria in Action by Odra Noel, to celebrate her 90th birthday. With (from left) Profs John Allen, Sue Povey, Dallas Swallow and the author, in the Housman Room at UCL in 2014
Ursula was an exemplary scientist. Like the best scientists, Ursula’s ideas reached beyond science, linking myths and history with deep human preoccupations. Commenting on the timing of ‘ensoulment’ – the gradual ‘becoming’ of a human person – Ursula called attention to the ‘exotic error’ of Aristotle and Thomas Aquinas: the notion that ensoulment occurs gradually during embryogenesis, and is complete at 40 days in male embryos, compared with 90 days in female embryos (Mittwoch, 1995). ‘The apparent bizarreness of this idea’, she said, ‘owes less to embryology than to the extreme reluctance of most present-day molecular biologists to take on board quantitative, as opposed to histological and biochemical aspects of development, and to consider the importance of time’. The faster metabolic rate of human males could explain why men have a shorter life expectancy than women, Ursula observed wryly, so ‘even if female ensoulment is delayed for 7 weeks, women would seem to be amply recompensed by the expectation that the reverse process of the soul’s departure will be delayed by at least 5 years.’
In her own case, we can be grateful it was delayed much longer than that, for Ursula died in 2021 at the age of 97. She had been active, sociable, and intellectually engaged to the end. Even at the age of 97 with her failing memory, she still read textbooks on brain wiring and Mendel. Few lives were better spent.