Jack Cohen
Reproductive biologist, ‘alien creature designer’ and co-author of the Science of Discworld series
JACK COHEN, who has died aged 85, was a reproductive biologist known for his theory of why men produce so many redundant sperm; he was also well known in the sci-fi world as an “alien creature designer” and as the co-author, with Sir Terry Pratchett and Ian Stewart, of four Science of Discworld books which used the setting of Pratchett’s cult fantasy terrain to explain the real science of our universe.
Cohen first met Pratchett in the 1980s when he accidentally spilt a pint of beer over Pratchett’s lap at a science fiction convention. The friendship was subsequently sealed at a convention in The Hague, at which members of an audience of sci-fi fans objected when Pratchett, seeking to defend a fellow author who had earned their hostility, pointed out that he and his co-guests were so rich they did not need to attend such conventions, but were doing so out of the goodness of their hearts.
“Someone threw a tomato and it got him,” Cohen recalled. “Terry lost it. ‘What the f--- do you think you’re doing,’ he said, and really went over the top. I stood up and said ‘shut up’. I was at the back right of the audience and all eyes turned towards me. I said, extemporising wildly: ‘Money is like air and love. If you’ve got it, it doesn’t matter. If you haven’t got it, that’s desperate.’
“Everyone stood up and clapped and Terry said: ‘Is that Jack Cohen? Then I’ll buy you a drink.’”
As their friendship developed Cohen introduced Pratchett to his friend Ian Stewart, a professor of mathematics and colleague at Warwick University, with whom he had written several books including Figments of Reality: The Evolution of the Curious Mind (1997). Together they developed the idea of publishing works of popular science based on Pratchett’s Discworld, where everything runs on magic.
The premise of the Science of Discworld series is that the wizards of the Unseen University have accidentally diverted a dangerous overload of magic to create a containment field that keeps magic out and runs on the laws of physics.
When they start to poke around this strange new mini-universe, the wizards set off the Big Bang, initiating a speeded-up billion year spree through our own cosmic laws as they examine Earth – “the Roundworld” – from its early beginnings to the possible end of
terrestrial life. Alternating chapter by chapter with Pratchett’s Discworld tale, Stewart and Cohen explained how the laws of physics form and mould life, the universe and everything.
The first three books, The Science of Discworld (1999), The Science of Discworld II: The Globe (2002) and The Science of Discworld III: Darwin’s Watch (2005) all entered the Sunday Times bestseller lists, the third making it to number one. The final book in the series, The Science of Discworld IV:
Judgement Day, was published in 2013, two years before Pratchett’s death from Alzheimer’s disease.
Jack Cohen was born on September 19 1933 in Norwich and grew up in Stoke Newington. His grandfather was a rabbi and though Cohen lost his faith he continued to attend synagogue for cultural reasons.
After taking a degree in Zoology at what is now Hull University, followed by a PHD in feather pigmentation, he went on to do postdoctoral work at the University of Birmingham where he was appointed lecturer in the Department of Zoology and Comparative Physiology in 1959.
After a year at Harvard Medical School in 1967-8, he returned as a senior lecturer to Birmingham, where he remained until 1987, his students including the future Nobel Prizewinner Sir Paul Nurse. Later on, from 1996 to 2000, he was a consultant at the University of Warwick to both the Biology Department and the Mathematics Institute, where he became an honorary professor.,
In the 1960s and early 1970s Cohen developed and published his theory of sperm redundancy in which he sought to explain the enormous variation in numbers of sperm offered for fertilisation by different animals. This theory predicted that there would be more sperm “redundancy” in organisms with more “chiasmata” – developmental “cross-over events” in which chromosomes trade parts and during which errors can occur.
The number of such events differs between species, from none in the honey bee to about 50 in many mammals, and Cohen reckoned that in humans the chance of an error occurring is so huge that only one sperm in a million might be suitable for fertilisation. A corollary of this is that females must have effective systems for detecting and rejecting defective sperm.
Although the theory remains contentious (it does not answer the question why the development of an egg in the female does not involve the same risk of error even though it involves similar “cross-over” events), from 1987 to 1989 Cohen worked as a senior adviser on embryology at a private infertility clinic in London and, from 2000 to 03, as a consultant embryologist in the Assisted Conception Unit at Birmingham Women’s Hospital, where he and colleagues established a unit for investigations of sperm-associated infertility.
As well as numerous scientific papers Cohen wrote textbooks including Living Embryos – an Introduction to the Study of Animal Development (1967) and Reproduction (1977). He was a Fellow of the Institute of Biology.
His interest in reproductive biology fed into his fascination with science fiction and he worked as a consultant for television shows and sci-fi writers on the creation of plausible aliens and alien ecosystems.
In Evolving the Alien (2002, with Ian Stewart), an account of how extraterrestrial life might evolve, he distinguished between “universal” features of Earth life, and “parochial” ones. Eyes, for example, have evolved independently in many different ways, so appear to be universal. But having two eyes above a nose and mouth is a parochial feature derived from our fishy ancestors. Aliens are just as likely to have the mouth parts of a butterfly.
He and Stewart also published two sci-fi novels of their own, Wheelers (2000) and Heaven (2004), in which the aliens were presumably authentically evolved. Their other collaborations include The Collapse of Chaos: Discovering Simplicity in a Complex World (1994).
Cohen was a member of Mensa and his hobbies included “boomerangs” and “the maintenance and breeding, in captivity, of tropical fishes and reptiles, and the design of teaching and domestic aquarium and vivarium systems.” When Terry Pratchett found his pet terrapins were getting so fat on Kitkat bars that they were unable to retreat fully into their shells, he handed them over to Cohen to work off the weight.
In 1999 when Pratchett was awarded an honorary degree by Warwick University, the sci-fi writer made Cohen and Ian Stewart “Honorary Wizards of the Unseen University” at the same ceremony.
Cohen was married three times and had six children.
Jack Cohen, born September 19 1933, died May 6 2019