In 1937, the evolutionary biologist Julian Huxley was contacted by a male fan who wanted more than an autograph. ‘Dear Sir,’ he wrote. ‘Would you consent to being the father of my wife’s child, possibly by artificial insemination?’ Most people would have baulked at such a request, even if the ‘possibly’ hinted that he might not have had to use a turkey baster, but it seems that Huxley took it in his stride. That may be because at the time he was a prominent member of the Eugenics Society, the aim of which was to improve the human race through selective breeding, though it could also be explained by his family’s history.

Julian’s grandfather was Thomas Henry Huxley, nicknamed ‘Darwin’s bulldog’, a combative defender of evolutionary theory who enjoyed arguing with his enemies and would probably have picked a fight with himself were nobody else around. In one edition of Charles Kingsley’s The Water-Babies (first published in 1863), he had been depicted peering at a baby in a glass bottle, an image that evidently fascinated his grandson. ‘Dear Grandpater,’ the young Julian wrote. ‘Have you seen a Waterbaby? Did you put it in a bottle? Did it wonder if it could get out?’ By 1937, the image of the water-baby had become part of another popular fantasy: in Brave New World, the dystopian satire written five years earlier by Julian’s brother Aldous, we see ‘rows and rows of babies’ in ‘lovely clean bottles’ growing in an enormous hatchery.

In this book, Alison Bashford’s focus is on Thomas and Julian, who were photographed together in 1895, the young boy’s hand emblematically clasping his grandfather’s meaty paw. Both spent their professional lives trying to explain to the general public how humankind had evolved from monkeys and wondering what it might yet become. ‘We might even think of them as one very long-lived man, 1825–1975,’ Bashford imaginatively claims, ‘whose vital dates bookended the colossal shifts in world history from the age of sail to the space age; from colonial wars to world wars to the Cold War; from the time when the Earth was 6,000 years old according to Genesis, to a time when it was 4.5 billion years old, according to rock samples returned from the Apollo missions.’

Bashford’s title suggests that this book will provide an ‘intimate history’, but anyone who picks it up expecting a straightforward narrative is likely to be disappointed. The opening chapter provides some highlights of their lives – their pioneering work as scientists and public intellectuals; the key roles they played in organisations like London Zoo, UNESCO and the World Wildlife Fund – but thereafter Bashford’s study is arranged into thick thematic slices: Thomas and Julian’s shared fascination with animals, particularly birds and primates; Thomas’s popularisation of the idea of natural selection and Julian’s theoretical application of it to breeding programmes for humans; the painstaking efforts of both men to disenchant the world (Thomas coined the term ‘agnostic’) and expose spiritualists and pseudo-scientific hoaxers.

While this approach can make the chronology hard to follow, it also generates some illuminating parallels. Both Huxleys carefully curated their public images, Thomas by commissioning portraits and busts of himself that filled the family home with visible reminders of his success, Julian by making regular appearances on television and radio (he presented the first TV programme to be produced by the young David Attenborough and won an Oscar in 1938 for a short film called The Private Life of the Gannets). Both men would also have good cause to worry about their image were they alive today. Racism casts a long shadow across Bashford’s book. Thomas believed that the idea that ‘the negro is the equal of the white man’ was so ‘hopelessly absurd as to be unworthy of serious discussion’, while Julian in a series of articles on ‘the Negro Problem’ in 1920s America outlined his belief in a fundamental biological difference between black and white brains, adding that although equality of treatment was a reasonable goal, racial prejudice ‘was not without a good deal of sound social and biological instinct’. Later he went further still, claiming just two years before the inauguration of the Universal Declaration of Human Rights that ‘human beings are not born equal in gifts or potentialities, and human progress stems largely from the very fact of their inequality’. Bashford defends Julian’s reputation, pointing out that such views were hardly exceptional at the time, though even she seems to lose heart when she quotes a 1962 lecture in which he listed some of the ‘imperfections’ that a selective breeding programme would allow humanity to expunge, including colour blindness and ‘some kinds of sexual deviation’ (he also suggested that in the event of a nuclear war, ‘shelters for sperm banks will give better genetic results than shelters for people’).

Bashford includes some excellent stories about both men, ranging from the sublime (the young Thomas observing some luminescent sea creatures ‘shining like white-hot cylinders in the water’) to the ridiculous (Julian receiving a letter from ‘a good-looking male’, who had read one of the popular-science pieces published in Penthouse magazine, informing him that he saw ‘thousands of other men creeping away to eject their sperm over your articles, rather than read them’, such magazines being ‘merely our general insightment [sic] to National Masturbation and degradation’). The book’s generous length also ensures Bashford has enough space to rummage around in some of the stranger corners of her subjects’ lives. She discusses, for instance, a popular three-volume textbook that Julian co-wrote with H G Wells and Wells’s son in the 1920s called The Science of Life, in which a photograph taken during a séance of a head supposedly made from ectoplasm sits alongside an image of ‘hypnotized lobsters’.

Both Huxleys would have appreciated the breadth of Bashford’s research and her skill at explaining heavyweight scientific ideas with a light touch, though they might have baulked at some of her language. Her description of how Julian’s mother ‘passed to another world’ in 1908 would have puzzled Julian, who later pointed out that he ‘no more believed’ in ‘a world of departed spirits’ than his grandfather had done. A few other passages are similarly clunky: ‘Birds – and especially grebes – stuck with and to Julian for his whole life’; ‘As a family, the Huxleys had much love and death to withstand.’ Such lines call to mind the novelist Mary Augusta Ward’s remarks on an early article her nephew Julian published in the Cornhill Magazine: ‘There are a few sentences that seem to want combing out a little.’

The most moving parts of this book have less to do with science than with the reasons why both Huxleys sought refuge in its apparent certainties. When Thomas’s wife wrote to Julian in 1903, referring to their relatives as ‘the Happy Family’, her words may have stung, for it is hard to imagine a less happy family than the Huxleys. Thomas’s aggressive bluster hid a susceptibility to crippling bouts of depression – ‘Paroxysms of internal pain’, he called them. His father had ended his days in an asylum, ‘sunk in worse than childish imbecility of mind’, and his brother James, a psychiatrist, was supposed to be ‘as near mad as any sane man can be’. Julian himself was regularly placed in institutions, where he spent months of ‘paralysed inactivity’; in 1914 his brother Trev was found hanging from a tree in a nearby wood shortly after explaining that he felt ‘lost in a pit an enormous way behind my eyes’. It must have seemed that mental illness was being passed down the generations like a curse. If Julian’s correspondent had known more about the family’s troubled history, one wonders whether he would have wanted some of that Huxley sperm after all.