During the nineteenth century, animal and plant taxonomists and anatomists were high-profile scientists who played to a public that was mesmerised by the continuous discoveries of remarkable flora and fauna in the new world, not least in Australia. Think John Gould, Sir Joseph Banks, Sir Richard Owen, Baron Georges (Mammoth) Cuvier, Étienne Geoffroy St-Hilaire, Jean Baptiste Lamarck, and Johann Meckel. None of these scientific heavyweights could afford to ignore Australia and its unique fauna. In particular, they could not ignore the Platypus, and many formed strongly held views about whether the Platypus was a mammal, a reptile or something altogether different, and about its mode of reproduction – did it produce eggs; if so, did they hatch inside or outside the body; did it suckle its young? All were frustrated by the inability of colonial naturalists and scientists to provide specimens capable of solving these burning questions. For example, John Gould lamented that ‘after an interval of 55 years we are still imperfectly acquainted with its habits, economy and the mode of its reproduction’. Meckel and Owen were able to demonstrate that the Platypus does have mammary glands, but not teats, but the question of egg-laying remained open. Owen encouraged New South Wales Surveyor-General Major Thomas Mitchell to capture a female Platypus every week between the months of September and November (the predicted breeding season) – ‘100 would not be too many’. Mitchell, preoccupied with inland exploration, was unable to deliver. At the Australian Museum in Sydney, Curator Gerhard Krefft offered the princely sum of £50 for a Platypus egg delivered to his door.

However, it took a young Scottish scientist, William Caldwell, sent to Australia in 1884 on a newly established Cambridge University travelling studentship, to apply a modern, scientific and professional approach to the problem. Caldwell travelled to the Burnett River in Queensland (where he was also interested in that other ‘living fossil’, the lungfish) and, by enlisting the help of the local Aboriginal people, captured literally hundreds of female Platypuses, and hundreds of its fellow Monotreme, the Echidna. Caldwell eventually found a female Platypus which had just laid an egg and had another in the cervix ready to be laid. He immediately sent a famously concise telegraph to the Dean of Science at the University of Sydney stating ‘Monotremes oviparous, ovum meroblastic’ – four words that, when read to a meeting of the British Association for the Advancement of Science the following week, reverberated through the zoological world like few others before or since. His message was that the Platypus did indeed lay eggs, and that the eggs resembled those of fish, reptiles, and birds in that the yolk-sac is large and essential for nourishing the conceptus, and only cells on the surface of the yolk-sac divide to form the embryo, rather than nutrition being derived mostly from a placenta, and the entire zygote dividing, as in marsupials and eutherian mammals (a holoblastic ovum).

While all this debate was raging, the shy and beguiling Platypus was quietly going about its business in the streams of eastern Australia and Tasmania, doing a remarkably good job of surviving the trashing of its riverine environment by Europeans. Little known and seen only by those who are keen enough to watch quietly and immobile at dusk, Platypuses still live within fourteen kilometres of Melbourne’s CBD. Indeed, they are still found in most streams within their original distribution, though they have long since been lost from the lower reaches of major streams in the Murray-Darling Basin, where the flow régimes bear little resemblance to the natural condition because of the dominance of the needs of agriculture.

Nine years after its first publication, eminent science historian Ann Moyal has produced an updated edition of her Whitley Award-winning book. It is much more than a history of this singular species. Moyal ranges far and wide across the history of natural science over the past two centuries to skilfully weave together the multiple scientific strands that led ultimately to an understanding of where the Platypus fits on the evolutionary tree, and what that means for our understanding of vertebrate evolution. This is Moyal’s great strength: her deep knowledge of the history of the natural sciences in Australia, combined with an ability to engage the reader while clearly presenting complex concepts and information. This second edition differs from the first only in that a new and important final chapter has been added to convey critical new information derived from the sequencing of the entire Platypus genome during the last decade.

A spin-off from the Human Genome Project is the application of its technology to other species in order to gain new understandings about evolutionary relationships. Because the Monotremes were thought to have arisen at the very base of the mammalian evolutionary tree, they were among the first group of animals targeted for gene mapping following the mapping of the human genome. An international collaborative effort began in 2004 and culminated in a conference in Victor Harbor, South Australia, in late 2008. The gene mapping project provided clear evidence of the early divergence of Monotremes from the reptilian stem, some two hundred million years ago – the deepest evolutionary history of any mammal. Among the many important findings summarised in the final chapter are that the Platypus retains genes that have been lost in reptilian and therian mammal evolution, and so allows a form of genetic time travel. Its sex chromosomes number ten rather than the usual two in mammals and more closely resemble those of birds and reptiles. There are other significant insights, too numerous to list here.

In his foreword to the proceeding of the conference, Professor Roger Short colourfully described the Platypus as ‘a one-holed wonder from Down Under’. Ann Moyal’s captivating words help us to understand why this is so and how we came to this understanding.