'The species problem is a vexing and important one, and John Wilkins has done more than anyone else to dig into its history and integrate it with philosophy past and present. Thus he was the perfect author for this book, which is a wonderful, accessible entryway to the diverse set of issues bearing on why species have been such a 'thing' for 2000 years. My own conclusion is to follow Darwin and acknowledge the species rank is a meaningless human construct - the full tree of life is what matters, not just the single level within it arbitrarily called species. But to decide whether to agree with me or not, you need to absorb the content in this book.' Brent D. Mishler, author of What, if Anything, are Species?, Distinguished Professor of Integrative Biology, University of California, Berkeley