The planet we live on is positively crawling with life. There is not a nook or a cranny, it sometimes seems, where we don’t find some odd species of worm, some crawling slime or microscopic organism. Again and again, we drill or submerse or dig and we find new kinds of life, farther down than we thought possible, colder than we thought possible, hotter, more acidic, weirder.Every one of those plants and animals and prokaryotes and whatnot—every single one of them—came into existence from another of their kind. Some reproduce sexually, some by budding, some by division, but all from a parent organism more or less identical to them. As we run backwards in geological time, however, this great chain of living things must have had some first beginning, some origin, that did not involve a parent of the same—or indeed of any—species. Living things, now, may all come from parents of one sort or another, but life itself had, once upon a time, an absolute beginning. Matter that was utterly nonliving somehow turned into matter that was now living. Perhaps just once or at any rate not often, but one time at a minimum, somewhere and somewhen in the cosmos, a living thing must have just come into existence. Pop.But this is a very new way of thinking. From antiquity to the Middle Ages, from Aristotle on past Vesalius, Galileo, Newton, and after even Darwin, it appeared that this kind of thing, life from non-life, happened all the time. Maggots, famously, but also eels, bees, mice and sometimes even people—think about that—just sprang into existence from putrefying, dead matter. True, the list of organisms took some hits over time, eventually whittling down to just microorganisms or a few parasites like liver flukes, but the idea that life could come from non-life, regularly and routinely, was a remarkably hard one for us to shake.Why is that?

This book argues that one of the main reasons is that the evidence for spontaneous generation is, when you look hard at it, really quite good. There is a reason spontaneous generation was a fact for so long: it stands up to testing—and very, very good testing—remarkably well.By diving in to the debates around spontaneous generation as they unfolded historically, this book raises some important philosophical questions about what it means to do science, to understand nature. From its earliest articulation in Aristotle, all the way to the end of its plausibility as a fact about the world, we find that the problems posed by spontaneous generation provoked some very good, very hard thinking about what life was and how it could possibly come to be from nonliving matter. This is no easy problem, in fact. This story is emphatically not one of primitive thinkers failing to see the simple evidence, the easy tests (just cover the vials! Just boil the solutions!), right before their eyes. Not at all. Instead what we find is a long series of remarkably intelligent approaches to the evidence for spontaneous generation, struggling to figure out which animals might come to be in this way, and even more importantly: How?