“So it was that one night in May 1904 on board the research ship Thor, while fishing for cod alevin in the Atlantic to the west of the Faeroe Islands, we caught an eel larva in a net that had been pulled up close to the surface.” This is how the oceanographer Johannes Schmidt describes the event that would revolutionise contemporary knowledge of eels. We now know that the eels that live in European fresh water breed in the Sargasso Sea, about six thousand kilometres away from the spot where Schmidt saw the larva. We know that they must swim for seven to fifteen years before reaching they waters off the shores of Scandinavia or Morocco, where they will live until the time comes for them too to make the journey back to their traditional breeding ground. The lives of eels, made up of long-distance journeys and metamorphoses, seem so adventurous that they have often been described as sagas. In this book, the author, an expert in his field, describes the most fascinating stages in the eel’s biological cycle, its migrations and the modifications it undergoes during its life. Eels interest us not only because of their life and breeding cycles, but also because of the questions they raise concerning our ideas about evolution. Is there an explanation for their strange behaviour? Does the notion of adaptation suffice to explain everything the eel has become? Doesn’t a living creature maintain a certain amount of independence in relation to the world that surrounds it? Isn’t adaptation triggered and informed as much by internal demands as by the action of the environment?

Yves-Alain Fontaine is an honorary professor at the Museum of Natural History, in Paris. He is the author of Sentimental Evolution.