Introduction: The Stickleback Model Frank A. von Hippel “With respect to reptiles and fishes,” wrote Charles Darwin (1871) in The Descent of Man, and Selection in Relation to Sex, “too little is known of their habits to enable us to speak of their marriage arrangements. The stickleback (Gasterosteus), however, is said to be a polygamist; and the male during the breeding-season differs conspicuously from the female.” With this introduction to the stickleback, Darwin set the stage for its development as a model organism in behavioural studies. And just one year after the publication of The Descent of Man, Darwin (1872) published The Expression of the Emotions in Man and Animals, which, along with his chapter on instinct in The Origin of Species (Darwin, 1859) launched ethology as a science by applying the ideas of natural and sexual selection to the study of behaviour. He concluded his chapter on instinct with a summary of his theory of natural selection, as applied to behaviour: “Finally, it may not be a logical deduction, but to my imagination it is far more satisfactory to look at such instincts as the young cuckoo ejecting its fosters-brothers, — ants making slaves, — the larvæ of ichneumonidæ feeding within the live bodies of caterpillars, — not as specially endowed or created instincts, but as small consequences of one general law leading to the advancement of all organic beings, — namely, multiply, vary, let the strongest live and the weakest die.” Darwin used the comparative approach with both his animal and hu- man subjects. The co-discoverer of natural selection, Alfred Russel Wallace, wrote in his review of Darwin’s book on the expression of emotions (Wal- lace, 1873): By means of a series of questions sent to correspondents in various parts of the world, Mr. Darwin has ascertained that many well-known modes of expression are almost universal. Even such an apparently conventional action as the shrug of helplessness or apologetic refusal has been ob- served among various savage races. Being thus proved to be natural, not © Koninklijke Brill NV, Leiden, 2010 Tinbergen’s Legacy in Behaviour, 3-11 4 von Hippel an acquired, expression, it becomes necessary to account for it, and this is done on the principle of antithesis; every part of the expression being the opposite of that which implies determination and action. Comparatively few human expressions, on the other hand, can be distinctly recognized in animals, that of sneering by raising the upper lip on one side, and thus showing the canine teeth, being one of the most curious. The technique of comparative biology, as established by Darwin, was taken up by Niko Tinbergen. It was Tinbergen who built upon what was al- ready a good body of work on threespine stickleback (first described by Lin- naeus in 1758 as Gasterosteus aculeatus, which means ‘belly bone spined’) and made them a model in ethology. Tinbergen’s book (1951), The Study of Instinct, marked a critical achievement in the maturation of ethology as a scientific enterprise. In it, Tinbergen illustrated his vision of ethology with comparative examples from throughout the animal kingdom, but with special attention paid to threespine stickleback. Of the 210 pages of text, threespine stickleback appears on 42 of them, as well as the photo plate opposite the ti- tle page. The highly ritualized behaviour of the stickleback appealed to Tin- bergen’s penchant for experimentation. The stickleback responded well to models, and this discovery gave rise to a flurry of experiments using dummy males and females. The ease of maintaining stickleback in the lab also ap- pealed to Tinbergen, for here was an animal that could be studied in natural and artificial environments. Tinbergen’s reliance on the stickleback and his other favourite species led one reviewer to write, “In its current stage, ethol- ogy resembles a patchwork quilt, pieced together with bits of stickleback, wasp, cichlid, duck, herring gull, etc., the whole seeming to cover the real- ity better than any theory thus far advanced” (Greenberg, quoted in Kruuk, 2003). Three years before the publication of The Study of Instinct, in 1948, Tin- bergen founded the journal Behaviour to serve the burgeoning field of ethol- ogy. The first issue of the journal included Tinbergen and van Iersel’s (1948) classic paper, “‘Displacement reactions’ in the three-spined stickleback.” By the time Tinbergen received the Nobel Prize in 1973, his former students, such as Jan van Iersel, Piet Sevenster and Desmond Morris, had greatly ex- panded the utility of the stickleback model through their discoveries in the behaviour of the reproductive cycle. The threespine stickleback’s role as a model organism expanded beyond the confines of ethology in the 1960s and 1970s to include morphological.