One of the consequences of global warming is reduced final body sizes in animals of different orders, mainly in aquatic ectotherms like fish or water-breathing invertebrates. In this article, we identify August Pütter (1879–1929) as the originator of what is now called the “temperature–size rule” and as the first physiologist to develop a mechanistic explanation for this phenomenon. While Pütter’s growth model was indirectly influential through its adaptation by Ludwig von Bertalanffy (1901–1972), his explanation of the influence of temperature on (...) growth remained either unknown or misunderstood. In this contribution, we reconstruct the theoretical framework of his model and compare it to recent critiques of mechanistic models on growth and temperature. As we argue, Pütter’s theory of “similarities of growth” provides explanations for observed temperature–size patterns trends that avoid later accounts of underlying “biological laws.” While recent findings suggest that some aspects of Pütter’s model need revision—for example, the proposed exponents of the anabolic and catabolic terms in his growth equation—we argue that his mechanistic model was designed in a way that could account for the multiple apparent exceptions to the temperature–size rule that were recently found. (shrink)