Dev Genes Evol (2011) 221:255–279 a characteristic and not necessarily vitalistic capacity of all organisms (Roux 1914). However, when it comes to mechanisms of self-regulation, Roux could not offer much. He mentions phenomena in the inorganic world which seemed to be examples of self-regulation to him. One of these examples is the flame of a candle. The flame has metabolism, it exists only through the flow and consump- tion of material and it regulates its size according to the supply. The other example is the regeneration of defects in crystals, which inorganic chemists had observed (Przibram 1906). What these examples have in common is the highly inhomogeneous starting situation. They do not provide instances for spontaneous pattern formation emerging from unstructured initial conditions. Such examples were virtu- ally non-existent when Driesch argued for his vitalistic view in 1899. In later years, Driesch was confronted with attempts of colloid chemists to provide physicochemical analogues for life. In 1896, Raphael E. Liesegang had published a paper showing that in a solidified gel containing potassium dichromate, the local addition of a drop of silver nitrate leads to the formation of ring-like precipitation patterns of sliver dichromate. Subsequently, Liesegang described mod- ifications of this experiment as ‘Emulation of life processes’ (Liesegang 1911a, b, c). Likewise, the French biologist Stéphane Leduc had shown that the interplay between precipitation of inorganic salts and osmotic growth produces complex morphologies. He called his experimental work ‘synthetic biology’ (Leduc 1912; for a famous description see Mann 1947, 22–24). While most of this early work on colloid chemistry left no significant traces in the history of pattern formation theory (Keller 2002, 15–49), Liesegang’s periodic precipitation patterns continued to attract the attention of physicochemists. A satisfactory mechanistic account, though, required the fully developed formalism of chemical reaction diffusion theory which would become available only much later (Flicker and Ross 1974). To date, the complex interplay between gel matrix, ionic properties of the electrolytes and speed of precipitation producing not only rings but also spirals and complex branching patterns is not fully understood (Sultan and Sadek 1996; Karam et al. 2011). However, neither at the time of their discovery nor in subsequent years did the Liesegang patterns contribute much to an understanding of biological processes. They have mostly been linked to geochemical phenomena such as banding patterns in minerals (Krug and Kruhl 2000). At the time of Driesch, though, many biologists had the hope that colloid chemistry provided a key to the secrets of life. Driesch himself was impressed by the complex patterns and shapes generated in the experiments of Leduc and Liesegang, but doubted their importance for explaining embryonic devel- opment with two convincing arguments: they lacked the 257 reproducible specificity of organic forms and the capacity to self-regulate (Driesch 1921, 80–82, 134). Driesch was also fascinated by D’Arcy W. Thompson’s monumental On growth and form (1917), a work which would become influential for all subsequent researchers addressing problems of morphogenesis and pattern forma- tion. Thompson extensively applied mathematics to prob- lems of biological form at all levels of organisation, but only in a descriptive and non-mechanistic way. ‘My sole purpose is to correlate with mathematical statement and physical law certain of the simpler outward phenomena of organic growth and structure or form…’ (Thompson 1917, 10). In Driesch’s view, Thompson’s geometric descriptions ‘provided only the general type of an arrangement’ (Driesch 1921, 80) or ‘the general frame for the process’ (Driesch 1921, 82). It could neither explain the specific arrangement nor the underlying generative forces. Had Driesch seen the later developments in molecular biology that addressed the problem of specificity and the rise of theories of self-organisation that provided models for self- regulation and scaling, I believe, he would not have voted for vitalism. However, these developments were only in their infancy in Driesch’s lifetime. The rise of physicochemical theories of self-organisation The history of biological pattern formation theory is indirectly linked to the discovery of self-organisation in chemical systems, which, in turn, is rooted in theoretical discussions and experimental findings on oscillating chem- ical reactions in homogeneous phase. This link, although indirect, has three ramifications. First, the most successful and influential early theories of biological pattern formation were based on chemical-reaction diffusion rather than physical (mechanical, hydrodynamic, electromagnetic) models. In the framework of these chemical approaches, there was no reason to believe that biomolecules within an organism would not obey the same laws of mass action and diffusion which apply to molecules in general. Therefore, whatever progress occurred in chemical kinetics could be used to compare and enrich biological theories. Second, conceptual problems to imagine how self-organising pro- cesses could occur on the basis of the known physical laws were not unique to biologists like Driesch. Many chemists in the first half of the twentieth century also believed that spontaneous emergence of temporal or spatial order in a homogeneous phase violated the second law of thermody- namics. Indeed, a broad acceptance of the possibility of self-organisation in biology was predated and prepared by the analysis of physical conditions allowing for temporal and spatial order to arise in chemical systems. Third, the communication between chemistry and biology was not