THE CHEMICAL BASIS OF MORPHOGENESIS
đź“ś Abstract
It is suggested that a system of chemical substances, called morphogens, reacting together and diffusing through a tissue, is adequate to account for the main phenomena of morphogenesis. Such a system, although it may originally be quite homogeneous, may later develop a pattern or structure due to an instability of the homogeneous equilibrium, which is triggered off by random disturbances. Such reaction-diffusion systems are considered in some detail in the case of an isolated ring of cells, a mathematically convenient, though biologically unusual system. The investigation is chiefly concerned with the onset of instability. It is found that there are six essentially different forms which this may take. In the most interesting form stationary waves appear on the ring. It is suggested that this might account, for instance, for the tentacle patterns on Hydra and for whorled leaves. A system of reactions and diffusion on a sphere is also considered. Such a system appears to account for gastrulation. Another reaction system in two dimensions gives rise to patterns reminiscent of dappling. It is also suggested that stationary waves in two dimensions could account for the phenomena of phyllotaxis.
✨ Summary
The paper introduced a mathematical reaction–diffusion framework in which interacting chemical substances can destabilize an initially homogeneous state and generate spatially organized patterns. Turing analyzed the growth of perturbations using Fourier modes on a ring and spherical harmonics on a sphere, identifying stationary waves, oscillatory behavior, and other instability modes. He proposed possible biological interpretations involving Hydra tentacles, leaf whorls, pigmentation-like dappling, phyllotaxis, and gastrulation. The analysis also emphasized random molecular disturbances, differential diffusibility, nonlinear saturation, and the need for continual energy input in sustained patterns.
The work became foundational for mathematical and theoretical biology and led to the modern study of Turing patterns and reaction–diffusion systems. Later research extended the framework to developmental biology, chemical pattern formation, mechanochemical models, and other physical systems. Reviews document applications and extensions in chemical experiments and biological morphogenesis, while commentary has also described influence in areas including geomorphology and other pattern-forming systems. (pubmed.ncbi.nlm.nih.gov)