 In discussions with other members of Cambridge’s Theoretical Biology Club, Joseph Needham sought a theory of the chemical nature of the “organizer”. Building on D’Arcy Thompson’s theories of biological form and insights from biochemistry, he conceptualized fields as spatial regions of a developing embryo, which determine for all points within a region a specific quality, direction, and intensity. The field as a whole exhibits (in)stability and equilibrium positions. Organismal development is thus defined as