 A field is organized from center to periphery, with a focal point of maximal intensity and gradual decrease from this center. This organization entails a “physiological gradient”: a robust distribution of (molecular) properties, which vary along the three spatial dimensions and along one or more axes (polarity). Its causal activity is holistic, determining cell behavior, which in turn produces growth, differentiation, and morphogenesis. Haraway (1976), Keller (2002), and Vecchi and Hernández (2014) examine the complex and uneven history of gradient and field concepts in developmental biology. Haraway, as discussed above, is concerned primarily with these concepts as metaphors structuring the organicist paradigm via the work of Harrison, Needham, and Weiss. Evelyn Fox Keller considers these concepts as part of the (so far largely unsuccessful) tradition of mathematicizing biology to understand development. Davide Vecchi and Isaac Hernández elaborate on Keller’s view, arguing that the concept of “morphogenetic field” was supplanted by Wolpert’s concept of “positional information”, part of the mid-twentieth-century theoretical shift from organicist ideas to genetic control of development (see  Section 8.3).