The importance of spatial structure in biology.

Living things are highly complex and organised. This is often taken as an objection to reductionism and a point in favour of organicist views, which argue for the central role of the organism in all biological explanations. This paper argues that biological organisation often either is, or depends on, spatial structure, together with interactions among parts of the system understood in physical terms. We take spatial structure to include position, configuration, shape, directionality, and orientation of objects in space. Important features of the spatial structure of living systems include physical boundaries, such as membranes; cellular structure, which includes physical objects spatially arranged in certain ways; directionality and orientation with respect to internal and environmental signals; location, both of organisms in their environments and of components within the organism; and shape, including the shapes of organisms and their components at atomic, mesoscopic, and larger scales. The importance of spatial structure for explanations of the functioning of biological systems corroborates criticisms of genetic and molecular reductionism, but is compatible with physical reduction - the explanation of biological phenomena in physical terms - and part-whole reduction - the explanation of systems in terms of their parts, spatial structure, and interactions with each other and their environment.