Managing variation in the investigation of organismal development: problems and opportunities

This paper aims to clarify the consequences of new scientific and philosophical approaches for the practical-theoretical framework of modern developmental biology. I highlight normal development, and the instructive-permissive distinction, as key parts of this framework which shape how variation is conceptualised and managed. Furthermore, I establish the different dimensions of biological variation. Using the analytical frame established by this, I interpret a selection of examples as challenges to the instructive-permissive distinction. These examples include the phenomena of developmental plasticity and transdifferentiation, the role of the microbiome in development, and new methodological approaches to standardisation and the assessment of causes. In the light of these examples, the extent of variation exhibited by developing organisms and the questions that scientists increasingly ask concerning variation, I argue that it is no longer appropriate for the instructive-permissive distinction to underpin normal development. Furthermore, I argue that investigations into organismal development should investigate the effects of a wider range of kinds of variation. I close by examining various possible opportunities for producing and using normal development free of the assumptions of the instructive-permissive distinction. These opportunities are afforded by recent developments, which include new ways of producing standards, and the ability to produce, store, and process large quantities of data.