 This “epigenesis-first” view of development set the stage for a strand of theorizing that continued well into the twentieth century. The main theoretical tension in twentieth- and twenty-first-century studies of development is not between classic preformation and epigenesis, but between different views about control of developmental processes. If genes are the primary source of control, then organismal development is preformationist in an important sense: it is genetically determined. But if control is more distributed or holistic, such that developing organisms are (in some sense) self-organizing, then the process is regulated in a way recalling classic theories of epigenesis. Several influential theories of morphogenesis and pattern formation take the latter view. Gene-based accounts of development take the former. In this way, the classic theoretical opposition between preformation and epigenesis is transformed and carried forward into the twentieth and twenty-first centuries. In the first half of the twentieth century, theoretical concepts associated with epigenesis played a significant role in studies of development. This section surveys the main theoretical efforts along these lines.