Internalism, externalism and life-cyclism in the history of helminthology

The history of helminthology in the Early Modern Period has been characterized as a debate between two camps, the internalists and the externalists. The internalists believed that helminths are spontaneously generated within the body of the host, whereas the externalists claimed that helminths enter the host from the external environment. According to the this account, the debate between these two camps ended in the nineteenth century with the victory of the externalist viewpoint. Here, we redefine these two terms, as well as the beliefs that the two groups upheld. We suggest that internalists were not necessarily committed to the theory of spontaneous generation, nor were externalists committed to its rejection. These terms only refer to the place where helminths supposedly originate, but not to the process by which they are generated. Thus, some internalists rejected the theory of spontaneous generation, while others held externalist viewpoints and at the same time accepted this theory. We claim that the debate did not end with the victory of the externalist camp; rather, a new position which we call "life-cyclism", emerged and incorporated some elements of the two earlier positions.