One of Haeckel's earliest proponents was Carl Gegenbaur at the University of Jena (1865–1873), during which both men were absorbing the impact of Darwin's theory. The two quickly sought to integrate their knowledge into an evolutionary program. In determining the relationships between "phylogenetic linkages" and "evolutionary laws of form," both Gegenbaur and Haeckel relied on a method of comparison. As Gegenbaur argued, the task of comparative anatomy lies in explaining the form and organization of the animal body in order to provide evidence for the continuity and evolution of a series of organs in the body. Haeckel then provided a means of pursuing this aim with his biogenetic law, in which he proposed to compare an individual's various stages of development with its ancestral line. Although Haeckel stressed comparative embryology and Gegenbaur promoted the comparison of adult structures, both believed that the two methods could work in conjunction to produce the goal of evolutionary morphology.