The origins of insect metamorphosis

Insect metamorphosis is a fascinating and highly successful biological adap tation, but there is much uncertainty as to how it evolved. Ancestral insec t species did not undergo metamorphosis and there are stilt some existing s pecies that lack metamorphosis or undergo only partial metamorphosis. Based on endocrine studies and morphological comparisons of the development of i nsect species with and without metamorphosis, a novel hypothesis for the ev olution of metamorphosis is proposed. changes in the endocrinology of devel opment are central to this hypothesis The three stages of the ancestral ins ect species-pronymph, nymph and adult-are proposed to be equivalent to the larva, pupa and adult stages of insects with complete metamorphosis. This p roposal has general implications far insect developmental biology.