Dollo's Law of Irreversibility - Proposed Exceptions To Dollo's Law

Proposed Exceptions To Dollo's Law

Although the exact threshold for violations of Dollo's law is unclear, there are several case studies whose results dispute the validity of some interpretations. For example, many taxa of gastropods have reduced shells, and some have lost coiling of their shell coiling altogether. According to S. J. Gould's interpretation of Dollo's law, it would not be possible to regain a coiled shell after the coiling has been lost. Nevertheless, a few genera in the slipper snail family (Calyptraeidae) may have changed their developmental timing (heterochrony) and regained a coiled shell from a limpet-like shell. Other proposed exceptions to this law include the wings of stick insects, the larval stages of salamanders, lost toes in lizards, clavicles in non-avian theropod dinosaurs, and neck, pectoral region, and upper limb musculature in primates, including the lineage leading to humans.