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.
Read more about this topic: Dollo's Law Of Irreversibility
Famous quotes containing the words proposed, exceptions and/or law:
“The proposed Constitution ... is, in strictness, neither a national nor a federal constitution; but a composition of both.”
—James Madison (1751–1836)
“For true poetry, complete poetry, consists in the harmony of contraries. Hence, it is time to say aloud—and it is here above all that exceptions prove the rule—that everything that exists in nature exists in art.”
—Victor Hugo (1802–1885)
“The law is simply expediency wearing a long white dress.”
—Quentin Crisp (b. 1908)