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:
“There never seems to be any difficulty in stretching the laws and the constitution to fit any kind of a political deal, but when it is proposed to make some concession to women they loom up like an unscalable wall.”
—Susan B. Anthony (1820–1906)
“Every declaration of love contains an unstated list of exceptions and demands.”
—Mason Cooley (b. 1927)
“But the creative person is subject to a different, higher law than mere national law. Whoever has to create a work, whoever has to bring about a discovery or deed which will further the cause of all of humanity, no longer has his home in his native land but rather in his work.”
—Stefan Zweig (18811942)