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:
“It is not always possible to predict the response of a doting Jewish mother. Witness the occasion on which the late piano virtuoso Oscar Levant telephoned his mother with some important news. He had proposed to his beloved and been accepted. Replied Mother Levant: “Good, Oscar, I’m happy to hear it. But did you practice today?””
—Liz Smith (20th century)
“Skepticism is unbelief in cause and effect. A man does not see, that, as he eats, so he thinks: as he deals, so he is, and so he appears; he does not see that his son is the son of his thoughts and of his actions; that fortunes are not exceptions but fruits; that relation and connection are not somewhere and sometimes, but everywhere and always; no miscellany, no exemption, no anomaly,—but method, and an even web; and what comes out, that was put in.”
—Ralph Waldo Emerson (1803–1882)
“The great King of kings
Hath in the table of his law commanded
That thou shalt do no murder. Will you then
Spurn at his edict, and fulfill a man’s?
Take heed; for he holds vengeance in his hand
To hurl upon their heads that break his law.”
—William Shakespeare (1564–1616)