Distinction From Re-evolution
In some cases, it is difficult to tell whether a trait has been lost then re-evolved convergently, or whether a gene has simply been 'switched off' and then re-enabled later. Such a re-emerged trait is called an atavism. From a mathematical standpoint, an unused gene (selectively neutral) has a steadily decreasing probability of retaining potential functionality over time. The time scale of this process varies greatly in different phylogenies; in mammals and birds, there is a reasonable probability of remaining in the genome in a potentially functional state for around 6 million years.
Read more about this topic: Convergent Evolution
Famous quotes containing the word distinction:
“Let those talk of poverty and hard times who will in the towns and cities; cannot the emigrant who can pay his fare to New York or Boston pay five dollars more to get here ... and be as rich as he pleases, where land virtually costs nothing, and houses only the labor of building, and he may begin life as Adam did? If he will still remember the distinction of poor and rich, let him bespeak him a narrower house forthwith.”
—Henry David Thoreau (1817–1862)