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 a man find himself, in distinction from others, on top of two wheels with a chainat least in a poor country like Russiaand his vanity begins to swell out like his tyres. In America it takes an automobile to produce this effect.”
—Leon Trotsky (18791940)