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:
“There is a distinction to be drawn between true collectors and accumulators. Collectors are discriminating; accumulators act at random. The Collyer brothers, who died among the tons of newspapers and trash with which they filled every cubic foot of their house so that they could scarcely move, were a classic example of accumulators, but there are many of us whose houses are filled with all manner of things that we “can’t bear to throw away.””
—Russell Lynes (1910–1991)