Almost every single one of these features is an
Atavism. An
Atavism is the apparent reversion of an animal back to an
ancient form. They normally occur when
dormant genes are turned on to when a
mutation in a
gene causes the animal to develop the
gene coding of an
ancient relative.
There have been many incidents of
atavisms recorded throughout history, all the way back to the time of
Caesar. They have long been considered
unimportant oddities. To some they were seen as a reminder that previous
imperfections lay just below the surface.
Stephen J. Gould claims something else entirely. He contends that they teach an important lesson the potential result of
small genetic changes.
Atavisms support the belief that
phenotypes can change rapidly with one or two small changes unlike the standard
gradualist model of evolution where many small changes are needed over generations.
Genetic systems contain extensive, hidden components and capacities for expressing small changes as large effects. That these components exist is the only way for
atavisms to exist. He feels that these components, which have possibly been hidden for millions of years, would allow for
rapid evolutionary changes and
adaptation.
Another example of an
atavism could be some
Flightless Beetle’s wings. The wings are fully developed, but the cover on the backs of the beetles became fused to its shell at some point in history, rendering it
flightless.
Atavism is a theory presented by, among others, Gould. It does not explain the unlikelihood of 1/3 of horses in a later German test study having the ancient gene, and the other 2/3 that had 3 toes having the 3rd toe duplicated. Also, as
melknia says, the probability that the same gene mutates everytime these fairly common
atavisms come up is fairly low.