Taz writes:
Actually, no. All features are transitional features. Or one could argue that there is no such thing as transitional features because the term itself refers to an "in-between" feature, and there is no such thing.
The very term was conjured up by creationists as a strawman trying to diverge attention away from real science. They want people to believe scientists believe there were once upon a time half an eye, half a leg, etc.
The earliest use of "transitional form" and "transitional variety" that I can find is from a book not renowned for its creationist bent - 'The Origin of Species', by one Charles Darwin:
quote:
As natural selection acts solely by the preservation of profitable modifications, each new form will tend in a fully-stocked country to take the place of, and finally to exterminate, its own less improved parent or other less-favoured forms with which it comes into competition. Thus extinction and natural selection will, as we have seen, go hand in hand. Hence, if we look at each species as descended from some other unknown form, both the parent and all the transitional varieties will generally have been exterminated by the very process of formation and perfection of the new form.
But, as by this theory innumerable transitional forms must have existed, why do we not find them embedded in countless numbers in the crust of the earth?
—Charles Darwin
...and so on. I've been unable to locate the origin of the specific term 'transitional feature', but it's used commonly in scientific publications.
Not all features are transitional. A transitional feature would be one that is morphologically intermediate between primitive and derived members of a group. Archaeopteryx's tail could be said to be a transitional feature, since it combines traits that are primitive to Theropoda (long chevrons) and derived traits of birds (feathers).
The peacock's tail, on the other hand, is not a transitional feature. There's no more derived tail we can point to, for which the peacock's tail would stand as a good intermediate between it and primitive birds' tails.
Edited by caffeine, : No reason given.
Edited by caffeine, : To add the quote from Taz