what is a transitional form?

Question

what evidence do they provide towards the theory of evolution??

Answer 1

A "transitional form" is a way of interpreting the fossil record, and a response to people arguing that there are "missing links" in the fossil record. Technically, *all* species are transitional, because everything is always evolving. But when we look back in hindsight at the fossil record, it is sometimes convenient to say that a certain fossil represents a transitional or intermediate form between an ancestor and a descendant.

The more complete the fossil record for a certain species or genus or family, the more of these "transitional forms" can fill in the details of what structures evolved in what order and when, and what it looked like. The fact is that many organisms (e.g. bony fishes, horses, humans, whales, elephants) have very nicely filled in records with many transitional forms provide strong evidence of the general process of evolution. But the lack of a complete fossil record for a specific organism is not evidence that this specific organism did not evolve from any ancestor at all.

A metaphor I like to use is that it is like tracing the development of a child through a photo album that you are filling in. You might have a photo of the child at 3 and another one at 8. When you find another photo of the child at 6 years old, you can see a "transitional form" of the child (his exact appearance at age 6). You can infer from all these pictures what he looked like at age 5. But the lack of a photo at age 5 is not evidence that the child was never 5 years old at all ... or that all the pictures are of different children (provided the similarities and tell-tale features indicate that they are all the same child in development).

--- P.S. ---

And hey, Spock. It's considered a bit dishonorable to simply copy somebody else word-for-word without crediting them. When you copy-paste from wikipedia you should say so ... or better yet, rather than just copy-paste the text, provide a link to the page so that people can have the benefit of all the hyperlinks and illustrations on the wiki page.

Here's the wikipedia page Spock copied from (I highly recommend it ... and click on the 4 illustrations on the right, showing the filling in of "transitional forms" in the human fossil record):
http://en.wikipedia.org/wiki/Transitional_fossil

Answer 2

People have found fossils in the ground that looked like modern stuff (like a horse), and also fossils that look like nothing at all that's around today (like a trilobite). So, theoretically, if all present life can be explained in terms of past life, there must be things in between ancient life (like a trilobite) and modern life (like a horse) that has some characteristics of both. And things in between those, and so on and so on. So that eventually, if you found enough fossils, it should show a progression of how life changed through the eras to give rise to different new species which eventually replaced all the old ones. Some people call those things in the middle 'transitional forms'.

I don't like the term, though, because it implies that it's half something and half something else. Which it's not. Turtles aren't half hyper-turtle (or whatever it is that turtle progeny might evolve into), they're completely adapted in their own right to whatever's going on right now.

Not to mention the suggestion that evolution may not always work in a sense of gentle, progressive changes, but instead occasionally making huges leaps of many simultaneous changes.

But let's not confuse the issue. If you found a 'transitional form' - a species that had some characteristics of an extinct animal and some of a living one - it would demonstrate a means by which evolution might have occurred. Evidence!

Hope that helps!

Answer 3

A transitional fossil is the fossil remains of a creature that exhibits certain primitive (or basal) traits in comparison with its more derived descendants. "Missing link" is a popular term used for transitional forms. According to modern evolutionary theory, all populations of organisms are in transition. Therefore, a "transitional form" is a human construct that vividly represents a particular evolutionary stage, as recognized in hindsight.


When Charles Darwin's The Origin of Species was first published, the fossil record was poorly known, and the claim that there was a lack of transitional fossils was perfectly reasonable; indeed, Darwin stressed in his work that this lack was the most formidable obstacle to his theory. However, the discovery of Archaeopteryx only two years later was seen as a triumph for Darwin's theory of common descent. Gaps remain in the fossil record, however; and while some argue that this is a problem for evolutionary theory, most scientists accept that the rarity of fossils means that many extinct animals will always remain unknown.

Though the evolution of the horse and its relatives, as Othniel Charles Marsh assembled surviving fossils in his reconstruction of the evolution of horses in the form of a single, consistently developing lineage with many "transitional" types, is often cited as a family tree with a number of clear transitional fossils, modern cladistics gives a different, multi-stemmed shrublike picture, with many dead ends: see evolution of the horse. Other specimens cited as transitional forms include the "walking whale" Ambulocetus, the recently-discovered lobe-finned fish Tiktaalik, with many tetrapod characteristics, and various hominids considered to be proto-humans.

Answer 4

it's like the 'missing link'
it's the evolved form of a creature that isn't the primitive form, but isn't the fully evolved creature, either.

they provide evidence for evolution when fossilized transitional forms are found near the 'before' and 'after' forms

Answer 5

A transitional form is something like being in evolutionary phase to reach the final stage. For instance in case of butterflies from cocoon to moth to butterfly and in case of frog from tadpole to frog.