A question about transitional forms.. Somebody knowledgeable in evolutionary studies, please help...

Question

I am really confused about transitional forms..

When a reptile transforms to a bird, there should be transitional forms with the wings started to grow but not developed enough for the purpose of flying. This should continue for millions of years till the wings are fully grown. Isn't this against the law of natural selection?

I could never see reconstructed pictures of such transitional forms with incomplete wings.. could someone give me a link?

Answer 1

The first two answers are exactly correct.

A wing doesn't have to be able to produce full flight to nevertheless be useful.

For an example, have you ever watched a chicken run?   It cannot fly, but as it runs it flaps its wings, which makes it lighter and more agile, able to hop up onto objects many times its own height, or glide down from objects as high as a rooftop without injury.   Imagine an entire suborder of the dinosaurs (the intermediates between reptiles and birds), slowly getting smaller, with lighter bones, bigger hearts, developing feathers for warmth (since the dinos were warm-blooded), and using agility as their means of survival ... the ability to run quickly from predators, or chase flying insects by running and flapping onto low branches, or gliding down from higher ones.    Bit by bit the wings got better as the running and flapping, led to hopping, gliding, soaring, and eventually full-fledged flight.  

This is why it doesn't violate natural selection ... because the final function as we see it today does not have to be *complete* before it is useful.   It can develop and improve by incremental steps.

For information about the reptile-bird transitional forms, see:

http://www.talkorigins.org/faqs/comdesc/...

Answer 2

The issue is that the "proto-wings" need not neccessarily be used for flying, but could be used for a number of other purposes.

They could be used for display, or for gliding over short distances.

The wikipedia article on the origin of birds gives a decent primer:

http://en.wikipedia.org/wiki/Origin_of_b...

Answer 3

Most of the proposed hypotheses are just that, because there are few fossils to back them up. Squirrels and birds seldom fossilize because forest soil is acid and dissolves bones.

Two working hypotheses have been proposed "from the ground up" and "from the trees down". I think the second one makes more sense but that's just my uneducated opinion. Both state that a feathered limb could assist in making controlled leaps, which became glides, which became flight. If a flying squirrel fossilised, we'd have a hard time realizing that the beast is a glider, because its limb bones are 'normal' for a squirrel; it's the skin flap that gives it the edge. It's the same with the fossils we have - there could be some structure that would explain the issue, but we're missing it.