Where are all the missing links?

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The argument seems to be that many fossils should display obvious signs of developing into something else whereas most seem to be perfectly formed for the task at hand.

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Which is a bad argument. Of course all known species are "perfectly formed for the task at hand" -- if they weren't, they would not have survived. Evolution must proceed through species that are "perfectly formed for the task at hand".-

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'Archeaopteryx' is posed as an example of the 'link' between reptile and bird....

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The very first specimen of Archaeopteryx was originally classified as a new species of dinosaur and put into a drawer and forgotten for a over a hundred years. It was only when the second specimen was discovered with very clear feather impressions that its bird nature was realized. If that doesn't scream "transitional" then I don't know what does.-

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...the fact it is much-debated seems to illustrate the apparent problem...

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Well, the apparent problem is that some people are set in their beliefs are simply going to deny anything that contradicts them.-

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...such 'demonstrable' links seem to be a relative rarity whereas we could expect there to be many of them.

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Why should we expect to see "many" of them? I would expect to see very, very few...and am pleasantly surprised that we have as many that we do.-

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Flight of any description would have been a major boon and presumably such a creature would have done very well.

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Flight itself is not going to pop into existence all at once. There are going to be intermediates on the path to flight which will not be flying creatures. These intermediates will have to have some sort of feature that is "perfectly formed for the task at hand" and yet be the type of feature that will be able to evolved further into wings. It is possible that these in-between states survived in relatively small niches. And even then, it is not automatically guaranteed that the species will continue to evolve into flying creatures -- evolution does not proceed with a goal in mind. It is possible that the in-between "gliding" features (like the flying squirrel?) may be such that no further evolution into wings is possible. It may be that further generations will exhibit other characteristics that ensure survival that will take the species down another path, away from flying.But it does seem that flying is a boon once established. Insects, especially beetles, are the most ubiquitous group of animals known. Birds are also very successful. Among mammals, the most successful order is *ahem* Chiroptera, the bats.

Bats, flying lemurs, and primates share a common ancestor that they do not share with any other group. So it is probably a safe bet that the non-flying ancestor of bats were arboreal, and so flying probably developed from a gliding transitional form. In fact, the flying lemur is a "flying squirrel" type of glider.As far as birds, I don't know. I know I have seen pictures of the feathered ancestor of birds as arboreal, but I don't know whether there is direct evidence for this or whether it is a guess of the artist. At any rate, I assume that the non-flying ancestor of birds was arboreal and bird flight arose from gliding -- however, I admit this is just because I find it easier to imagine flight arising this way.But you are right -- unless some new finds have been discovered that have shed light on this, it is still a matter of conjecture why wings originally developed in birds.By the way, interesting fact -- molecular evidence suggests that two main groups of bats, the megachiroptera and the microchiroptera, are not monophyletic, and that these two lines may have developed flight independently.

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many species had bone structure (specifically the shape of the hips) identical to that of birds, while others still resembled reptiles.

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To be honest, though, this hip feature does not really count as a link between birds and dinosaurs since birds actually arose in the reptile-hip branch -- bird-like hips arose independently among the bird-hip dinosaurs and birds themselves.(Unless, of course, bird-hips are found among the saurischian theropods from which the birds arose.)

Oh yes indeed. I was just quibbling.

Hello, Ian.

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Would it be possible to form a chain from species so that a 1,2,...4..6.7..9...13,14,15... line of descent could be drawn through them?

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Biologists rarely make a "chain" of species indicating evolutionary relationships. That is because no one really knows whether a given species is truly ancestral of a later species or is simply another branch off of a common ancestor. Even when a species is labeled as "transitional", it is not meant to imply that the transitional is really ancestral. Any transitional is really thought of as another branching off of the common ancestor, maybe because it only branched off a very short time from the actual ancestor or for some other reason is thought to maintain enough primitive features that they are useful to give some idea of what that ancestor was like.For example, monotremes (the egg laying mammals) may be called "transitionals" for eutherians (placental mammals) and the pre-mammal ancestors. No one actually believes that modern mammals evolved from "monotremes" -- in fact, the split between the monotremes and other mammals occurred long, long ago -- back in the Triassic, I believe. But the monotremes have a mixture of eutherian and pre-mammal characteristics: they have hair and produce milk, like eutherians; but they do not have nipples, lay eggs with leathery shells, and have a single opening (the cloaca) for expelling feces, urine, and laying the eggs.Now, to your question. Scientists would not try to construct a linear evolutionary path for the animals that you indicated -- scientists almost never do that. What they would do is try to construct a phylogenic tree, that is a family tree; to use the characteristics that are apparent to determine the relative order in which the various lineages branched off from the rest. Maybe once this tree was constructed, they could then examine the various animals more carefully and try to determine whether any particular example was actually close to its branching point.

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The problem is Rahvin that different people have a different idea of "enough".

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Indeed. In fact, some of us don't need any fossils whatsoever. (But since we have them, they are pretty darn cool!)

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...I'm pretty sure that everyone understood that.

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Be careful of assumptions like that. Especially when talking to randman.

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"Okay, but do you have a picture of the bullet in flight?"

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"In fact, we do."

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"This bullet is in mid-air. Do you have one coming out of the gun?"

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Priceless.

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If there were no fossils of transitional forms at all then it would be a problem that would require explaining. This is based on the degree to which we do find fossils; if none were transitional then that would require some explaining.

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Just to clarify Ned's point a bit:If there was no fossil record at all, or only very few fossils known, then the lack of fossil tranistionals would not be a problem. After all, the fossil record was very sparse in Darwin's day, and yet he still managed to convince the majority of scientists of common descent. We would simply explain it by noting how rare fossilization is.However, fossils are not all that sparse -- we have bunches of fossils. In this case, if there were no transitionals at all we would, I think, have a bit of a problem.Also, this isn't entirely on topic here, but it is remarkable that all the fossil species known fit nicely into the current hierarchical classification scheme -- no surprises like mammal/bird chimeras. So this is two ways that that the fossil record supports the theory of common descent.

Sorry. That's what happens when I don't reread my posts carefully enough.

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the evolutionary theory requires creatures with partly formed organs.

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Here is an example of partially formed wings: Here is an example of partially formed legs: Finally, here is an example of partially form eyes: This is the sort of thing that the theory of evolution predicts.

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Or what about the transitions from simple invertebrates to the first vertebrates say the fishes ,,, tell me where do I go to see the transitional forms leading up to fish...

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Hello, Evopeach. If you don't mind, I'm going to pretend that you are interested in having a discussion on this topic and give you an answer to your question.As it happens, last night I was reading up on this very topic on the Palaeos website.Palaeos has a couple of nice short essays on the evolution of the first vertebrates going through more advanced vertebrates and up to the first fish. Note that the entire discussion is based on actual fossil transitionals.Actually this wasn't what I was really reading. What I was actually reading was the evolution from the lung fish ancestors to the tetrapods. Again, the discussion at Palaeos is based on actually transitional fossils.

Um, are you replying to my post? None of your post has anything to do with invertbrate to vertebrate evolution, nor to anything in any of the links I supplied.

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there is a growing body of evidence indicating that the appendix does in fact have a significant function as a part of the body’s immune system.

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I don't believe that any definite evidence for this has ever been provided; however, even if this is true it doesn't really address the main point. Why does this "immune function" require the appendix to be blind sac attached to the intestine? A blind sac that bears a remarkable resemblence, especially in its placement, to a functioning caecum in closely related primates? The appendix is a vestigial organ -- it clearly once had a function in the digestive process which it no longer has.Edited to add:Oops. I just realized that vestigial organs is off-topic here. I won't bother to reply to any responses to this post. Sorry.This message has been edited by Chiroptera, 15-Aug-2005 08:10 PM

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"The cradle of every science is surrounded by dead theologians as that of Hercules was with strangled serpents" -- T. H. Huxley

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Vestigial organs are great, becuase they have no use, and are clear representations of altered features. FLightless birds, with their vestigial wings (wings that often provide literally no purpose) are obvious evidence of common ancestry with burds that can fly.

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Be careful, Rahvin. Vestigial organs are not organs that have no purpose, but organs whose obvious original function has been greatly reduced or lost. I realize that you understand this, but Evopeach and randman are going to go out of their way to misread your post; no sense in giving them an even slight excuse for this.