tronvillain

Thanatos:
Let's ignore that question for a minute and think about what would be necessary to turn a dog into a bat. Compare their genomes, which at the most basic are a linear sequence of four different nucleotides. Now look at the types of mutations which are known to occur. It now becomes obvious a path between the two genomes can easily be traced between the two sequences using known types of mutation. Of course, in order for this to actually occur naturally, every genome in the sequence must at least produce a functioning organism, and natural selection and genetic drift must drive the process forward (or at least permit it to eventually wander in the right direction). I think you should be able to answer your own question now.

trunks2k

That's still kind of vague definition of type.... But anyways.. No a single dog is not going to grow wings. Evolution doesn't work like that, nor does it sya it does. Evolution doesn't greatly change the characteristics of a single animal. It works on the animals of group as a whole, and can take many, many generations to produce any sort of noticable change. IS it possible for a group of dogs to eventually grow wings? Theoretically yes. But the bone/muscle structure would have to change so much that it isn't likely to be possible that there is a set of enviromental changes that would lead the dogs to becoming streamlined, walking on two legs (so the front legs can change to wings), and some sort of change in DNA to form feathers instead of hair, etc... etc... that would actually occur. Now since it's so unlikely for that to actually happen, will it always never happen? No. It can happen, but it would take an extremely large amount of time, and very special circumstances, which as I said, is unlikely. For all we know, some day modern day dogs will all suddenly die off, leaving no offspring.
Does that mean that no species was a common ancestor of both a bird and a dog? Absolutly not. The two "types" of animals are so different because they are the net result of millions of years of different, tiny, genteic changes and natural selection. At one point in time there was an animal that had a group of genetic changes that lead it down both the path to eventually turning into a bird and the path to eventually turning into a dog.
I don't think you understand how evolution works. Species don't suddenly sprout wings out of no where. Let's take a hypothetical situation to illustrate the most basic idea of how evolution works (this is completely hypothetical and is only used to illustrate a point, and is over simplified, so nobody flame me for not having the evoltuion of wings or birds correct):

Let's say you have a species of squirrles that, like most squirrels, live in trees. For the time being they are completely similar. But "one day" a change in the sperm of a father squirrle makes his offspring have large amounts of flesh draped from the wrist to the body of the baby squirrel. This new devolpment means the squirrel is able to glide somewhat from tree to tree. Meaning it can find food easier and escape predetors with a large amount of ease. Because of the advantage this squirrel has over the rest of his family, he's the first choice for mating. Thus eventually many more squirrels like him are born. And soon the squirrels population has a good mix of those capable and not capable of gliding. Over time new "advancments" are introduced to the gliding squirrels. By come chance, some of theses squirrels are born with a bone structure that allows the squirrel's arms to bend so it can glide faster and better. These squirrels are now prime mating choice. No remeber there are still squirrels that look like the original ones, and are perhaps having their own changes that allow them to surivive better. Slowly over time, the body of the gliding squirrels become more stream lineed, and the fleshy part that allows them to fly has started to gain bone support to facillitate easier gliding. By this time the gliding squirrels have become so different from the original type of squirrels and what those other squirrels had become, they can no longer mate with one another, thus you have new species.

That was really way way over simplified and I know I didn't talk about feathers, which is because the evolution of feathers is seperate from the above situation. But as I said, it's just to give a better idea of how new species come about. I.e. over long periods of time, not suddenly out of nowhere.

KeithHarwood

This is no different from the paper-and-pencil game where you have a word at the top of the page and a word at the bottom of the page and you have to change one into the other changing one letter at a time, with the restriction that all words in between be real words. This will establish that the transformation is possible.

However, in evolution there are fewer constraints.
Firstly, there is no word at the bottom of the page, when you reach the bottom of the page you have reached present day. Second, you are allowed to duplicate letters, subject only to the requirement that they remain real words; so that Woden (Norse god) can be followed by wooden. Thirdly, every time you create a new word you must put it at the top of a new page and continue on the new page as well as the original. Eventually you will end up with a large bunch of pages and at the bottom of one of them will be the equivalent of a mammal with wings. (And at the bottom of others, a mammal with fins, a mammal with paws, a mammal with grasping hands.)

KeithHarwood

Ah yes Harper's Magazine. One of the few mainstream scientific journals available at a newstand. And so much more authoritative than those scandal rags Scientific American or New Scientist.

tronvillain

Well, that's a slight improvement in the analogy, but it's still pretty innacurate. You have more than one "word", not all your "words" need to be real, etc.

KeithHarwood

Yup. You can extend the game in many ways. The important point, though, are, firstly, that the lines split to form a tree of derivations, there is no linear progression; and secondly, that there is no goal. I think the last is the reason why Creationists hate evolution; the purpose of creation was to create human beings. I suspect that Creationists understand evolution better than those people who think that the purpose of evolution was to create human beings.

Oolon Colluphid

Do you really mean ‘species’? How do you tell species apart, and is that what defines a ‘kind’?

Is the maned wolf the same ‘type’ as the grey wolf? Are African hunting dogs part of the dog kind? Are zebras, quaggas and Pliohippus of the horse type? Is the termite-eating aardwolf a hyaena, or something separate?

Straw man. No scientist is stupid enough to think so, though creationists are ignorant enough to think they do.

Sure. For a particular dog to. But dog ancestors didn’t evolve into birds -- they made their living differently -- small dinosaurs did. Try this:

Start with smallish bipedal predatory dinosaur. Let its descendants’ scales increase in size for thermoregulation. The scales trap air much like a mammal’s fur.

Let some descendants become tree-climbers, perhaps chasing prey up them, and/or themselves escaping predators. They jump from branch to branch. Sometimes they fall. Some break their necks and leave no descendants; some are saved, maybe only from low falls, by the air drag of their ‘fluffy’ scales.

Anything mutation that increases surface area will increase the height they can survive a fall from. Surface area becomes crucial, and is something that can increase incrementally. Let the surface area of the arms increase from generation to generation, as those with more leave more descendants. The surface area could be made of underarm skin, and especially the enhanced scales, which would be lighter than a bone-and-muscle construction of the same area.

Also, let some descendants put their upper limbs out when they jump, for balance or because those that do, again increase surface area should the balance side of it not come off. Those with more surface area leave more descendants, since they are better at jumping -- or rather, falling with style, as Buzz Lightyear would say -- between trees.

A flap of the arms in some descendants would give them an extra lift on take-off, and so it can fall with style further. A similar flap midway would carry those that do it right a bit further still.

Let the muscles that operate the arms’ downstroke increase incrementally, as the stronger ones which fall-glide further can get away from more predators and can catch prey by jumping at it from further away or above, ie unawares.

Let the muscle attachments at the sternum similarly increase down the generations, for the same reasons.

Let the hand shorten as the elongated scales increase. Let the creature flap more often....

The above is of course just a scenario. Oddly enough though, there is a whole range -- in date order -- of fossil creatures at various stages of just this sort of change. Here, for instance, is a feathered dinosaur:





Need I mention Archaeopteryx? How about Caudipteryx?

Even more oddly, birds possess the genes for <a href="http://www.devbio.com/chap06/link0601.shtml" target="_blank">making teeth</a>, and for <a href="http://www.mun.ca/biology/scarr/Hampe_experiment.htm" target="_blank">making theropod-like legs</a> with a full fibula and separate tarsals:



These genes are just never expressed in modern birds. Why would they have them, if not that their ancestors -- whence their genes -- had them?

Dunno. They can change what protein is produced, where it is used, and so alter how an embryo develops.... what do you mean by information?

TTFN, Oolon

[ April 18, 2002: Message edited by: Oolon Colluphid ]</p>

MrDarwin

How would you go about proving that a dog cannot grow wings?

Instead, let's use another "kind" of creature--dinosaurs. Restating the assertion ever so slightly,

A dinosaur cannot grow wings.

And, referring to Oolon's post, I wonder if this assertion holds up. It would appear that dinosaurs did indeed grow wings, and judging from the earliest winged creatures (whether you call them dinosaurs or birds) it would certainly seem that precious little "new information" was required, as the structure of the wing is nearly identical to the structure of the forelimb of a dinosaur.

Thanatos

If, as everyone on this site claims, we evolved through gradual mutations - why are there not a plethora of transitional forms in the fossil record?

Piltdown Man and Nebraska Man were frauds and Archaeopteryx, Ramapithicus, Australopithecus, Lucy, Homo Habilis, Homo erectus, and Neanderthal man - a few of which you have pointed to - DO NOT 'hold any water'.

Why doesn't the fossil record show life forms coming into existence in a slow and gradual process? I'll tell you why, because that's not what happened - even many of your evolutionist friends are now changing their views and are proponents of 'punctuated equilibrium'.

If mutations are random and often neutral, why don't we find a whole truck load of useless features on organisms?

The DNA similiarities between humans and chimps DOES NOT prove evolution. All it does is show that we have things in common with them. We have the same genes as almost every living thing - from potatoes to mice - so what, what does that prove? You can't use circular logic! Homologous structures are not proof of evolution.

Can dinosaurs grow wings? I don't think so - consider that either cold-blooded reptiles had to evolve into warm-blooded dinosaurs, or cold-blooded dinosaurs had to evolved into warm-blooded birds. As far as I know, the differences between cold blood and warm blood are so different that most evolutionists try and avoid the issue.

A few tidbits...

"It's biophysically impossible to evolve flight from such large bipeds with foreshortened forelimbs and heavy, balancing tails," exactly the wrong anatomy for flight. (A. Gibbons, "New Feathered Fossil Brings Dinosaurs and Birds Closer," Science, 274:720-721, 1996)

New research shows that birds lack the embryonic thumb that dinosaurs had, suggesting that it is "almost impossible" for the species to be closely related." (A.C. Burke and A. Feduccia, "Developmental Patters and the Identification of Homologies in the Avian Hand, "Science, 278(5338):666-8, October 24,
1997, with a perspective by R. Hinchliffe, "The Forward March of the Bird-Dinosaurs Halted?" p. 596-597; J.D. Sarfati, "Dino-Bird Evolution falls flat," Creation ex nihilo, 20(2):41, March 1998.)

"At the morphological level feathers are traditionally considered homologous with reptilian scales. However, in development, morphogenesis [shape/form generation], gene structure, protein shape and sequence, and filament formation and structure, feathers are different." (A. H. Brush, "On the Origin of Feathers," Journal of Evolutionary Biology,
9:131-142, 1996)

Mageth

What we have here is a Tired Old Argument Barfer and a Quote Flinger.

I'll only hit on one area related to an earlier post:

The DNA similiarities between humans and chimps DOES NOT prove evolution.

Of course not. I didn't say it did. It is, however, evidence that is consistent with evolutionary theory. DNA was discovered decades after Darwin jumpstarted the theory of evolution, and genetic evidence viewed so far, across many species, is consistent with evolutionary theory (and, indeed, improved evolutionary theory by filling in some gaps) and further illustrates the mechanism by which traits are modified/inherited (you could say genetic evidence is as predicted by evolutionary theory).

All it does is show that we have things in common with them.

No shit. Common descent, common ancestors. Evidence consistent with the theory of evolution. And as I said it also shows a mechanism for descent with modification.

We have the same genes as almost every living thing - from potatoes to mice - so what, what does that prove? You can't use circular logic!

More evidence for common descent.

You and your proof thing. What circular logic? The genetic evidence is remarkably consistent with other (fossil, morphological, etc.) evidence. One is not used to prove the other.

Homologous structures are not proof of evolution.

No, just more evidence consistent with evolutionary theory!

[ April 19, 2002: Message edited by: Mageth ]</p>