Babble from the Religious Front

[DPDarkPrimus]

Don't know specifically about the dolphin, but marine mammals like whales and dolphins would have had ancestors which left the ocean, became land animals and then went back into the water. This explains their inability to breath underwater, since they lost the water breathing ability when they went on land. They couldn't simply regain the water breathing ability, since evolution doesn't go backwards (or rather the probability that an animal would favour going in a "backwards" direction is less than the more numerous "forward" directions ).

Thus they has to go through "descent with modifications", and the species which became marine animals would have to modify themselves to allow them to live in the water in other ways (such as being able to hold their breaths for long periods). I believe the whales are actually closely related to cows. This is derived from molecular biology, where we count the mutations in various genes. The less number of mutations, the closer the relation.

I just think that there has to be some other reason as to why they have no water breathing abilities, . . . . . if they came out of the water for a period of time, first they would have to develope the means TO survive outside of the water, but to say that it would be "de-evolving" for them to return to the water and reform water breathing abilities again, when they obviously had reason to return to the oceans, that's where I don't follow the logic. It would seem to be a better survival tactic to regain the abiblity to breath underwater if that's where you again reside. . . . . . . rather than having to take gulps of air every so often.

They did not "de-evolve" when they returned to the water. There is no such thing as "de-evolution". They evolved traits that were similar to their water-based ancestors.

Sure, it'd be better for them to have gills... there's an argument AGAINST an intelligent designer right there.

[Einhander Sn0m4n]

Isn't that called 'convergent evolution', DPDP?

[Lord of the Abyss]

Actually, I rather doubt a mammal could ever evolve gills; breathing water would suck the body heat right out of the animal. That's why seagoing mammals have thick layers of blubber, after all; there would be no way of preventing heat loss in an oxygen exchange organ due to the massive surface area involved.

[mr friendly guy]

Actually, going in a 'backward' direction is favored in the short run -- that's what we keep a lot of our junk DNA for. However, once the shape of the network has changed, it becomes tremendously unlikely to take steps backwards.

(in other words, they have a very short 'undo' stack)

Yes you are right. Evolution can go "backwards" in the short term. I was of course simplying it for him. In any event the whale's evolution did not go backwards.

[mr friendly guy]

I just think that there has to be some other reason as to why they have no water breathing abilities, . . . . .

Such as.. If you can't come up with some hypothesis, your argument essentially becomes an argument from incredulity.

if they came out of the water for a period of time, first they would have to develope the means TO survive outside of the water,

They did. They evolved to breath in air as opposed to water.

They also developed features which will allow them to go on land as which we can see by their vestigial features.

From talk.origins

Modern whales often retain rod-like vestiges of pelvic bones, femora, and tibiae, all embedded within the musculature of their body walls.

Whales also retain a number of vestigial structures in their organs of sensation. Modern whales have only vestigial olfactory nerves. Furthermore, in modern whales the auditory meatus (the exterior opening of the ear canal) is closed. In many, it is merely the size of a thin piece of string, about 1 mm in diameter, and often pinched off about midway. All whales have a number of small muscles devoted to nonexistent external ears, which are apparently a vestige of a time when they were able to move their ears - a behavior typically used by land animals for directional hearing.

The diaphragm in whales is vestigial and has very little muscle. Whales use the outward movement of the ribs to fill their lungs with air. Finally, Gould (1983) reported several occurrences of captured sperm whales with visible, protruding hind limbs. Similarly, dolphins have been spotted with tiny pelvic fins, although they probably were not supported by limb bones as in those rare sperm whales. And some whales, such as belugas, possess rudimentary ear pinnae - a feature that can serve no purpose in an animal with no external ear and that can reduce the animal's swimming efficiency by increasing hydrodynamic drag while swimming.

but to say that it would be "de-evolving" for them to return to the water and reform water breathing abilities again, when they obviously had reason to return to the oceans, that's where I don't follow the logic.

They don't "de-evolve". If they could do that, they would somehow regain gills and become amphibians then fish again.

It would seem to be a better survival tactic to regain the abiblity to breath underwater if that's where you again reside. . . . . . . rather than having to take gulps of air every so often.

It is a better tactic. However, evolution doesn't work like an intelligent designer. It can't grasp what would be a better tactic the same way you just did.

It only modifies what is already there. As I explained earlier, its difficult to evolve backwards because there is only one "backward" path versus numerous "forward" paths ie every other possible path. This becomes more difficult in the longer run as the backward path becomes longer ie you must lose more features which allowed you to survive on land.

[wolveraptor]

Actually, going in a 'backward' direction is favored in the short run -- that's what we keep a lot of our junk DNA for. However, once the shape of the network has changed, it becomes tremendously unlikely to take steps backwards.

(in other words, they have a very short 'undo' stack)

Example: Titanis, the phorusracid (sp?) that developed two claws similar to, but more devloped than, the tyrannosaurids. The existing bone structure was sufficient to "re-evolve" such a system.

[drachefly]

Reviewing what I said, I want to make it clear that I don't mean that the 'junk DNA' is only good as an undo stack, but also good for recombining with newer elements, as just suggested.