Re: Is the ocean halibut a case of 'bad' evolution?

Scientist try not to use words like "bad" and "good." I suspect you know that, and that's why you put quotes on the word. To humans, the halibut and flounder might look ugly, with its eyes on one side of its head, so that when it lies on the ocean floor on its side both eyes are up. But to another halibut they might find beauty in this.

Mutations do accumulate slowly over time, so the change in the DNA genome of organisms changes slowly over time. All primates are ~95% identical, and all mammals are something like 85% identical in gene sequences. The genotype changes slowly. However, the phenotype (what we look like), can change very rapidly. All dogs are a single species and are ~99.5% identical in genotype, yet a Great Dane looks very different from a Beagle. This is because there are certain genes that can change the looks of an organism drastically - the growth hormone gene, for example. It is likely that Great Danes and Beagles both produce the very same growth hormone protein, but the Great Dane produces a tiny bit more of it. A single base change (the genome of a mammal has about 3 billion bases in it) in the growth hormone promoter could make it increase the production level.

I don't know how long it took the halibut and flounder fish to change from being an upright fish, to swimming on their sides. Only the fossil record, or maybe DNA sequence analysis, can tell us that. Fish have been around for a lot longer than mammals, so it might have taken more time for an upright fish to evolve into a side-swimmer than it took for amphibians to come out of the water, evolve into mammals, and return to the ocean as seals and whales. The flounder may appear ugly and not well-designed, but that does not mean anything about how long it took to evolve.

It has more to do with the difficulty in changing basic designs, like overall body plan, than in changing minor details like size. All animals from worms on up that lineage have what is called bilateral symmetry (top and bottom, right and left, front and back) instead of just being round like a yeast cell or radial like a jellyfish or starfish. The halibut had to change one side into top. That's a huge change, not easy to do. It would certainly be less ugly if it had flattened out to swim with it's true belly on the floor, rather than turning on its side.

Brian