You seem to be conflating losing function with a reduction in fitness. That doesn't always have to be the case. Would the LRP5/MCM6 mutations that basically shut off an intolerance to lactose after weening be an increase or decrease in fitness? In cavefish, a mutation in the ND2 gene causes eyelessness. It's energy consuming to form and maintain eyes - and that energy is an utter waste if a being lives in a completely dark environment. Would not developing eyes in a completely dark environment be an increase in fitness or a decrease?
ND2
Evidence for Multiple Genetic Forms with Similar Eyeless Phenotypes in the Blind Cavefish, Astyanax mexicanus
I would say it shows that the eye is not a mutation, but has always been present, which is why kinds in isolated environments that do not need them still have the genes for them. Now that gene may then go dormant since it is not needed, but that gene was always there, and will always be there.
I guarantee you take those same eyeless catfish and raise them in a normal environment, and within several generations those genes for the eyes will be turned right back on, and eyes they will have once again.
No mysterious steps in the evolution chain, merely what genetics has taught us, that genes that already exist become dominant or repressed.
They have just now within the last decade learned to make genes dominate or repressed reliably to approx 4 genomes. They have made chicken embryos grow teeth as they develop, not by mutating genes, but by making what already existed in the genetic sequence dominate instead of repressed.
It didn't become something else, it merely turns off or on certain sequences, sequences that existed from the beginning. They like calling them separate species, as if that makes them of different kinds, But in the end they are still catfish.
Of course if you were consistent in your trees, they wouldn't be so confused.
Catfish:
Kingdom:
Animalia Phylum:
Chordata Superclass:
Osteichthyes Class:
Actinopterygii Subclass:
Neopterygii Infraclass:
Teleostei Superorder:
Ostariophysi Order:
Siluriformes
Cat:
Kingdom:
Animalia Phylum:
Chordata Class:
Mammalia Order:
Carnivora Family:
Felidae Genus:
Felis Species:
F. catus
So for Catfish you use the order name for kind, but in cats you place that at the Family level. And catfish you use the species name of where you place cats for the family name in catfish.
Siluriformes is then divided into family and then species. A little consistency would be nice now and then. Been trying to tell you, a cat is a cat is a cat, as a dog is a dog is a dog. And as a catfish is a catfish....
Just a little harder to tell those billions of fish apart, as it is for aves. Oh. but instead of family or order you have use the class name for kind with aves.
