Different in degree or kind: Egnor's take; more on gaps (Introduction)

by dhw, Sunday, October 23, 2016, 08:25 (2954 days ago) @ David Turell

dhw: My hypothesis, in line with the cases we know of, is that environmental conditions caused organisms to make the changes. Here’s a website explaining the advantages of primitive lungs, which obviously have a long history.

1. How did fish evolve lungs? - Quora
https://www.quora.com/How-did-fish-evolve-lungs

DAVID: Sorry, but I've read your article, which is filled with Darwin-speak. A swim bladder is a swim bladder, not a lung. Evolution to lung is assumed. Where is the provable research? Not in fossil evidence.

They categorically inform us that the swim bladder evolved FROM (not to) a primitive lung. It is the primitive lung that is my focus, not the swim bladder.

QUOTES: Lungs are homologous to the swim bladder of bony fish. However, it's not that lungs simply evolved from the swim bladders of fish; in fact, the reverse is true.
The swim bladders of bony fishes living today, like the lungs of terrestrial vertebrates, are both exapted from primitive lungs.
(To put it another way, terrestrial vertebrates specialized in using these primitive lungs for breathing, while sea-bound bony fish specialized in using it for buoyancy, but the original organ probably served both purposes, to different degrees.)

But I am only quoting this to show that the primitive lung has a history which is always associated with environmental needs. Among the functions listed are enhancing stablility in the water, filtering carbon dioxide out of the bloodstream, oxygenating the blood in hypoxic environments, I don’t know why this should be dismissed as Darwin-speak (whatever that means). I find the link with environmental needs at least as convincing as the hypothesis that your God gave a particular fish a set of almost readymade lungs (just one transitional phase apparently) before it stepped onto the land.