hi Thomas,
Thomas wrote:real life wrote:Simply put, evolutionists use the similarity of structures in different species (homology) as 'proof' of an evolutionary link between them.
Yes, but they never base that conclusion on only one structure.
real life wrote:(It's a type of circular reasoning: Organism A and organism B have similar eyes, therefore they are linked in the evolutionary process , i.e. they share a common ancestor or one evolved from the other.
Well, for one thing, independently evolved eyes often have structures different from each other.
Shouldn't they always?
Thomas wrote:For example, the eyes of octopusses have a different structure than the eyes of fish: octopus eye nerves come out on the outside of the eyes, while fish eye nerves come out on the inside first, then leave the eye on one single spot. (That's a problem for the "intelligent design" hypothesis by the way: wouldn't an intelligent designer make decide which side is "right", and stick to his decision?)
Why would we assume that different organisms living in different environments and facing different challenges would all best be served by the same design of each organ, etc ?
If that were so, the most logical arrangement would be to have one species of animal. Period. It would have the ideal design of every organ and none other.
It makes perfect sense for a designer to utilize multiple designs to meet various conditions, doesn't it?
Since a bear and a stingray live in different conditions, they need different features (one needs heavy fur, the other does not); and they need similar features (eyes, stomach, etc) customized for their situation.
Thomas wrote:Anyway, my point is that when genetically unrelated species evolve similar features independently, you can often see it in distinctive differences in those features.
Again, shouldn't that be always?
Thomas wrote:real life wrote:How do we prove that Organism A and organism B have an evolutionary link? Well, their eye structure is similar. )
This would be circular reasoning if taxonomist relied on one feature only -- but they never do. Even where evolutionary convergence has produced similar eyes, the animals will have differing features in other organs.
It is interesting to see you invoke 'convergence' to try to explain why homology is selectively and arbitrarily applied as a criteria, but it's not very convincing.