@fluterother
“What he said was not untrue, but it wasn’t very impressive either. When people try to explain how evolution gave rise to giraffes and to polar bears it reminds me of this story.”
I am wondering which explanations you have read or heard? Again, you haven’t given me much to go on as to exactly what is causing you problems. Could you give a specific example of an explanation of how giraffes or polar bears evolved that doesn’t work for you?
I’ll give it a shot with polar bears.
Not that long ago, in evolutionary terms- about 200,000 years ago- a group of brown bears were isolated by increasing glaciation in Siberia from the brown bear populations in the rest of what is now Russia. Most of them died- but a few survived.
In the increasingly cold climate, there was strong selection pressure for aspects that could help the bears survive in a glacial world. Genetic variation provided the raw material for nature selection to work upon. So those aspects- longer coat, whiter hair, ect.- became more common in the population. Those bears that had a survival-promoting variant had more surviving offspring, so the genes became more common. And thus the animal we now know as a “polar bear” emerged.
We see this transition in the fossil record. We start with Ursus maritimus tyrannous, which had the teeth and size of a brown bear. Over the next 20,000 years, fossils show progressively smaller body size and a more elongated skull with sharper molars and longer canines; better for feeding on seals.
And, even today, the separation is not total, as this is a very new species. Global warming has allowed the grizzly to wander further north than it had been able to for many millennia. Grizzlies and polar bears are now interbreeding, producing hybrid “grolar bears” that combine features of both parents- and that are fertile.
So, what about this scenario is unlikely or incomplete?