The whole purpose of sex is to mix things up, genetically. That's the engine of the modifications.
As far as the fossil record, we sometimes see a clear series of transitional forms and sometimes not. Finding any fossil at all is remarkable.
Darwin knew little of the mechanisms of evolution and certainly nothing of genes. He described natural selection, which, in a stable environment, is, in fact, a slow process. He knew nothing of faster mechanisms.
Mixing up pre-existing useful advantages- you are using the example of merely tweaking a parameter that determines coat length, and hence you have pretty much a 50 50 shot at a change that is least hypothetically advantageous right?
An analogy being, you can hit three random keys on a piano and have a good chance at hitting a chord that sounds nice- given that the piano is already precisely tuned for that purpose
while 3 totally unguided random frequencies have effectively a 100% chance of sounding horrible
So micro v macro is a big deal, there IS an inherently fundamental difference.
It was very compelling, intuitive to note that classical physics perfectly described an apple falling from a tree- so why not extrapolate this out to account for all physical reality?
why not write off the concepts of mysterious unpredictable underlying forces, specific parameters, highly specific blueprints guiding it all- as the realm of religious idiots?
Those idiots were absolutely correct in their objections to classical physics, and for exactly the right reasons. Simple laws cannot account for the complexities of physical reality- which would instantly collapse under those laws, into the simplest homogeneous state those laws alone describe. Simply adding a lot of time and space for simple laws to work, just creates a lot of nothing for a long time
So the devil is in the details, I admit there is no slam dunk super intuitive case here,
wanted to say a bit about fossils to- must do that later- for some reason I don't get your alerts?