Originally posted by: CottonRabbit
Well in the case of bird flight: feathers probably first developed on dinosaurs as insulation or as mating displays, then some small dinosaur with feathers became tree dwelling, then these feathers may have turned out to be good at letting them move more efficiently between trees by gliding, then natural selection began selecting for lighter and more aerodynamic dinosaurs that could glide better, and after millions of years, these dinosaurs/birds begin to actually be able to fly.
Of course there are other hypotheses on how this happened, but all probably center around how existing features in a dinosaur population became selected to fit a new adaptive behavior and slowly this behavior became flying. The previous gliding/jumping, while not as efficient as flying, did confer some sort of fitness advantage to the population.
Also, the experiment described in this thread kind of addresses your concerns. In this case e-coli made its huge change actually in 3 steps. The first 2 steps were relatively neutral, and would seem useless if evolution stopped then. But this population still kept this variation because it wasn't harmful enough to be selected against.
Your post raises new questions, though, for example if feathers could become such a randomly developing and persistent feature, why we don't see more oddness in, say, humans with 6 or 7 fingers, which also seems 'harmless enough not to be weeded out'. Sure, we do occasionally have a mutation there, but nothing like the sort of regular feature that might turn into more like feathers in above.
Anyway, I'd like to note another analogy with evolution, how some artistic areas seem to have analogous issues of evolution. Those of us who have played computer games for a while know how the 'art form' has evolved, with new paradigms providing incremental improvement to the earlier ones, how at first merely interacting with text, or moving graphics on the screen, were amusing, leading through a lot of phases; you could not see World of Warcraft, regardless of hardware technology, developed early in gaming.
It applies to other areas, too, like rock music; and we particularly note when someone makes one of those 'jumps' in evolution, notably in rock for example when the Beatles released the Sgt. Pepper album in an era of light pop, and many people saw the rock music art differently after (with psychedelics helping the mutation
).
Similarly, in movies, a genre like 'film noir' was invented by experimentation in one film.
Similarly, after centuries of straightforward oil painting, the surrealists mutated.