Hi Bolder-dash,
Given that we don't know everything and never will, there will always be questions for which we have few or no answers. Concerning examples of positive mutations in mammals, I'd be surprised if we know of very many. Mammals have very long generation times and very complex morphologies and functions, and mapping genes to morphology and function is a lengthy process. Random mutations are far more likely to be deleterious than advantageous. Their deleterious nature can be very extreme, even fatal, while their advantageous nature can be only subtlety incremental, and this is because large changes are bound to be bad.
But as Dr Adequate alluded earlier, population genetics tells us that mutation rates are consistent with evolutionary processes. This was all worked out in the 1920's, and it resulted in what is referred to as the Modern Synthesis, or the synthetic theory of evolution, which is the merging of genetics with the theory of evolution. Prior to the work of the population geneticists it was considered possible that genetics would not prove consistent with evolution, thereby bringing Darwinian evolution into question, but the research revealed that they reinforced each other. Your concerns that mutation rates are not consistent with evolution was addressed nearly a century ago.
Advantageous mutations are easier to identify in organisms that have a very short generation time. Some bacteria reproduce as often as every 20 minutes, but identifying advantageous mutations is still very difficult, because the advantage is usually very subtle. Identifying bacteria that look identical to all the other billions of bacteria but that reproduce 1% or 2% more successfully or that survive 1% or 2% more successfully is very difficult. That's why experiments often involve drastic environmental changes, because positive mutations can be identified simply by looking at bacteria that didn't die.
--Percy
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