I understand natural selection, except the source of variation, which i understand is random mutations, but isn't it quite unlikely that beneficial mutations appear at random a lot more than they would? If we were to trace the evolution of man from the first mammal which looked pretty much like an opossum, there are a thousand specific characteristics our primitive mammal must acquire in the course of it's evolution till homo sapiens. Say, a primitive mammal does receive a beneficial feature like better eye sight, but how does that feature spread from just one mammal to an entire species, are all species results of a few generations of inbreeding? I'm just confused, i'm not questioning whether evolution happened. It did, as it is evident from fossils, geographical distribution and all.
Added (1). please suggest me a good book that explains this in detail if you can
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