Why do you say that? My understanding is that there are a couple of things involved in species differentiation, one that a beneficial mutation occur and that it happen in a somewhat isolated population. The only thing that is required for a mutation to be beneficial is that it grant some survival capability in a particular niche.
All you need to do is look at what is causing the benefit. There was a mutation in Lenski's experiment where the propulsion mechanism of the E. Coli simply didn't exist. The "bugs" who had this mutation didn't waste any energy on producing the flagellum. The reason this was a benefit is that the medium the "bugs" were in was constantly vibrated so the food sources would get to the E. Coli that didn't have a way to swim. This is clearly a beneficial mutation but obviously not something that you could extrapolate out into the formation of new biological functions.
You need more than benefits to make a microbe turn into man. It doesn't matter how many generations you wait.
Given more and more time life has a chance to experience more mutations and the same species being more frequently isolated by changes in the environment. Genetic material is preserved only when handed down to the next generation, so it's really a matter of odds, according to the theory. The fact that most mutations are detrimental or fatal doesn't affect things.
Lets say there is a truly beneficial mutation that is extremely rare 1 in 10^20 organisms any other mutation on that same chromosome comes along for the ride.
Detrimental mutations, no matter how numerous are weeded out and favorable ones, no matter how rare, tend to be preserved. Add in the enormous time scale involved and you can see change in the fossil record.
That isn't true. Look at humans, mutations are accumulating and selection can't keep up. You also need to look at H1N1 flu virus that has undergone
multiple extinction events over the last 100 years. It comes back because some pocket of the dormant virus gets exposed and reintroduced. They go extinct because of genetic meltdown because detrimental mutations build up.