Mutations are mostly useless. Look at children of Hiroshima. Small useless arms etc. Even if it was useful one specimen cannot change a whole species. He would have to screw millions.
Yeah, that's a pretty extreme example of a mutation. Yes, most are entirely useless, but natural selection means that the useful ones do get passed on. They are also tiny changes.
Yes. One in thousands or millions. Not enough to displace the existing animals. If one in 10 lions were born with significant increased strength all over the world, yes mabe.
Once these changes happen, they don't just go away... They are passed on to children and spread throughout the population. Thus, minuscule changes propagate themselves and persist.
Only if the improved gene is propagated faster. If not the gene will remain miniscule as the old genes keep going.
