how does mutation and variation lead to evolution?

Answer 1

This was the weak point in Chuck Darwin's theory of evolution. He said that variation led to" survival of the fittest". This is assuming that
the variation is a beneficial one. Many variations are caused by mutations (both gene and chromosomal). The problem with mutations is that almost all are harmful or lethal. Dead organisms generally don't reproduce very well!
I suppose that some nearly insignificant/minor variation caused by mutation could be beneficial and passed on to the next generation (?).

Answer 2

A mutation changes a gene which results in a change in some structure. Most changes are negative and the animal dies or becomes less adaptive. If by chance that change is positive, then it might provide the animal with an advantage. By having a variable population, there is an advantage to that species since certain variations might be more adaptive.

Answer 3

Mutation causes variation. Variation allows the variety which is more suited to cope with the environment to strive, while any varieties which are less suited will not. That variety which does the best will survive longer and grow a larger population, eventually choking the other varieties out.