Re: what changes take place during evolution?

There is a small chance of a small change in DNA replication during both
meiosis and mitosis. This doesn't happen very often, but is enough, over
time, to vary the gene pool enough to create variety and change.

One thing to take into account is that evolution can occur without
mutation. The variety in the gene pool is enough to create a change in the
population.

Let us take an extreme example. There exists some breeds of dog which have
both short and long haired varieties (eg. Border Collie). This is caused by
variety in the gene pool and as there is no disadvantage to either, they
tend to both be around. However, let's say that global warming put the
temperature right up to Carribean proportions and beyond. The long haired
versions of the collie may suffer from exhaustion, overheat and may even
die. This affects their ability to breed and we may find that the short
haired version is found more often and the long haired one becomes rare or
extinct. 

This is evolution at work but required no new mutation.