Genes are what code for the traits of an organism. They are heritable, which means the offspring inherits at least some of the genes from the parent (in humans it is 50% of the genes from each parent).

When there is a population that has varying genes and varying traits that go along with those genes, there may be a difference in fitness between individuals because of that variation.

So this leads to evolution...
Genes are the heridiatary material of our body they consists of DNA i.e deoxy ribo nucleic acid which consists of character of parents i.e of mother and father .
when genes are carrying characters of parents it may have some variation s and these variations are known as mutation .
so at the time of fertilization genes which are present on chromosomes transfer the characters from parents to offsprings so it is known as hereditary vehicle .
in this way genes bring evolution because of such disturbance in DNA.