Why is it that in a gene sequence, some regions are highly conserved, while others are not? Please Help!

I have to know the answer to this for my bio final.

Thanks

The highly conserved regions are regions that encode vital domains in the protein, for instance, DNA binding regions, catalytic domains, allosteric binding sites, etc. or otherwise important for proper structure.

The nonconserved areas are parts of the proteins that link together the different domains such as loop structures.