Evolution of the human

Just wondering about the whole evolution theory.
I thought that we require genetic variables in order to survive as a species as in if i mate with my family or close relatives it would cause problems in the genes (inbred issues)

We must have started out in a very tiny number somewhere down the line - how did we get the genetic diversity in order to survive i juts dont get it.

Either way you look at it science says we eveolved or the bible sais adam and eve i think both are wrong but im just a mere mortal - what do you people think.