Quote from unretired:
Much ... especially early development in family and culture.
Adopted children from different cultures speak the language of
the culture they grow up in and don't have an accent.
There are many an adopted child who have grown up speaking "Valley Girl" speak
who's biological lineage have lived on the other side
of the world for thousands of years.
So perhaps one can conclude that beliefs are primarily an environmental product and hence much of what a person believes is rather inconsequential since it cant be much dissimilar from the source.