There are some sequence disimilarities in the two
accounts, and in G1 it is implied that a whole race
of men and women were created rather than just the
Adam and Eve of G2.
My (dispasionate) opinion is that these two chapters
represent the creation myths of two different clans that
joined at some point. The myths were then combined into
one explanatory text (possibly with a few minor mods to make
them fit better) in order to bind the clans more closely
together.