Did God create other people besides Adam and Eve? After Cain killed Abel, he was cast away and said "whoever finds me will kill me", there he took a wife.

I think this indicates there were other people on the face of the earth created by God, but are there any other explanations?

The reason I ask this is that Adam and Eve are supposedly the couple that gave birth to all humanity, which I think is genetically impossible.
According to the Bible, God created no other people besides Adam and Eve.  Adam was created from the dust of the earth, while Eve was created from Adam (perhaps his rib).  

Genesis 5 indicates that Adam and Eve had quite a few children.  We have names for Cain, Abel, Seth, other sons (plural) and daughters (plural).  So, at a minimum, they had seven children.  If we assume that the birthrate for women is just equal to that of men, then Eve may well have had five daughters, pushing the total to ten.  The earth at that time was very fruitful, and people lived a very long time, so she may well have had more than that.

Genetically speaking, it is not impossible at all that one couple could give birth to all humanity.  Just because one scientist asserts something to be true does not make it so.  

See this article regarding skin tones and this article regarding a challenge to that claim altogether.