To see the quotes by Dr. Dean Hamer, and Dr. Byrd go to:
http://www.narth.com/docs/innate.html
I will check this out. It's extremely hard to imagine that some people have genetic machinery that causes them to believe in God, whereas others are barred from such belief by an accident of birth.
My conviction* is that the desire to know and love God is eternally established in the heart of every living being. Just gets very, very covered due to many factors (insert long philosophical/religious discussion later) - primarily because of long ago choices, and new wrong choices daily.
*Insert another discussion here. Will get back to this.