In Dean Hamer's The God Gene he defines the God gene. He states in an interview:
"The God gene refers to the idea that human spirituality has an innate genetic component to it. It doesn’t mean that there’s one gene that makes people believe in God, but it refers to the fact that humans inherit a predisposition to be spiritual--to reach out and look for a higher being."
The book is an easy and quick read. It is mostly summary of recent scientific work. He takes issue with Daniel Dennett but a more substantial examination would be necessary to really glean anything of value from the disagreement.