Caveman invents God

[Riselka]

I'm asking this for someone on another website. This is what he wrote:

Looking for a book I read years ago. About an archeological dig. But the main premise of the book was about a caveman who couldn't deal with the death of his son so "invented" god. I have tried every google search. All help appreciated.

He read the book in the early 80s ... if that helps at all.