I think Peterson believes that religiosity is an evolved trait that served to promote human cooperation. Due to selection pressure the groups who were able to cooperate based on shared narratives out competed groups who could not. Eventually, all people did it intuitively. He believes religiosity is a useful heuristic to conduct social behaviour in society. When asked if he believes in god he will respond “I act as if he is true”.
For a contemporary example, you and I both enact the narrative that money is true. It doesn’t take much critical thought to realize that money is a fiction but as long as we act as if it is true we humans can cooperate on massive global scales. Other social mammals need to know each other intimately in order to cooperate but human beings do not. We do this based on shared narratives, some of which are religious.   

@Danny705 But since paganism and polytheist religions are so prevalent and predate monotheism and Christianity in particular, wouldn't that mean mankind was evolving towards accepting multiple gods instead of one almighty god? The Epic of Gilgamesh is dated back to 2100 BC, and that's just the first one that got written down. India still practices Hindu, Japan has it's Shinto, until the communist revolution Chine believed in the Celestial Bureaucracy. While these places have wars and civil unrest and such, nothing of the scale of the Crusades, or worse the 30 Years War.

@criminey359 Hey thanks so much for getting back to me. No, I wouldn't agree, I think (I could be wrong I read this in Steven Pinkers book "enlightenment now" ) the fastest growing religion in the world is humanism. Non belief seems to be the most likely religion of the future.

@Danny705 That's a fair point on humanism, but on an evolutionary time scale I have my doubts that can apply as that is within the past hundred years or less that it has been taking off. To see something as an evolutionary trend we would need a lot more time and passing generations. So, clearly we need to become immortal and see if homo sapiens version 2 is more or less religion. So meet back in about 50,000 years and compare trends?

@criminey359 I get what you mean, funny enough religion can change very quickly, for example during the French Revolution people completely changed their sociological presuppositions in far less than 100 years, same thing in the Chinese communist revolution.

You should read "Homo Deus" by Yuval Harari. He lays out a mind blowing argument for the next stage in human evolution.

@Danny705 Thank you for the recommendation. I'll need to look for a copy.