Recently, some pro-Darwinists have been attacking religious faith because it's not scientific and rational. But it shouldn’t really matter (to someone who believes in evolution) whether humans are rational or not. It’s the outcome (and effect) our faith has that matters, and how this aids our survival as a species. The belief itself is not relevant to scientific debate.
I’m not a religious person (maybe I'm missing that gene), but you don’t have to be religious to see the effect of religion on human cultural evolution.
Where did God come from? In the last 5,000 years, the human mind evolved to cherish abstractions as being as important as our own survival. First, we invented abstract things like writing, the wheel, rule of law, and democracy. These came about because humans started to see abstractions as being more important than self-preservation. We became obsessed with “the principle of the thing” over practical concerns. This can be seen most clearly in religious fanatics who blow themselves up “for the cause” or “for an idea”. That is the raw inclination behind religion and invention and rule of law.
During the time of the Roman empire (2,000 years ago), life was miserable and short for the average person. Many people began to embrace Christianity, not because it's rational, but because the church promised to support everyone as Christ did, especially the downtrodden and outcasts, who were given a level of care by the church they hadn’t known before. Even when the early Christians were tortured and thrown to the lions for their beliefs, they bravely and willingly gave their lives for the idea of "God" and His grace. Eventually, the Roman empire had to convert to Christianity, because they couldn't fight the faithful any longer.
Christianity, then, has a practical effect. True, it can be open to abuse, because any time you start accepting the words of your leaders on faith (without questioning), they can become corrupt, or launch religious wars. That’s why the Protestant reformation was so important, to remind people they have a direct path to God. He can hear your prayers without the need for an intervening church hierarchy (priests, etc). The Protestant revolution led directly to the humanist idea that every man and woman is an important and sacred individual, the foundation of democracy.
So religion has been very important to the development our modern notions of law, morality, and science and evolution. Is there a God? It doesn’t really matter, does it?