I was wondering, why hasn't religion gone away by now? Infact, if you are an evolutionist how did it get started? Why do we need it?
I don't think there's any such person as an 'evolutionist': that's a word invented purely as an antithesis for 'creationist'. In the real world, there are evolutionary biologists, and other scientists and lay people who accept the vast body of evidence that supports the theory of evolution in the same way they accept other scientific theories; calling them all 'evolutionists' is lazy.
Addressing your main question, I'm attracted to Lewis Wolpert's ideas on our need as a species to create beliefs on which to plan and base actions. He proposes that humankind's first technologies were made possible by our ability to construct cause-and-effect beliefs - 'if I chip this piece of rock like this, it will produce a cutting edge'. From this he extrapolates that where no obvious cause could be seen for significant events (lightning, droughts, floods etc) it was expedient to invent them; hence animisms, the supernatural, and the beginnings of religious belief. Probably not the whole story, I agree, but plausible.
Why do we need it? Dawkins declares we don't: for him it is a functionless and malign spin-off from our brain function, like the noise generated by a car engine - we'd be better off without it. I'm more cautious: in my view, religion has been too deeply embedded in culture throughout human history, and too expensive in terms of time, energy and materials, to be functionless. It's had a role in sanctifying and cementing a culture's moral code, uniting people to a common purpose and legitimising the sociopolitical status quo.
The problem is, Dorothy has now looked behind the curtain and found no wizard: religion's supernatural claims are increasingly questioned, and with them go its authority to direct our lives. In some societies demagogic ideologies have been imposed in its place, invariably dressed up in the trappings of religions (infallible charismatic demigod leaders, unquestionable texts etc); they have not looked good so far. Regretfully, I conclude that religion probably isn't going away in a hurry.