That's precisely why we have the scientific method, so we don't have to "believe". And based on it, evolution (natural selection) and the big bang (cosmic inflation) are the best answers we have right now.
Also based on it, because we don't "believe" in evolution and the big bang, we keep applying the scientific method and questioning them, trying to find refinements to them and maybe whole new paradigms that completely supercede them.
What's quite clear though is that there's no magic man in the sky throwing bolts and distributing rewards to individuals based on how closely they believe the apocryphal writings of whatever middle eastern medieval crook.