The materialist (who does not believe in God) is starting out with something akin to faith that everything got here by pure material causes; this belief in matter could almost be called a religion, it is so strong, and by its nature denies any other agency. Here follows a quote from a professor of Zoology at Harvard; note the bias which materialism suffers from:
Dr. Richard Lewontin, the Alexander Agassiz Professor of Zoology at Harvard University, put it like this:
“It is not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but, on the contrary, that we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counterintuitive, no matter how mystifying to the uninitiated. Moreover, that materialism is absolute, for we cannot allow a Divine Foot in the door”
Reference: Richard Lewontin, “Billions and Billions of Demons,” New York Review of Books, January 9, 1997, p. 28.