Materialists will maintain that we can derive morality from scientific facts and reason.
In response to this claim, one need only ask them one simple question - what is their scientific reason to go on living? If they are true to their beliefs about human motives, they will explain how the motive to go on living is hardwired into us by our genes - our "selfish genes".
In other words, where morality is concerned, the materialist wants to claim that they are superior to religious folks due to their values being informed by reason and science and not superstition and belief. But when confronted with their own motives to go on living at all, these the materialist attributes to natural selection of genetic mutations - ie, to something that is, well, predetermined, hardwired - in short, irrational