Philosopher Peter Kreeft at Boston College presents a version of the moral argument for the existence of God in this short video titled "Where do Good and Evil Come from?" His arguments are brief but cogent. The overall argument involves a couple of steps:
First, good and evil are objective realities, they're not simply matters of an individual's subjective feelings.
Second, the source of good and evil is either natural or supernatural.
Third, if the source is natural then it's likely to come from either evolution, conscience, human reason, human nature, or a utilitarian ethic.
He argues that none of these can explain moral duties. It therefore follows that moral duties must derive from a non-natural, or supernatural, source, i.e. God.
Watch the video to see how Kreeft develops this and see what you think:
I'd add to his argument that if we posit evolution as the source of moral values then we're saying that since we have evolved a sense that kindness is good it therefore is good, and we thus have a duty to be kind. The problem with this is that a sense that selfishness is good, conquest is good, and power is good have also evolved in the human species. Are we therefore to believe that these things are good and that we thus have a moral duty to be selfish, to conquer, and to seek power?
The only way we can deny that these things, being the product of evolution, are good is if we are holding them up to a higher standard of good in comparison with which they're seen to fall short. But on the assumption that our moral duties are solely the product of evolution there is no higher standard.
The claim that a behavior is good because we have evolved a propensity for it commits what's called the naturalistic fallacy. This fallacy occurs when one concludes from the fact that something is a certain way that therefore it ought to be that way, but philosophers ever since David Hume in the 18th century have pointed out that you simply cannot derive an ought from an is.
