When it comes to apologetics, the question, “By what standard?” really is a fundamental question. The same question arises in disputes on many playgrounds—it's the same thing as asking, “Who says?” If you claim that I have to do something, the question should come back, "Why do I have to do this?" It is at this point that a presuppositional approach to apologetics has its cleanest shot. A good place to go to study this approach further would be something like Greg Bahnsen’s Always Ready.
During our three days together making Collision, this was one of the few times where Christopher was brought up short. I think it was because the question here was a complete novelty for him, and he needed a moment to think about it.
When he tries to answer the “By what standard?” question, notice how he smuggles in the assumption that I am asking him to prove. He says that he knows certain (moral) realities because he is among the “higher primates.” But there is a word in there that is value-laden—higher. Higher by what standard? What are we talking about?
Christopher set up the next exchange nicely by acknowledging that as primates, we have a jumble of conflicting instincts. The response I offered was something I first learned from C.S. Lewis. If I have two competing and contradictory instincts, an evolutionary approach can account for each of those instincts (say, self-preservation and herd preservation). What it cannot account for is a third instinct that tells me which of the first two instincts I ought to obey in this instance. I do not have an “umpire” instinct that decides between them.
What I do have is a conscience, which cannot be accounted for apart from God. Christopher tries to take a “conscience vote” among the students there when he brings up the question of eternal torment. But we don’t need a conscience vote. We need to account for why we have consciences in the first place.