> No, don't tell him that - I'd like to see how he thinks a species can
> evolve against an external threat within one generation and without
> exposing more than a significant minority of its population to that threat.
You are mis-understanding Darwinism. The premise behind Darwinism is that...
* random shit happens during the reproductive process, resulting in random mutations within a species (e.g. Homo Sapiens)
* random shit happens when the environment throws different survival problems at the species (e.g. AIDS)
* the individuals with beneficial differences (i.e. stronger immune systems against AIDS) are more likely to survive, and procreate, passing their AIDS-resistance mutation to their children
This, in a nutshell is "survival of the fittest". The problem quantifying "fittest" is that it depends on the external environment. E.g. Sickle Cell anemia gene carriers (usually African origin) have higher resistance to malaria, which is a net survival plus in African jungles, notwithstanding some anemia. In the African jungles that meant they survived better, and had more children.
Then some were taken as slaves to the US. 200+ years later, the superior malaria-resistance is not helpful, but the anemia side-effects remain, so it's a net minus.