But if the changes in society invoke changes in behaviour, then that suggests that ther isn't an inherency in the nature of humans.
I can see why you invoke primordial man as an example, but really that's ducking the issues. We can't really make assumptions about that, as we know little of their mindset and what drives them.
I'm also not sure of the self interest and health idea either. People definately panic, and in that situation, then no rational decision is possible. Is that self interest or instinct? Can you make a moral judgement about it? Morality must involve intent.