I think in a survival situation, social standards of beauty would likely fall by the wayside. People would still fall in love, and still have their own personal standards of attractiveness probably, and who knows how breeding would go. They might have to go for the most babies, with the most genetic variety possible, produced in the least amount of time. But the whole focus on physical beauty might just not be important. I've realized that the cultures I know about and am thinking of are all ones that were/are/thought they were safe. Starvation (well, unintentional starvation) at low levels, no worries about invasion (though in at least one case they should have worried), etc.