Where did loyalty come from?

Question

what would psycopathy in stall?

Answer 1

Same place any adaption comes from. The first group of organisms in the population of humans to have even a slight propensity for loyalty, which would have given them a reproductive advantage, would have been selected for and had the genes for loyalty driven to fixity in the population.

Remember, though, there are other strategies that are negatively frequency dependent and are anything but loyal. Psychopathy comes to mind.

Answer 2

Psychopathy, or sociopathy, in its most extreme manifestation is where the individual does not empathise with others, and therefore sees them as tools or as a means to an end. The sociopath is therefore unlikely to assist others, exept where he or she sees a clear advantage for him or herself. Altruism and loyalty are abstract concepts, only understood as useful impulses that other display.

There are studies, like the Prisoners' Dilemma, which explore the likelihood of cooperation between individuals.

You might get more information if you asked this in Social Science - Psychology.