Somebody: Really? Are you saying there's *no* variability in selfishness in different societies around the world? Even if we accept the (dubious) notion that psychology is reducible to social relations, it doesn't follow that capitalism produces a homogenized ensemble of social relations.
There are vast differences in the degree of atomism versus social cohesion, individualism versus communalism, and these don't necessarily fall along the lines of capitalist as opposed to pre-capitalist societies. These differences are reflected, for instance, in the vast disparities in rates of violence in crime amongst industrialized nations - differences which do not easily correlate to poverty or wealth disparities, especially once we include industrialized East Asia.