You ever see the difference between the male Orangutans of Sumatra vs. Borneo? Where food is abundant and the males do not fight, makes tend not to develop the massive face. Where food is scarce and males live solidarity and in competition, they tend to all develop the large leathery cheeks. Scientists claim not to know how it works, but I'm sure it is related to what we see here. Stressing a male body must cause a feedback loop of hormones that strengthens it, even to the point of physical transformation.