For from within, out of men's hearts, come evil thoughts, sexual immorality, theft, murder, adultery, greed, malice, deceit, lewdness, envy, slander, arrogance and folly. All these evils come from inside and make a man `unclean.’”
Deep down we humans continue to be beasts at least up to some degree. Many animals seek to survive at all costs, and in many cases, the big boss (stronger animal, etc) gets everything, including the female. We humans have a bigger brain, and all those primal instincts translate into more complex stuff such as "theft", "envy", etc, which are basically tools to bring us "to the top". Of course, many people are also downright psychopaths (murder just for fun, for example).