Aristotle's doctrine that human beings are political animals is, in part, an empirical thesis, and posits an inclination to enter into cooperative relationships, even apart from the instrumental benefits of doing so. Aristotle's insight is that human cooperation rests on a non-rational propensity to trust even strangers, when conditions are favorable. Turning to broader questions about the role of nature in human development, I situate Aristotle's attitude towards our natural propensities between two extremes: he rejects both the view that we must bow to whatever nature dictates, and also the view that nature is generally or always to be suppressed or overcome. This middle position requires that Aristotle hold nature and goodness apart, so that the latter can serve as a standard for evaluating the former. He holds that nature does not treat all human beings alike: just as some are handicapped in their development by a deficiency in their natural abilities or propensities, others are extraordinarily fortunate and have so powerful a disposition to act well that they easily acquire good habits and skills of practical reasoning. Further, he recognizes that sociable inclinations and natural virtues have to compete in the human soul with other natural forces that make ethical life extraordinarily difficult. That is why things so often go so badly for us: we need not only to subdue the external environment, but to overcome certain inner natural obstacles as well. Even so, for Aristotle ethical life is not generally alienated from nature, as it is for other philosophers.