According to Rousseau's Discourse on Inequality, there are four stages to the social evolution in humans; it's natural state, family, nation, and civil society. There are two types of inequalities, natural (or physical) and moral. Natural inequality stems from differences in age, health, or other physical characteristics. Moral inequality is established by convention or consent of men. One of the first and most important questions Rousseau asks is " How can one know inequality without knowing man?" To answer this question, man cannot be considered as he is now, deformed by society, but as he was in nature. The problem is that as knowledge increases our ignorance of the true nature of man decreases. Rousseau's enquiry will not deal with historical truths, but with hypothetical and conditional reasoning. This leads us to the first stage of social evolution: man in it's natural state.
It is important to see man at the beginning. If you strip man of artificial faculties, you see an animal that is less strong and agile than other wild animals, but the most advantageously organized of all. Savage men are toughened by exposure to the elements. Natural man's only tool is his body. Savage man sleeps much and thinks little. Self-preservation is his major care. To succeed in this, he needs strong senses. Both man and animal are essentially mechanical, but man has the ability to act freely, which allows him to choose and vary his behavior. More importantly, humans have the faculty of perfectibility. Men cannot only choose, he can also change rapidly. Without this quality humans would remain in the state of nature forever, and never progress beyond the level of other animals. Savage man has no needs, and his only passions come from nature. Food, sex, and rest are the only good things for him: the only evils are pain and hunger. Rousseau argues that the passions produce reason in man, by producing needs that that require him to think in order to satisfy them.