Rousseau starts with his idea of pre-society man. He envisions a happy savage, roaming about the forests, satisfied with the world he finds himself in. This man goes his own way, occasionally happening upon a savage woman and making new savages. Our man lives at the range of the moment, without any future cares. Rousseau goes so far as to say that 'the man who meditates is a depraved animal'.
Frankly, his thoughts on primitive man are so wrong that it's hard to take him seriously. We have every reason to believe that man has been a 'social animal' for all of his history. That men and women have always lived in clans and tribes, whenever possible. The lone hermit is an extreme outlier in human history.
Which isn't to say that he doesn't have some interesting thoughts. Here he speaks of 'pity':
It is therefore certain that pity is a natural sentiment, which, by moderating in every individual the activity of self-love, contributes to the mutual preservation of the whole species. It is this pity which hurries us without reflection to the assistance of those we see in distress; it is this pity which, in a state of nature, stands for laws, for manners, for viture, with this advantage, that no one is tempted to disobey her sweet and gentle voice: . . .The urge to help those in distress does run deep. Rousseau sees it in conflict with self love and suggests that pity wins out. This idea of helping others then, becomes the basis for custom and law. Rousseau goes on to say that pity keeps a strong man from stealing from children or the old. He will work to provide for himself first before depriving them of their hard fought gains.
Rousseau sets this in opposition with Hobbes idea that all men are at conflict with each other. Of the two, I think that Hobbes gets the better of the argument but Rousseau does make me pause. There are some pretty powerful customs protecting children and the elderly though. It takes some very powerful motivation like starvation before someone will take from them.
I wonder what Rousseau would think, if he had a few more centuries of accumulated knowledge behind him?