Hobbes and Rousseau

My question when reading Rousseau, is to what extent is our behavior in a society natural?

Rousseau claims that pity is a natural attribute of most animals, including humans, and that this pity is stripped and replaced by greed when we enter into a society.  This goes in direct opposition to Hobbes who states that pity is learned and greed in natural.  My concern with Rousseau's assumption is that it doesn't account for the natural way in which humans interpret their surroundings.  In my line of thought, an institution created by people is inherently subsequent to people, and cannot be considered wholly separate from its creator.  Therefore it must in someway represent the natural disposition of mankind, as its foundations are rooted in our basic needs and desires.  Furthermore, the reaction an individual has in regards to society is a natural reaction, and cannot be determined as completely controlled by the society.  For example, when we are presented with an advertisement, our reaction will always be the natural state of reaction that our mind allows for.  We are not subject to the advertisement, but subject to the natural course of interpretation.  It may be argued that this interpretation is the product of society's influence; however, whatever initial reaction we have to a society cannot be subject to it, as it has not left any mark on our mind at that point; and we have all had this initial interpretation.

It then seems that acting greedy when placed into a society is not an effect of the society on the individual's mind, but the natural mode of behavior of the individual when placed into a society.