Utilitarianism

In Utilitarianism, Mill speaks of two levels of pleasure: the physical and the mental. Now there is a hierarchy with these pleasure, with physical pleasures being inferior to mental pleasures. This argument is valid, but it is only through the creation of society that an individual is able to seek these mental pleasures rather then simply seeking the physical ones which the human race is dependent. The question i would pose to this theory, is if pleasures, being mental or physical, is really the goal of the human race? What makes pleasure the goal?