A theory of the origin of ethics which states that people have an unwritten social contract with the rest of society so that order can be maintained. Supporters of this theory speculate that, when human beings first gathered into social groups, they had to agree on rules that would foster group survival; rules reduce conflict and chaos. However, there are 2 important problems with this theory.

It does not allow for the common moral basis we all share as human beings.
Boo for Murder, Hoorah for progress!
In this theory, if one isolated social group decides on a certain set of values, then another separate social group will most certainly decide on a disparate set of rules! The resulting conflict of beliefs would have quickly obliterated our race.

The social contract theory also has no explanation for great social heroes. Many seem to go against the social norms of the times ( both Martin Luthers for example ).

"True morality consists not in following the beaten track, but in finding out the true path for ourselves and fearlessly following it."
    -Mohandas Gandhi