What is the 'sin of the world?'

In this week's gospel we hear John the Baptism exclaim, upon seeing Jesus approaching, "Here is the lamb of God, who takes away the sin of the world!" Notice that John does not say "sins" of the world, but "sin" of the world. John is not talking about the many individual behaviors in which people may or may not partake. Instead John is talking about something more communal in nature. Something that is held across all humanity. Across all the world. What do you think is the "sin" of the world? What communal behavior do you see causing suffering in the life of the world and of your community today?