Humans cluster in social groups where they discuss their shared past, problems, and potential solutions; they learn collectively when they repeat activities; they establish social norms; they synchronize when they sing or dance together; and they bond through social cohesion. A group is more cohesive if its members are closer together in their network and are bonded by multiple connections. Network proximity and redundancy are indicated by the second smallest eigenvalue of the Laplacian matrix of the group network, called the algebraic connectivity. This eigenvalue is key to explaining and predicting the outcomes of said activities.