Answer:reciprocity
Explanation: Reciprocity is a norm amongst people which is due to the act of kindness committed by one person to us ,that result to us feeling encouraged and motivated to commit the act of kindness back to those people , it is a norm of sharing out of the kindness of our heart because people have also been kind to us.
B. horses evolved to have hooves
C. genetic mutations are the genetics behind adaptations
D. selection is the basis for evolution
E. I'm not sure about the willful part but hooves would be considered an adaptation to the environment <span />
