When fears of contagious diseases such as avian flu and ebola arise, public health officials encourage people to replace greetings involving close contact (handshakes, hugs) with an elbow bump. this change in greetings represents a shift in?

Social norms.
Norms are like informal guidelines that are understood as important to act and behave on a specific society with its cultural beliefs. Being part of a society or culture establishes certain beliefs that lead us to a certain behaviour as social norms. In this specific case, living in an emergent potential risk of a contagious disease, created such norms.

It is evolution, because we all have some of the same traits like eye color or shape or ears.

A. mitochondrion b. nucleus