If there is any form of contagion that is adaptive, it is the immediate response to the fear of others. If others are fearful, there may be good reason for you to be fearful too.

Darwin wasn't just provocative in saying that we descend from the apes - he didn't go far enough. We are apes in every way, from our long arms and tailless bodies to our habits and temperament.

If one bird foraging in a flock on the ground suddenly takes off, all other birds will take off immediately after, before they even know what's going on. The one who stays behind may be prey.

Frans de Waal Quotes