Why is the sympathetic division of the ans called the "fight or flight" system?

The fight or flight system is a reaction that the body undergoes when put in an either stressful or frightening situation. It includes both the nervous and endocrine system. 

The sympathetic division of the peripheral nervous system is used in this response as the sympathetic nervous system works up the body, increases the rate of breathing, heart rate, dilates the pupils, produce more sweat and slow the digestion rate. This reaction happens in the flight or fight system. 

North carolina ranks second in christmas tree production has nothing to do with biotechnology

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