Goosebumps are tiny elevations of the skin that resemble the skin of chickens after their feathers have been plucked. Goosebumps were once helpful to our animal like ancestors, but are not helpful to modern-day humans. Miniature muscles that are attached to each hair follicle cause these bumps. Each muscle contradicts itself, which causes the follicle to sick out. This action also causes the hair to stand up when ones body gets cold. In animals with a thick fur coat, their muscles use this mechanism to increase the surface of hair to provoke greater insulation. While goose bumps are inevitable when cold, thickness of the hair correlates directly with the animal’s level of insulation.

People also tend to experience goose bumps during emotional situations, such as when someone has anxiety, seeing an emotional video or performance, or even just listening to a song that touches their heart. When animals are in defense mode they extend these muscles to make them look igger and more intimidating to their predator.although humans don’t have the fur coat like animals do, they also subconsciously get goosebumps for defense purposes.

The reason for all these responses is the release of adrenaline. Adrenaline does not only cause muscles to contradict one another, but they also provoke many other body reactions . People can feel this when they are angry, happy, mad, etc. In animals, this hormone is released they are faced with a flight-or-fight reaction. Other signs of adrenaline release include racing hearts, sweating, shaking, etc.

 http://www.huffingtonpost.com/2012/03/23/why-we-get-goosebumps_n_1375723.html