Whether you are exposed to a chilling wind, swept up in the passion of a ballad, or suffering a fright, a common phenomenon is that of cutis anserina. This is the medical term for a common physiological occurrence known as goose bumps, which involves the appearance of small bumps all over the skin's surface in response to cold temperatures or strong emotions. Whilst everyone has experienced this at some time or another, not many people stop to think twice about it and wonder why it happens, or what function it is meant to serve.
Why do goose bumps appear?
When you think of how a cat protects itself, the immediate image that comes to mind is of a puffed up snarling animal with hair standing on end. Porcupines exhibit similar behaviour in fear, differing only in the fact that they are covered in spines that protrude from their body and act as an effective defense mechanism. In fact many animals use the same tactics to provoke fear in their opponent and gain an edge in battle.
Goose bumps are also useful to animals during cold weather. Raising thick hair acts to regulate the animal's temperature and protect it from the cold. Humans may not have spines or dense enough hair to benefit from the thermo-regulative effect or use this strategy in a fight, but their ancestors did, and in this sense goose bumps are the remnant of a trait that has gradually became vestigial with evolution.
What causes goose bumps?
Goose bumps are a reaction controlled by the hypothalamus, which is a small organ in the brain stem responsible for controlling the central nervous system. When exposed to cold weather or a threat, the hypothalamus sends signals to the adrenal cortex and initiates a release of hormones from the nearby pituitary gland which travel to the adrenal glands and cause the neurotransmitter epinephrine to be released. This is popularly known as adrenaline and is the main participant in the fight or flight response along with cortisol, and acts to initiate the occurrence of goose bumps.
In response to the epinephrine and fight or flight respnse, signals from the autonomic nervous system provoke tiny muscles present in hair follicles called arrectores pilorum to be stimulated and contract to produce a small raised bump and the hair inside the follicle will become erect. This is called piloerection and is the unseen mechanical force behind the appearance of goose bumps.
The appearance of goose bumps is not likely responsible for any beneficial action according to research, and is an example of many traits and organs which have become vestigial with evolution. Nobody knows exactly what path humans are on in their evolution, but what is known is that vestigial traits offer a fascinating story of our heritage and the mysteries of life.