HAIR KNOWS WHEN ENOUGH IS ENOUGH!
Hair is a thing with frameworks and clockworks that make up a phenomena. What kind of phenomena? Well, lets take a look at what makes up the system first so we can get a better understanding what makes up the phenomena.
So what is this thing we call a hair? A hair is a fiber composed of protein called keratin. The texture of hair is determined by the shape in the follicle, round follicles produce straight hair, oval follicles produce wavy hair and flat follicles produce curly, kinky hair.
The framework of a hair are that hair grows on humans and other mammals. It grows only from the root which is embedded in a hair follicle. Therefore, a hair does not grow in length from the opposite end or in width along the hair shaft. Hair also has a limited range of natural colors. The shades range from black, reds, brown, and blonde. No color, or white, is often the case as people age. For humans and some animals, hair can change color. Humans see change of hues throughout their life as a natural process, sometimes hair is lightened in response to exposure to sunlight. For many people, hair changes to a white shade as they reach their older years. Stress can cause this process to happen prematurely. Humans and animals that have no pigment, thus have white hair their entire life, are called albinos.
The clockwork of hair would be the cycle of hair growth. Each follicle that produces a hair is on it's own independent cycle of growth and rest. This growth varies from person to person and also depends on the location of the body. The cycle of hair in the eyebrows, for example, is 28 days. Whereas on the scalp it is 1000 days.
The rate of hair growth can vary also depending on the location on the body.
So, now we can talk about the phenomena. We know what hair is, what the conditions are for a hair to grow and the cycle involved in growing hair. What we do not have a grasp on is how the hair knows when to stop growing at a particular lengths. Other than a few exceptions, the length of hair is similar from human to human in corresponding locations on the body.