Human hair growth
The three stages of hair growth are the anagen, catagen, and telogen phases. Each strand of hair on the human body is at its own stage of development. Once the cycle is complete, it restarts and a new strand of hair begins to form. The rate or speed of hair growth is about 1.25 centimetres or 0.5 inches per month, or about 15 centimetres or 6 inches per year.
Red hair
In Ireland, the percentage of population with red hair is estimated to be at around 10%, making it the world's highest concentrated population of red heads. According to IrelandsDNA, 34.7% of the Irish population carry the allele for red hair, although this doesn't directly translate proportionally into births of red-haired children.