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.
Projections of population growth
The world population is currently growing by approximately 83 million people each year. Growth rates are slowing to various extents within different populations with result of the overall population growth rate decreasing from 1.55% per year in 1995 to 1.25% in 2005, 1.18% in 2015 and 1.10% in 2017. The median estimate for future growth sees the world population reaching 8.6 billion in 2030, 9.8 billion in 2050 and 11.2 billion by 2100 assuming a continuing decrease in average fertility rate from 2.5 births per woman in 2010–2015 to 2.2 in 2045–2050 and to 2.0 in 2095–2100, according to the medium-variant projection. With longevity trending towards uniform and stable values worldwide, the main driver of future population growth is the evolution of the fertility rate.