Why dont eyebrows get any longer O_O?

Question

for example : ) if you cut off your eyebrows... they would grow back in about 1 month (maybe) but after 2 months.... they dont get twice as long... after another 20 years they would still be the same lengh O_O... why?

Answer 1

There are different kinds of hair that grow on our bodies.  Some hair (eye brows, eye lashes, arms, legs, & genital) is "determinate", meaning the hair grows to a predetermined length and stops.  "Indeterminate" growth of hair occurs only on our heads and is a feature rare in the mammal world.