system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What is the biological reason that we are able to grow long strands on our head?
gpt
The strands of hair from our scalps/heads grow longer because the hair follicles there have a much slow "turnover rate" programmed into them than the hair follicles in, for example, our arms. In other words, your arm hairs fall out much more frequently, so they don't have the chance to grow as long.