How Does Hair Know When to Stop Growing?

The hair on your scalp can get really long, but your leg hair doesn’t sweep the floor. Why not?

Hosted by: Hank Green
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Sources:http://www.webmd.com/skin-problems-an…
https://www.aad.org/dermatology-a-to-…
http://www.loc.gov/rr/scitech/mysteri…
http://physrev.physiology.org/content…
http://www.livestrong.com/article/109…
http://stemcells.nih.gov/info/basics/…
http://physrev.physiology.org/content…
http://news.yale.edu/2011/09/01/yale-…

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