Expert: Florence M Rollwagen - 11/17/2008

Question
Hello,

I was thinking recently about how hair relates to evolution.

Would you know why black people have curly afros and other people have straight hair?

Thank you,

J

Answer
Hi John:  Thanks for your question.

Many scientists believe that humans lost their body fur as a result of increased hunting during the day.  This enabled the development of sweat glands to cool the body during the intense heat of the tropics.  Maintaining tight curly hair on the head protected the body (remember we were upright at this time) from the sun.  It is believed that the tight curls prevented uv radiation from penetrating to the skin.  At the same time, humans were developing dark skin which also protected the body from uv radiation, so loss of fur would not be harmful.

As humans migrated out of the intense sun of the tropics, they no longer needed protection.  As you probably know, the skin makes essential vitamin D after sun exposure.  As humans moved to areas where the sun was weaker, dark skin may have been harmful in that the people with darker skin made less vitamin D, and had poor bone development.  Those humans with lighter skin made sufficient vitamin D to allow for walking, running and child bearing.

Again, tightly curled hair would have prevented sunlight reaching the skin, especially as people wore more clothes in colder climates, so the need for vitamin D was greater.  Straight hair does not block the sun as efficiently.

You can get more information here:

http://en.wikipedia.org/wiki/Hair

Hope this helps.  Write back if you have more questions.

FM Rollwagen, PhD