[Paul Morgan]

Paul Morgan  asked the Naked Scientists:
   
Chris and the crew.

Is it possible to explain why human skin colour appears to be the wrong way around?

By this what i mean is we know that a dark colour absorbs heat while a light colour reflects heat, so why are humans born near the equator generally of a darker skin tone.  When surely they need to reflect heat to help them stay cooler, while humans further away from the equator, where it's colder, appear to have lighter skin tones which reflects the small amount of heat generated by the sun in the dark winters. Is there a sensible reason for this or has evolution made an error.

Many thanks

Paul

North Lincolnshire
What do you think?

[CZARCAR]

black absorbs & RADIATES heat better, stay in the shade= Kirchoff's law. Note that white skin also darkens thru tanning

[Bored chemist]

It's not an issue of keeping cool.
The black pigment in the skin absorbs UV light that would otherwise cause a lot of damage.
Further from the equator there's less need for UV protection and a greater need for some UV to get through to make vitamin D
http://en.wikipedia.org/wiki/Vitamin_D#Production_in_the_skin

Re. " Is there a sensible reason for this or has evolution made an error."
please see the second rule here.
http://en.wikipedia.org/wiki/Orgel's_rule

[Phil1907]

It is not a "reason" - sensible or otherwise- no superior being reasoned and established dark pigmentation as better in climates of greater exposure to radiation.  Evolution is not reasoned process and it doesn't make "mistakes"  - it is shotgun and emperical.
It happens that dark skin is more common in some of those environments and melanin pigmentation of that darker skin does provide active and passive protection vs. radiation of all types.

[CliffordK]

Oddly, Melanoma is also much less frequent in darker skinned individuals than in lighter skinned individuals.  Perhaps part of the reason is that the number of malanocytes are about equal in all humans, just the melanin producing activity of the melanocytes varies.  So, in the darker skinned individuals, the melanocytes are better protected.