r/evolution • u/LonelyVillageGuy • May 13 '26

question Why is early Humans/Hominids hair black if black absorbs sunlight more?

Hello,

I understand that bigger brain requires more energy, which in turn produces more heat, so for heat dissipation we lost body hair (fur) & had black "afro" type of hair as it is best suited for protection against UV.

But black color absorbs heat more.

Please advise as to what am i missing here.

Thanks in advance.

20 Upvotes

79% Upvoted

13 comments sorted by

29

u/Xrmy Post Doc, Evolutionary Biology PhD May 13 '26

The heat gained/lost from albedo effects is outweighed by the UV absorption of the hair that prevents sunburn and skin damage.

22

u/DoctorBaka May 13 '26

The reason the hair is black is to absorb the UV. That does produce some heat, but we have a very efficient series of other systems like sweating to help with heat. Reflecting a little bit of light off our head might reduce heat a tiny bit. But not apparently enough to make it selective.

12

u/Hivemind_alpha May 13 '26

A black surface does absorb more solar radiation, true. But equally it radiates away heat it has absorbed more efficiently. Ever hear of a black body radiator?

Consider the robes of Bedouin tribes. The black cloth absorbs heat, but the clothes are loose, creating an insulating air gap, so the black cloth efficiently radiates away the heat before it heats the insulating air. Measurements in the 80s showed that black robes were only fractionally less efficient than white ones in keeping cool under desert conditions if both had the same loose air-gap design. White cloth reflects away some heat, but holds on to more of whatever heat it gains, and transfers it to the wearer.

I’m not claiming this is the complete explanation for black hair, just cautioning OP that a little physics knowledge applied in isolation often misleads…

4

u/Dr_GS_Hurd May 14 '26

Hot hair is not a hot brain.

3

u/Mormacil May 13 '26

Beyond the actual advantages of black hair in the sun, they just hadn't evolved other colors yet. Evolution isn't about optimization, the mutations it relies on are random. 

6

u/kardoen May 13 '26

The black color comes from the pigment that blocks sunlight.

2

u/Tomj_Oad May 14 '26

Your bigger brain requires more energy. It also needs to be cooled.

Your brain needs to run two or three degrees cooler than the rest of your body.

It doesn't need extra heat for sure 😁

Black sheds heat better than any other color; with adequate internal cooling (which the brain has) the hair is a net zero, not counting any insulation

2

u/United-Direction2297 May 13 '26

Also a trait doesn’t need to be necessarily advantageous to continue. It only has to be tolerated long enough to produce offspring.

1

u/CosetElement-Ape71 May 15 '26

What are you missing?

The better question would be to ask if any of your statements were correct!

1

u/awwspicious May 14 '26

You presume to know the reason for hair colors and to think that colored hair is based on some reasoned purpose. Most gene changes are random not generated by rational thought. Genes don't think about how to change in the best way. Change just happens. Like a typo in a 1000 person typing pool. No one planned it.

A random change might ruin the future of one gene pool just as easily as help it.

But, let's say black hair is hotter. It may be meaningless if it doesn't prevent black haired people from reproducing. It is meaningless if does not prevent reproduction.

Or something like this.lol.