While we lost body hair to improve cooling through sweat,we retained hair on scalp.
It is primarily to protect the brain from overheating and to conserve water.
When our ancestors began walking upright, the top of the head became the part of the body most consistently exposed to intense midday sun.
Scalp hair acts as follicular helmet reflecting solar radiation away from the head.
Though sweating is the effective cooling method, it comes at a high cost which is loss of water !!!
By shielding the scalp from direct sunlight, hair reduces the amount of sweat needed to keep the head cool.
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