Scientists don’t definitively know the reason behind this change from thicker, coarser fur to these light vellus hairs, and they also don’t know exactly when it happened. Still, several theories have been suggested as to what could have sparked the loss of our hair.
The most dominant view among scientists is the so-called “body-cooling” hypothesis, also known as the “savannah” hypothesis. This points to a rising need for early humans to thermoregulate their bodies as a driver for fur loss.
During the Pleistocene, Homo erectus and later hominins started persistence hunting on the open savannah – pursuing their prey for many hours in order to drive it to exhaustion without the need for sophisticated hunting tools, which appear later in the fossil record.
This endurance exercise could have put them at risk of overheating – ergo the fur loss, which would have allowed them to sweat more efficiently and cool down faster without needing breaks.
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Evidence for this theory also comes from studies that have found switches for some genes responsible for determining whether certain cells develop into sweat glands or hair follicles.
