Evolutionary biologists suggest that the genus Homo arose in East Africa approximately 2.5 million years ago (Jablonski, 2006). They devised new hunting techniques. (Jablonski, 2006). The higher protein diet led to the evolution of larger body and brain sizes (Jablonski, 2006). Jablonski (2006) postulates that increasing body size, in conjunction with intensified hunting during the day at the equator, gave rise to a greater need to rapidly expel heat. As a result, humans developed the ability to sweat and thus lost body hair to facilitate this process (Jablonski, 2006). Some note that other primates and horses have armpits that sweat like those of humans and so this was not a new evolution, rather a possible preferential selection of perspiration over body hair. However, it can be argued that these two species also pant; a device that compensates for inefficiencies in the evaporation of sweat due to fur. Some counter the argument that dark skin was necessary following loss of fur by suggesting that tanning on exposed skin in primates is also seen and possibly was a retained feature, while hyper-pigmentation as in Africans and Indians, as well as albinism are later mutations. However, this argument doesn't account for the fact that equatorial UV light is such that the relatively minor tanning that occurs among chimpanzees (who, it should be mentioned, spend most of their time protected from the sun by way of a forest canopy), is insufficient in terms of providing full protection.

In addition, while some individuals affirm the hypothesis concerning loss of hair via the evolution of sweat glands, they assert that the question remains as to why such a large surface area is required for cooling when other animals in these regions have much larger volumes to surface area, yet are still covered in thick fur and are able to cool solely by panting. They cite examples that include monkeys, lions and zebra, (though as previously mentioned, they acknowledge that both zebra and monkeys possess the ability to sweat). However, this assessment fails to account for the fact that the speed at which the human lineage changed in response to higher cognitive ability far outpaced that of other species. Specifically, the fairly sudden invention of stone tools by primitive humans ~2.8 million years ago rapidly transitioned the human lineage away from the simple scavenging of protein from the bone marrow derived from the kills of large African predators (a fairly passive endeavor), towards active hunting that entailed spending relatively long periods of time chasing wild game in the hot equatorial sun. Such a pace of change was unparalleled among other species who, instead, acquired their adaptations to the African heat over considerably longer periods of time during which many of them moved into the equatorial region at a gradual pace. Thus, the significantly greater urgency amongst the members of the human lineage for heat adaptations that could keep up with the huge nutritional benefits that they were accruing from the practice of hunting (leading to an avalanche effect in which increasing protein intake fueled increasing brain size/intelligence) may explain these stark differences.