Human evolution: hairless (Introduction)

by David Turell , Friday, July 31, 2020, 23:16 (1362 days ago) @ David Turell

We are the only advanced mammals with little hair and sweat glands:

https://www.sciencedirect.com/science/article/pii/S0047248416000300?dgcid=raven_sd_reco...

"On balance, then, a combination of energy savings with thermal benefits and locomotor advantages would seem to provide the most likely selection pressures favouring bipedalism in the australopiths, with the locomotor advantages probably becoming increasingly important with Homo in order to facilitate a more nomadic ranging pattern and the occupation of lower altitude habitats under significantly cooler thermal regimes.

"Our results suggest that, while hair loss would have provided australopiths with substantial thermal advantages in more open habitats, the night time costs of reduced fur cover were very considerable and thus likely to militate against it so long as the australopiths occupied moderately high altitude habitats. Hairlessness would seem to have necessitated strategies to counteract overnight cooling and/or the occupation of lower altitude habitats. Heat loss at night can be reduced by the use of caves (which can raise mean ambient temperatures by as much as 4 °C

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"Although caves probably have been used as night time refuges intermittently throughout hominin evolution, the use of caves may not have become a regular feature until hominins developed home bases, and that may have coincided with control over fire and the acquisition of a more human-like life history around 500 ka,

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"A more plausible suggestion is that hair loss appeared with the arrival of Homo around 2.0 Ma, once the climate cooling that set in after 2.5 Ma allowed hominins to occupy somewhat lower altitude habitats. It is doubtful that australopiths were sufficiently mobile to make hair loss advantageous, but the appearance of a genus with a body shape better adapted to long distance travel (Homo ergaster locomotion was ∼50% more efficient energetically than that of early australopiths), combined with the first uncontroversial evidence for the occupation of lower altitude (including coastal) habitats (as evidenced by the fact that H. ergaster was able to migrate out of Africa into Eurasia quite soon after its first appearance), might signal the appearance of a suite of adaptations enabling greater mobility in more open, hotter habitats. Hair loss may thus be a peculiarity of our genus, and may have played a small but important role in allowing Homo to escape the confines of Africa."

Comment: Hair loss is certainly peculiar to our species. Sweating which also appeared with loss of hair is also an attribute which helps us during high energy exercise activities. What is odd is horses sweat, even while very hairy.