Why aren’t humans covered in hair like other primates are? (continued)
Anthony Woodward
Portland, Oregon, US
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David Muir’s hypothesis that being almost completely hairless enabled hominins to chase down prey animals on the savannah without overheating is inconsistent with the data.
The fastest mammal on the savannah is the cheetah, which can run up to 110 kilometres per hour despite its thick coat of hair. Cheetahs evolved about 8.5 million years ago, before the human lineage split from that of the chimpanzee, about 7 million years ago. Two other mammals strut almost naked across the savannah: the elephant and the rhinoceros. Neither species races across the grassland.
Hair doesn’t tend to fossilise, so the exact date when hominins became hairless is uncertain, but evidence suggests that the first hominin to do so was probably Homo erectus, which lived from 1.9 million years ago to around 100,000 years ago. Excavations at Kanjera South in Kenya indicate that hominins were living on the grasslands there 2 million years ago. They were presumably covered with hair and certainly using stone tools consistent with hunting activities.
Trevor Campbell suggests we don’t need hair because we can obtain clothes from furry animals. Our ancestors’ head evolved into clothing lice between 170,000 and 83,000 years ago, suggesting that is when they started wearing clothes, long after they started living naked on the savannah.
Gareth Morgan
Corfu, Greece
There is a vast amount of fossil evidence in shell middens (refuse heaps), some dating back half a million years, that our early ancestors ate a great many clams. This is unsurprising, as clams are probably the most easily acquired source of animal protein that can be harvested in large quantities.
One major drawback of relying on clams for sustenance, though, is that you would probably spend a great deal of time on the mud flats around estuaries. If you were a furry hominid, you would be almost certain to succumb to the often-fatal blood infection called leptospirosis, commonly known as mud fever or Weil’s disease.
Without fur, mud on the skin would quickly dry and flake off. A naked, rapidly drying skin thus offers excellent protection against Leptospira bacteria, which need moisture, and would therefore be favoured by natural selection.
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