nighttime temperatures in the lowland nonseasonal rainforests worldwide seem to range from 22-26 degrees celsius, probably closer 22 degrees celsius.
according to johan forsberg of nordic busgcraft, "28 degrees Celsius is the temperature where the human body can lay down naked and rest without being cold or sweating. If it is colder than that or there are cooling winds that we need clothes on our body." http://www.mikaelstrandberg.com/2013/01/04/paradise-or-hell-life-be...
this seems spot on. this is the reason i love the rare 30 degree or so summer days we get here in southern ontario. it allows the house to warm up enough so that it's around 27-29 degrees celsius at night even though the temperature outside would probably have dropped down to the high teens. this indoor temperature of 27-29 degrees makes for ideal conditions for sleeping naked.
having attempted to sleep naked outside in a hammock in a lowland nonseasonal climate zone however, where it was around 22-24 degrees celsius at night, i can attest that naked at rest at this nighttime temperature is somewhat chilly. I definitely wanted a light sheet to cover up with.
my question is this. assuming tony wright's theory that naked homo sapiens arose in the rainforest and not on the savannah like orthodox anthropology dictates, prior to fire and clothing and even shelter how did naked rainforest humans deal with the supposed slight thermal stress they would have been under when the temperature dropped to 22 degrees celsius at night? did they huddle together? did they cover up with large leaves?
i will say that i certainly believe it's possible to sleep naked at 22 degrees celsius. the thermal stress you'd be under would be relatively slight and likely not that big a deal. importantly too, you hypothetically wouldn't even feel the chill if you fell asleep when the temperature was still closer to 30 degrees celsius, which it remains at for a significant length of time after sunset in the rainforest.
what about shivering? this reaction certainly evolved in the rainforest. but it seems odd to most of us that someone would shiver at 22 degrees celsius. but that is because most of us don't have a good idea of what naked feels like at this temperature, since we're always wearing clothing. also being in direct sunlight at this temperature would make it feel signicantly warmer. but naked under the shade of the canopy or after sunset at 22 degrees celsius with rain coming down and wind blowing or even a slight breeze, and you would definitely start to get the chills bordering on shivering, not violent shivering, but some kind of mild shivering would set in under these conditions.
given the temperature at which a naked human at rest begins to feel thermal stress, it's clear that humans have zero tolerance of the cold. we are probably the least cold-hardy animal on the planet. when it comes to the cold, we certainly are delicate naked tropical apes.