Lice apparently come in three varieties: head, body, and pubic. The body louse’s genome was published in 2010 and is the shortest known insect genome. (Does parasitism reduce genome length?) According to Wikipedia:
Pediculus humanus humanus (the body louse) is indistinguishable in appearance from Pediculus humanus capitis (the head louse) but will interbreed only under laboratory conditions. In their natural state, they occupy different habitats and do not usually meet. In particular, body lice have evolved to attach their eggs to clothes, whereas head lice attach their eggs to the base of hairs.
So when did the clothes-infesting body louse decide to stop associating with its hair-clinging cousins?
So, did Neanderthals have clothes? Or did they survive winters in ice age Europe by being really hairy?
Behavioral modernity–such as intentional burials and cave painting–is thought to have emerged around 50,000 years ago. Some people push this date back to 80,000 years ago, possibly just before the Out of Africa event (something that made people smarter and better at making tools may have been necessary for OOA to succeed.)
But perhaps we should consider the invention of clothing alongside other technological breakthroughs that made us modern–after all, I don’t think we hairless apes could have had much success at conquering the planet without clothes.
(On the other hand, other Wikipedia pages give other estimates for the origin of clothing, some even also citing louse studies, so I’m not sure of the 100k YA date, but surely clothes were invented before we went anywhere cold.)
Oddly, though, there appears to have been at least one human group that managed to survive in a cold climate without much in the way of clothes, the Yaghan people of Tierra del Fuego. In fact, the whole reason the region got named Tierra del Fuego (translation: Land of the fire) is because the nearly-naked locals carried fire with them wherever they went to stay warm.
Only 100-1,600 Yaghans remain; their language is an isolate with only one native speaker, and she’s 89 years old.
Unfortunately, searching for “people with no clothes” does not return any useful information about other groups that might have led similar lifestyles.
PS: Pubic lice evolved from gorilla lice 3 million yeas ago. I bet you didn’t want to know that. Someone should look for that introgression event.
Native Americans appear to also carry a strain of head lice that had previously occupied Homo erectus’s hair, suggesting that H.e. and the ancestors of today’s N.A.s once met. Since these lice aren’t found elsewhere, it’s evidence that H. e. might have survived somewhere out there until fairly recently.