I once attended (auditing, as it were; a friend of mine was teaching) a U.S. history class at a community college where a couple of Civil War re-enactors (in uniform) gave a talk on daily life for a soldier of that war. One said that whenever a man got an officer’s commission in either army, the first thing he did was to buy a silk shirt, because silk repels lice (always a trouble in a military camp).
Does silk really repel lice? How does that work? Why would lice be averse to the substance of moths’ cocoons?
Lice like to live on rough surfaces where they can get a grip, so clothing made out of a smooth fabric like silk is less likely to become lousy than clothing made out of a rough fabric like wool.
So, humans have been wearing clothes long enough to shape the species’ evolution. Interesting. But probably not surprising, when you consider the speed of insects’ reproductive cycles, and, thus, how many more generations of lice than of humans have been born since paleolithic times.
Also not surprising when you consider how much of our clothing was (and still is) made out of the hair and/or skins of other animals. The initial jump was probably a trivial one and I doubt that adapting to cotton was much of a stretch for them.