That was found by a reader who emails:
Greetings Ms. Althouse: Long time reader, so I'm aware of your distaste for men in shorts. One of my retirement activities has been reading every issue of LIFE magazine from its start in 1936. I'm up to 1953 and came across an article that may document the genesis of the short pants for men phenomenon. Lots of pictures I know you'll love (loathe).There's always an exception if the weather is hot enough, at least 80°, and outside of the air conditioning. I'm up here in Wisconsin, where guys break out the shorts when it's in the 40s!
By the way, I live in South Carolina and regardless of how ridiculous I may appear, summers here dictate comfort as a priority over fashion sense.