I mean, one of the more quoted lines in LOTR is a human woman telling the Nazgul Witch King "I am no ... man." The film quote is shorter and more direct but the book still has Eowyn telling the witch kind she isn't a man. So there are men and women but also man is used to describe humans.
I don't know if you're implying that those haven't been used interchangeably for a very long time or not. Regardless, I'll say it's super old. Man refers to any human. Mankind is humanity. We also say man and woman for gender, which is also super old.
Yeah, I hate the word "modern". It's about a 50/50 that it's being used to say "now" or being used in a technical sense, which is referring to something that really isn't modern anymore. I hope everyone has learned their lesson that time moves on past them and not to use "modern" as part of a name for anything. The fact that "post-modern" is often used to describe things that aren't even new anymore makes it even worse.