@Aroundtheworldin80moves
One small step for [person], one giant leap for [personkind]
Its funny how replacing Men or Man doesn't really change the meaning...
Well, in that case, it was using "man" in its now secondary, older (and hence more poetic) meaning of "person". So changing it doesn't change the meaning, just makes it less poetic-via-archaic-language. The capitalisation specifically indicates that - see below.
The use of "man" for specifically male is newer - the Old English word "wer" fell out of use and people just started calling males "men".
Seems like evidence that even back then people found it easy to see that men were people, but women weren't quite. "Human" had to be invented later to fill in the lack of a specific word for "men including women", what with "men" being ambiguous. wif/wifmann stayed and eventually became "woman". The "man" in "woman" has that "person" meaning.
Only obvious place you see "wer" in modern english is "werewolf" - "man wolf".
And the insistence that "man" has the "specifically male" meaning - rather than just being ambiguous - person or male - is very recent. That's second half of the 20th century.
Referring to the capitalised Man:
One interesting convention that was thought up in the early 1900s to deal with this issue of “man” coming to mean both male and female and also sometimes meaning males exclusively is, in literature, to do the following: when referring to humans, “man” should be capitalized as in “Man”; when referring to “man” as in “male”, it is to be left lower case. This convention was used in such literary works as “The Lord of the Rings” and was a key point in the prophecy concerning the Witch-king of Angmar: “no man can kill me”, meaning that according to the prophecy a woman, Eowyn, could because “man” in the prophecy was not capitalized.