I am in no way an expert on the English language, but I have an observation that there is a transition in English into gender-neutrality in the use of adjectives. But still there is no consensus in the English-speaking world about the standardized form.
In the historical English when you say men, you mean all the people in the world including men, women and even gays... and when you say mankind, you mean humankind or humanity...
and for about 3-4 decades there has been a trend to avoid using his or her, but using their is the pronoun of preference even if you indicate a singular person.
now quiz, who is the name of the feminist person who claimed that the word " history " is actually the phrase "his story", to prove that the society is actually patriarchal? Because even the history of mankind is the history of man! can you believe that, it's his story, bro!? :)))))