English evolved in a time period, predominatly ruled over by men. Hence, the default term is: "Mankind", "Man", and the default, when gender is uncertain, is to use "Man", "Him", or derivatives of such.

In Old English, the word "man" was gender-neutral, while the words for male and female were something like wer and wif. The compound word wifman, meaning "female human" is what evolved into the modern word "woman" (interestingly, the word wer survives most commonly in "werewolf", which as you can see literally means man-wolf, and distinctly male). Cognates of "man", such as the German Mensch in fact remain gender neutral.

The gender-neutral third-person singular pronoun is "they", with documented use at least as far back as Chaucer and Shakespeare.