What is the difference between "Man" and "Human" in the broad senses of mankind and humanity? I recognize that some object to the term "mankind" because of the gender connotations. I was wondering if, ignoring that objection, there was a difference and also what the Hu in "human" means. Could people still object to the sexism of language because there is a man in human?
The Online Etymology Dictionary:
mid-15c., humain, humaigne, "human," from Old French humain, umain (adj.) "of or belonging to man" (12c.), from Latin humanus "of man, human," also "humane, philanthropic, kind, gentle, polite; learned, refined, civilized." This is in part from PIE _(dh)ghomon_-, literally "earthling, earthly being," as opposed to the gods (see homunculus)*. Compare Hebrew adam "man," from adamah "ground." Cognate with Old Lithuanian zmuo (accusative zmuni) "man, male person."
"a human being," 1530s, from human (adj.). Its Old English equivalent, guma, survives only in disguise in bridegroom.
Old English man, mann "human being, person (male or female); brave man, hero; servant, vassal," from Proto-Germanic *manwaz (cognates: Old Saxon, Swedish, Dutch, Old High German man, German Mann, Old Norse maðr, Danish mand, Gothic manna "man"), from PIE root *man- (1) "man" (cognates: Sanskrit manuh, Avestan manu-, Old Church Slavonic mozi, Russian muzh "man, male").
Plural men (German Männer) shows effects of i-mutation. Sometimes connected to root *men- "to think" (see mind), which would make the ground sense of man "one who has intelligence," but not all linguists accept this. Liberman, for instance, writes, "Most probably man 'human being' is a secularized divine name" from Mannus [Tacitus, "Germania," chap. 2], "believed to be the progenitor of the human race."
So I am as he that seythe, `Come hyddr John, my man.' 
Sense of "adult male" is late (c. 1000); Old English used wer and wif to distinguish the sexes, but wer began to disappear late 13c. and was replaced by man. Universal sense of the word remains in mankind and manslaughter. Similarly, Latin had homo "human being" and vir "adult male human being," but they merged in Vulgar Latin, with homo extended to both senses. A like evolution took place in Slavic languages, and in some of them the word has narrowed to mean "husband." PIE had two stems: *uiHro "freeman" (source of Sanskrit vira-, Lithuanian vyras, Latin vir, Old Irish fer, Gothic wair) and *hner "man," a title more of honor than *uiHro (source of Sanskrit nar-, Armenian ayr, Welsh ner, Greek aner).
MANTRAP, a woman's commodity. [Grose, "Dictionary of the Vulgar Tongue," London, 1785]
Man also was in Old English as an indefinite pronoun, "one, people, they." The chess pieces so called from c. 1400. As an interjection of surprise or emphasis, first recorded c. 1400, but especially popular from early 20c. Man-about-town is from 1734; the Man "the boss" is from 1918. To be man or mouse "be brave or be timid" is from 1540s. Men's Liberation first attested 1970.
At the kinges court, my brother, Ech man for himself. [Chaucer, "Knight's Tale," c. 1386]
From this there does not seem to be any relation between "man" and "human" because one is Germanic and one is Latin. It seems to me that the "man" in human is just a phonetic shift from homunculus. It could also be possible that both words are derived from the respective culture's origin of man. Is there a relationship I am missing or something related to look at?