I've been asked to explain the use of best in the phrase "humans have found how best to live together" other than saying its an adverb I'm stumped, could someone wiser help me out.
Change the affirmative phrase to make a simple question.
How well do humans live together? (correct)
good do humans live together? (incorrect)
In your sentence:
Humans have found how best to live together"
"how best" = best is the superlative form of the adverb, well.