Far off the subject now, but why not?
Yes is from Old English gése, gíse, etc., probably from West Saxon glese, "an affirmative word confined to English," OED.
An interesting note that the pronunciation 'yis,' now dialect, formerly was used in polite speech.
The OED gives many examples of its use through time, starting with Aelfric, c. 1000.

Aye, ay, appeared suddenly about 1575; origin unknown. At first always written 'i.' OED
1576, in Tyde Taryeth no Man- "If you say I, syr, we will not say no."

Should not be confused with another word with the same spelling- ay, aye; meaning always. (OED)