Huizinga argues that debating is essentially a human expression of our animal play instinct. https://en.wikipedia.org/wiki/Homo_Ludens
This would also be the reason in settings where debate is formalized, e.g. a courtroom, there are elements of pageantry and pantomime. All playful exaggerations, nonetheless serious (because play can be serious business, look at any child absorbed in a game).
Debating as a means to avoid combat then follows quite naturally. It's sublimation of a primal instinct, channeling dangerous antagonistic behaviors into the realm of harmless play.
The etymology of "debate" is "de-beat", i.e what you do to avoid beating each other, so in principle it's closer to negociation than to mutual battering.