I am always told prostitution is the oldest profession, but am never given any evidence. It makes more sense to me that hunting or gathering alongside a barter system is more likely. Can anyone provide evidence to back up what really is the world's oldest profession?

I don't think hunting and gathering were really professions anymore than you cooking food in your house is a profession. That's just how people got food on their bellies. It's probably a better question for r/askanthropology , since prostitution predates history. I think the phrase is meant to be more tongue in cheek than fact though.