I've always felt it was pretty self-evident that the purpose of sapience in mammals is social first. In order to understand social standing and dynamics, a theory of mind is necessary. And, this theory of mind primarily benefits social situations, such as raising children and living in packs / herds / tribes / etc. I also believe this is why you sort of "observe" yourself; your observation of yourself almost happens in the 3rd person, and even when alone you think of yourself as observable.
