The evolutionary/signaling explanation is distinct from the rewards/conditioning explanation, because the former says that people are predisposed to engage in behaviors that were good signaling in the ancestral environment whether or not they are rewarded today.

As a practical matter of evolution, signal-detection has to evolve before signal-generation, or there's no benefit to generating the signal. And evolution likes to reuse existing machinery, e.g. reinforcement.

In practice, human beings also seem to have some sort of "sociometer" or "how other people probably see me", so signaling behavior can be reinforcing even without others' direct interaction.

It's very unparsimonious to assume that specific human signaling behaviors are inborn, given that there are such an incredible number of such behaviors in use. Much easier to assume that signal detection and self-reflection add up to standard reinforcement, as signal-detection and self-reflection are independently useful, while standalone signaling behaviors are not.