[vibrunazo]

If I were to guess, it's just a consequence of arrogance. Which in itself is an evolutionary artifact that was necessary for our survival. Imagine if we were 100% humble about every subject. Then you'd be 100% agnostic about every problem, and then never make any decision.

"Should I hunt a deer? I don't know, I don't think I'll ever know." Then dies of starvation. At some point you need that little drop of arrogance to tell you. "That's it, I'm right, I need to do this." Even tho, technically, you can't be sure.

So a little bit of arrogance is necessary for animals to function. We evolved into beings with a drop of arrogance because the ones without this trait died off. Natural selection made sure both extremely humble and extremely arrogant personalities were evolved away from.

And bragging about is just one of the many consequences of arrogance. We're arrogant + we can communicate = we brag.