OOA (with minor admixture) is the consensus position for a lot of excellent reasons.

There's a different way to think about this that is closer to how evolution actually works and will make the answer clear.

Our common ancestor (common to orangutans and humans) did evolve intelligence (concurrently with harnessing fire, clothing etc.). Not all of them, but some of them. And they broke off from the group. We now call them humans.

All of the great apes are incredibly intelligent in comparison to most other animals. The basic roots of our intelligence are probably a common feature to the whole family, but there's no consensus on why it's so advanced in humans. Any paleoanthropologist can rattle off about half a dozen possible explanations, but we honestly don't have enough evidence to really distinguish if, when, and how these were factors at different points in human evolution. Here's a quick attempt at some broad categories, which each have multiple hypotheses within them:

* Because intelligence had advantages for individual selection (e.g. mimetic recall hypothesis)

* Because intelligence had advantages for group selection

* Because intelligence had advantages for sexual selection (spandrel hypotheses often start here)

* Because adapting to rapidly varying ecological conditions required so many adaptations that we crossed some kind of barrier and "fell into" intelligence

* Because intelligence helped with foraging/hunting (exclusive of sociality)

It's actually quite difficult to define human intelligence. Every time we think we find something unique by humans eventually some animal turns up that can do it too. It may be all just a question of degree and how it's used.

What would "intelligence" look like WHILE it was evolving?

A slightly more unsettling thought: How would newly-emerging intelligence FEEL like, internally?

Also, how would humans fare if born and raised in the wild, without any language or tools taught to them?