An ape has a small brain.
Humans have huge brains.
These are telling pieces of anatomy. Why?
The Expensive Tissue Hypothesis tells of an important tradeoff:
Our brain weighs 5X what you’d expect for a mammal our size. It uses 20% of our daily energy
expenditure, burning calories at 10X the rate of the body as a whole (...it takes a lot of energy to fire nerve cells and pump ions across cell membranes).
But humans don’t burn more calories than is expected of a mammal our size.
We have an energy budget that we must balance, and the brain takes a huge chunk of that balance.
Thus, we have a conundrum, the brain's huge energy expenditure must be offset by something
else.
The gut took the fall.
If you add our gut and our brain together, their summed weight is what you'd predict for a mammal our size.
The energy saved by a smaller gut compensates for that required by a larger brain.
Humans sacrifice gut size and the ability to process plant material for a big brain that facilitates hunting success via intelligence, language, tool- / weapon-making, and
cooperation.
TL;DR
We aren't the biggest, fastest, or strongest animal, but by sacrificing our large plant-processing gut we could fuel an outsized brain with meat - the tradeoff (gut for brain) that catapulted us to the top of the food chain.