Well how else would we have run down our food?

What I've read mostly is that humans, when running, can breathe independently of their stride

That is, we don't have to breathe in on one part of the stride, and out on the other

If you watch, horses, greyhounds, gazelles, or cheetahs, you can see when they're breathing in & out, because of the way their bodies stretch & contract as they run

Ours don't do that [because we're vertical?]

Once that was achieved, other adaptations came into play, like better hearts & lungs, and [with better richer proteins] brains

https://www.npr.org/...diet-made-us-smarter

Then we figured out fire, and things really took off

https://www.npr.org/...y-humans-grew-bigger

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