I listened to Born to Run and really enjoyed it.
And from what I've seen online, and what was said in the book, I'd have to believe Grok might have been a marathon hunter.
The logic behind persistence hunting, and I can attest that running barefoot without heel-striking is quite a bit easier (just so we are very clear, I'm 6'1" and 275lbs, big and tubby), and I'm finding it quite enjoyable.
On top of that I don't see why Grok wouldn't have ran (still waiting on the book...).
Anyways, once the book is in my hands, I'll read Mark's arguments, and write up an article.
Once you learn that you create your own reality and that you are fully responsible for your life, you can begin to see the world as it is and then you realize the limitless possibilities.