We were probably much better at running earlier in our evolution. Just as we have become taller in the last 100 years, we also over time have probably lost some of our physical qualities that made us good runners/hunters.
"...and then doing it for years on end."
We live on average at least 4 times longer than our prehistoric ancestors. They didn't deal with long term wear and tear like we do.
Yup, did at least 30 miles a week for 40 years before I started to "climb the ladder of age" and had a few problems.
Now it's walking 30 miles a week. Very boring compared to running, so I took up golf (and walk, no cart!). Still miss running.
Certainly for me it works and it's also a good time for me to come up with ideas. Unlike other exercise my mind seems to go blank when running/walking and a solution to a problem will just "pop" into my mind, without thinking about it.
And I think God made our bodies for physical work. We can change our environment to eliminate it, but we're still wired that way. Good for the body and the soul.