I recently ran a marathon. I trained "primal-style" (sprints and long slow runs) and fueled with fat. I wasn't competitive, but it was my first marathon and I was simply hoping to complete the thing! Which I did! Yay!

Three important things:

1. my friends said that I recovered much faster on the day of than they expected me to.
2. my quads were my only sore muscles after, and only for three days.
3. I never did hit a wall!

I think there's something to your line of questioning... Not sure where we go from here. More research is necessary, I think.

There seems to be reasonalbe evidence that running played a role in our evolution. We are far better at running longer distances than any other ape and far worse at sprinting (just try to outsprint a charging gorrilla, chimpanze or babboon). http://www.nature.com/news/2004/041115/full/news041115-9.html

I like the idea that it played more of a role in scavenging to begin with. A group of hominids sighting vultures circling on the horizon could run the distance and reach a freash kill or death, grab the best bits before the larger hyenas got there. Persistance hunting has most likely always been an option for hunting where conditions are suitable. It is unlikely to work so well in colder climates.

There have also been many other reasons to run throughout human history before the invention of motor vehiclces. Running from encounters with predators or to catch up with herds of game in the distance. Jogging to get back from gathering to the camp before dark. Running after/away from other humans; probably a common reason throughout our history.

However: Running on hunts maybe more varied than the way most people run now; running - walking - stopping - searching for tracks - running again and so on + carrying home the kill (hopefully). Our distant ancestors had no running shoes (less stress on the body?) and were also running on earth/grass not roads. No sugary sports drinks etc. Running was probably also done by the young members of a family/group. I suspect the expectation or desire to still be running long-distances at 50 is quite new.

Is running a healthy paleolithic human activity: yes. Do you have to run to be healthy: no.

This is part of the variation and adaptability of us humans. Plus idle spectulation about the past is fun :)

Adding to gilliebean's answer, I've been exploring that very topic, too. Taking from a recent post on Free The Animal, I decided to steer back to running. It's fun for me, and part of the reason I train is the "what if". What happens if I needed to run long distances at a quick clip? I want to make sure I can do it.

A 5km-ish run before dinner a few hours after Crossfit Football yielded some interesting results. First, despite not having done a run of that distance in 4ish months, I was super fast. Being super fast makes running long distance fun. My cardio was also quite good considering the indulgence of my vices and no training for a few weeks. I've now decided to add occasional 30min runs a few hours before or after hitting non-running related CFFB.

Things that I want to explore that can help keep running more paleo are the obvious: - POSE running - Barefoot running

Just not as an over-worked and poor student.

If you are interested in a regimented approach to long-distance, take a look at Crossfit Endurance. I personally enjoy the contact-sport orientation of Crossfit Football, but I steered my roommate towards Endurance and he seems to like it. More intervals and sprint training. The approach will yield a slightly different body composition.