It's also important to make a distinction between "the human body evolved to run long distances" and "the human body is well-suited to running and doing it for long distances is good for you". The latter seems like something we can (and should try to) prove now, without relying on the past for evidence. Knowing how our ancestors lived is nice but I'm personally more interested in knowing what's good for me, here, now.

If I recall correctly, Ardi had an opposable big toe and although he was bipedial, he couldn't have walked or run like us. If "Born to Run" is correct then Ardi represents a point in our lineage after bipediality developed, but before we evolved to become runners.

Curious if you've read the book (I haven't) and why you think that an entire tribe of people where 70 year old men regularly run 30-50 miles is not "proof" in your eyes?

Yes, I've read the book, and I would recommend it. The book makes multiple claims: The first is that given the proper environment (physical & mental fitness), we can run very long distances. This I think it proves very well with the Tarahumara tribe example.

It then goes on to make the claim that humans evolved to run long distances, in order to do persistence hunting. Persistence hunting is basically outrunning an animal for long distances so that it just drops down because it is tired. While persistence hunting itself exists, it is a stretch to say that this is how humans evolved.

The Ardi discovery that made news a few months ago shows that Ardi's environment was not really the savannah, but something that had far more trees. Persistence hunting requires a savannah like environment.

In the end, all I'm saying is that it is ok to say that humans can run long distances, but saying humans evolved to do that is far trickier and requires a lot more proof. The scientists involved in the Ardi discovery do not make any claims at all (after 15 years of studying fossils in one region). They are far more humble, and say that many different scenarios are possible.

Popular book writers on the other hand have to explain things to a lay audience, and usually provide one point of view (which typically fits their own mental model). Confirmation bias is usually rampant.

It's probably about as easy to lay out a big case that humans evolved for rock climbing and swimming. We out perform plenty of animals at that.

When you compare the meat yield of persistence hunting vs. rock climbing, PH's case does come out quite stronger.

I doubt anybody has empirically compared anything with regard to persistence hunting.

Might as well talk about meat yields of diving for shellfish. Some people think this was a major human activity.

It's all supposition.

Well, we do have a rather pronounced diving reflex.

I was under the impression that ours was one of the weakest of the mammals...

Compared to marine mammals yes. But I've read someplace that ours is remarkably strong for a supposedly completely non-aquatic mammal.

Cleaned up to be less confrontational.

There is a difference in stride efficiency between jogging and running at high speed. 20 year old men don't run 50 miles in one go let alone 70 year old men. Now jogging that distance over several hours is a reasonable form of transportation, but running is out of the question. So, jogging is a way to trade energy for time and distance where running trades endurance / distance for time, energy, and speed.

I would assume if humans where built purely for distance running then our most efficient stride would be used for distance running. But, I don't know what the overall tradeoffs are.

PS: There seems to be two definitions of running one of which is a stride there all feet leave the ground at the same time and the other involves high speed. While skipping falls under this definition of running the implication of speed is missing.