I'm a huge believer in the Primal Blueprint. Since adapting it in May of this year, I've lost 10 lbs (I wasn't particularly overweight beforehand) and feel and think better than I have in years. One area where I haven't followed the blueprint closely is in continuing my trail running. I felt guilty about being one of Mark's Chronic Cardio gang, but I've loved it too much to give it up, plus it FELT right intuitively.
Yesterday (10/27/09), there was an article in the NY Times that seems to support the running habit FROM A PRIMAL PERSPECTIVE. Entitled "The Human Body is Built for Distance" (http://www.nytimes.com/2009/10/27/health/27well.html), it reads almost like a chapter from Mark's book, citing anthropology, anatomy and biomechanics in support of the argument that human beings are meant to run long distances.
There are caveats, such as avoiding high-tech, highly engineered running shoes, but at its core, like Mark's book, the argument makes sense to me. I'd be interested in whether others (and Mark?) think there's enough evidence here to re-examine the rule against running.