headfirst: That’s a bit of a misleading statistic. Our ancesters average age was indeed close to 30 years but this is mainly due to lack of modern medicine (antibiotics being a major one – every cut, scrape and sexual conquest could lead to death by infection), high levels of death during pregancy/infancy, and other dangers from not living in secure accomodation, etc.
To look at another evolutionary clue, ask why would a modern human female’s menopause begin in their late 50’s early 60’s if we were only meant to live until we were 35?
A good analogy is dental care:
Modern times. More likely to get a cavity/root canal because of the increased sugars especially in drinks consumed. Solution is to go to the dentist when it happens and get it fixed.
Ancestral times: Less likely to get a cavity/root canal but if you do then no dentistry and no antibiotics and so it might end up killing you through infection or not being able to eat.
Conclusion: Far healthier ancestrally (evidence of tooth decay in found remains is incredibly low) but likely to have more severe health consequences when you do have an issue because of lack of medicine.
So….. Why not combine the two – ancestral food/exercise choices and modern medicine?