You can see similar trends in other non-agrarian societies.
http://www.gapminder.org/world/#$majorMode=chart$is;shi=t;ly...,
There are studies that go along with your POV
http://www.anth.ucsb.edu/faculty/gurven/papers/GurvenKaplan2...
but they are, to date, very much in the minority of research in the area.
The other component of that is of course that we're all fat and out of shape today because we eat foods that cavemen never had access to.
One measure of health is of course weight, but so is life expectancy. If we follow a life-plan where we're around some normal weight but die at 30 I'm not sure that's a great plan. We evolved to die around 30, most research into aging agrees with this (some say ~40), and that's "natural" I suppose, but I think I reject that notion that we should only do things in the modern world that fit what we were required to do a million years ago because it's what we evolved to cope with and eek out 3 or 4 decades of life.
Another is infant mortality, we evolved to reproduce pretty fast because we evolved to maintain population with lots of dead infants. We also evolved to produce slightly more males than females since men die faster, which is okay since fewer men can reproduce with more women.
We also evolved to be able to bear children in our early teens, to grow beards, hair and nails, and to have bad eyesight in some large percentage of the population. Should we lower the age of consent to 13? Not shave or cut our hair or nails ever and not wear glasses?
I'm not sure any of these notions work today, but extending the central argument out:
If we should eat like our ancient ancestors did since we evolved to eat like that and therefore it must be healthy, should we not live like our ancient ancestors did since therefore that must be equally valid by the "it's all natural so it's good" principle?
And I think it's a straw man to say that accepting a "caveman" or "hunter gatherer" diet means we need to accept -every- aspect of "primitive" life.
EDIT: http://www.anth.ucsb.edu/faculty/gurven/papers/pdrdraft04182...
"I think it's closer to the truth to say that cavemen...lived a natural lifespan closer to modern man." Test it! I honestly don't know the answer, the data I managed to find in 10 minutes of searching says that hypothesis is incorrect -- but as you rightly point out my data includes infant mortality in the averages (I believe). But if you can find data that says "excluding infant mortality, pre-agrarian cultures have an average lifespan of 70-80 years" I'll be more than happy to accept that.
http://en.wikipedia.org/wiki/Life_expectancy
According to the entry above, there's a measure called e5 that should supply the relevant figures.
And I think it's a straw man to say that accepting a "caveman" or "hunter gatherer" diet means we need to accept -every- aspect of "primitive" life.
I'm not really attacking the diet per se, many of the recipes are actually pretty tasty and are generally pretty healthy. I'm attacking the faulty line of reasoning given as to why one should do this.
"it seems to be pretty healthy" is wishy washy, but okay
"You should eat this way because evolution made you to eat this way therefore it's healthy" is not, it present a long chain of reasoning that falls apart at almost every link, but it's presented as a kind of science, which it's not by this reasoning.