Didn't Our Primal Ancestors Only Live To Be 30?

So, Jenn and I have been eating "Paleo" for over a month now. I've lost 25 lbs. in 5 weeks! It's been amazing to say the least. This is sometimes called the "caveman diet". When we discuss this with people they keep bringing up the short average lifespan of primitive humans, so why would we want to look to them for lifestyle advice?

Understand that the average (being the keyword) shorter lifespan was due to many factors. Largely, child birth was not easy to survive for mother or child. Many died before their lives even began. In fact, if they lived to be 20, their life expectancy was closer to ours now. Also, the absence of modern medicine which these days keeps us safe from hundreds of ailments, diseases, viruses etc. was a huge cause of early deaths. A simple broken bone or cut could be life threatening, not to mention possible infection. They were more vulnerable to predatory animals, and lack of sufficient shelter often left them open to the elements.

The fact is that once agriculture was introduced (grains, dairy, legumes, etc.) many negative trends in human development started to occur. Smaller jaws, smaller sinus cavities, shorter, weaker bones, tooth decay, heart disease. We evolved over millions of years to eat the diet of a hunter/gatherer. Only the last 10,000 have we been eating the kinds of foods we eat so much of now. That's about .5% of our human evolution. Our bodies do not know what to do with this crap. And only over the last 50 have we been eating the refined, manufactured, engineered "foods" most of us live off of today! No wonder we are fatter and sicker than ever.