This is an oft misunderstood statistic. Life expectancy stats measure the average of a group...not an individual. Life expectancy increases are due in large part because of better infant healthcare (far, far fewer babies die today) and the benefits of clean water, available food sources, and ability to keep common diseases at bay with vaccines. That...and while we haven't wiped out warfare, we aren't routinely having to defend our territories or families to the death. If a human could avoid all the aforementioned former pitfalls, they generally lived as long as we do now (at least looking back a couple thousand years)> Much like the faulty studies testing the effects of eating red meat within diets (which none are ever done without also consuming the other Standard American diet garbage), you can't really compare life expectancy across generations because you can't control for the environment....at least to effectively measure how consuming fatty meats did or did not affect longevity. Just too many unrelated factors that could play into this.