While this argument may seem to make perfect sense – and represents conventional wisdom on the subject of prehistoric longevity – it's simply wrong that the human "life span" was much shorter then than it is now. "Average longevity" was shorter, but that's something else.

Average longevity is calculated by taking the age of death of all the skeletons archaeologists find and averaging them out. There are lots of problems with this method, including the fact that once the wisdom teeth stop growing (around age 35), it's very hard to tell how old someone was when they died 25,000 years ago. The other problem is that for various reasons, a lot of babies died. So the average age of death normally cited (25 or 30) is based on a misleading calculation using suspect data.

In fact, as we detail in the book, once they got through infancy, most people in prehistory lived well into their 60s and even 70s, as foragers do today.

Remember, it's the Old Testament that says man's allotted time on Earth is "three score and ten" (=70). There was no "modern medicine" available to the people who came up with that number!