How Do We Know What We Know?

The Return of Martin Guerre by Natalie Zemon Davis How do we know what we know about history?  At some point all of us ought to have wondered how we know what we know about what happened in the past. I first wondered about this concept one day back in 2005 while listening to a story on NPR in which the interviewee, a university professor, repeated, almost off the cuff, the oft heard statement that in the middle ages life expectancy was somewhere in the mid 30 year range. I had recently read a Psalm that said the lifespan of a man was 70 years, 80 if he is strong. It occurred to me that the biblical account sounded pretty close to our modern life expectancy. Which was correct? And what happened in the more than 2,500 year interim to make people accept the modern short-life-span narrative? That day I started looking through the historical literature to figure out how we know what we know about history and life expectancy. It turns out that when controlling for infant mortality, even in the midst of war, life expectancies were astonishingly consistent throughout the centuries. We know that from contemporary records of the day, records far more numerous than we allow ourselves to imagine today. In most of Europe, peoples’ births, weddings and deaths were recorded by their local parish. Yet today we can’t imagine that people kept detailed records because we have built up fictional narratives about what our predecessors must have been like rather than reading the actual accounts. […]