What convinces us our knowledge is so final?

If I called myself an atheist at twenty, and an agnostic at fifty and sixty, it isn’t because I’ve acquired more knowledge in the meantime: just more awareness of ignorance. How can we be sure that we know enough to know? As twenty-first century neo-Darwinian materialists, convinced that the meaning and mechanism of life have only been fully clear since the year 1859, we hold ourselves categorically wiser than those credulous knee-benders who, a speck of time away, believed in divine purpose, an ordered world, resurrection and a Last Judgment. But although we are more informed, we are no more evolved, and certainly no more intelligent than them. What convinces us our knowledge is so final?
Julian Barnes, Nothing to Be Frightened Of (London: Jonathan Cape, 2008), 23-24.