In all, 86 per cent of the increased life expectancy was due to decreases in infectious diseases. And the bulk of the decline in infectious disease deaths occurred prior to the age of antibiotics. Less than 4 per cent of the total improvement in life expectancy since 1700s can be credited to twentieth-century advances in medical care.
Reading is not a straightforward linear movement, a merely cumulative affair: our initial speculations generate a frame of reference within which to interpret what comes next, but what comes next may retrospectively transform our original understanding, highlighting some features of it and backgrounding others.