Figure 3.

Range of CF incidences given resistance to tuberculosis in the heterozygote. The independent variables are fraction of resistance to tuberculosis in the CF carrier and percent of all deaths owing to tuberculosis prior to the pandemic that began in the 1600s. From 1600 until 1900, 20% of all deaths are ascribed to tuberculosis, as it is consistent with historical records. Light grey regions indicate combinations of parameters that could have produced the observed CF incidence (greater than 1 in 3000) in Europe. Tuberculosis resistance is a sufficient cause of CF across a broad range of parameters. In contrast, neither SDC nor typhoid fever produces sufficient CF incidence in any region of their parameter space, even allowing peak mortality levels extending back indefinitely into the past—their entire graphs are dark grey (not shown).