FIGURE 2. The distributions for the ages of the youngest clade contributing to a significant inference of gene flow constrained by isolation by distance at the highest nesting level for the genes MX1, PDHA1, EDN and ECP, and at intermediate nesting levels for the 
-globin (-Hb) locus and the Xq13.3 region.
From the following article:
Alan Templeton
Nature 416, 45-51(7 March 2002)
doi:10.1038/416045a
The x axis gives the time in millions of years before present (bp), and the y axis gives the gamma probability distribution, f(t), that was fitted to the clade data.
