Figure 3. Inter-breeding between Rani (a) and Siswoyo (b) with native males is known to have resulted in hybridized offspring.

To illustrate subsequent introgression, this diagram is based on the assumption that 50% of alleles native to each subspecies are always uniformly inherited: thus, by example, ‘Rimba’ is three-quarters Pongo pygmaeus wurmbii and one quarter P. p. pygmaeus. The figure illustrates examples of the extent of admixture known to have occurred within and between these lineages over multiple generations. In practice, as detailed in the text, Rani’s direct descendants number(ed) at least 14 hybridized and/or introgressed individuals over 3 generations; Siswoyo’s number(ed) at least 8 over 2 generations. At least 9 of their combined descendants are males likely capable of fathering offspring. Their reproductive output is unknown, but has inevitably resulted in further admixture in other lineages.