inseminera ap-sperma på en kvinna

This degree of chromosomal similarity is roughly equivalent to that found in equines. Interfertility of horses and donkeys is common, although sterility of the offspring (mules) is nearly universal (with only around 60 exceptions recorded in equine history[7]). Similar complexities and prevalent sterility pertain to horse–zebra hybrids, or zorses, whose chromosomal disparity is very wide, with horses typically having 32 chromosome pairs and zebras between 16 and 23 depending on species. In a direct parallel to the chimp–human case, the Przewalski's Horse (Equus przewalskii) with 33 chromosome pairs, and the domestic horse (E. caballus) with 32 pairs, have been found to be interfertile, and produce semi-fertile offspring: male hybrids can breed with female domestic horses.[8]

In 1977, researcher J. Michael Bedford[9] accidentally discovered that human sperm could penetrate the protective outer membranes of a gibbon egg. Bedford's paper also stated that human spermatozoa would not even attach to the zona surface of non-hominoid primates (baboon, rhesus monkey, and squirrel monkey), concluding that although the specificity of human spermatozoa is not confined to man alone, it is probably restricted to the Hominoidea.