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 ferus przewalskii) with 33 chromosome pairs, and the domestic horse (E. f. caballus) with 32 pairs, have been found to be interfertile, and produce semi-fertile offspring: male hybrids can breed with female domestic horses. In 1977, researcher J. Michael Bedford 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 Homo sapiens sapiens alone, it is probably restricted to the Hominoidea. However, in the opposite direction of closely related species, it has been found that human sperm binds to gorilla oocytes with almost the same ease as to human ones. Hybridization between members of different, but related genera is sometimes possible, as in the case of cama (camel and llama), wholphin (common bottlenose dolphin and false killer whale), and some felid hybrids, for example. Reports of attempted hybridization There have been no scientifically verified specimens of a human–chimpanzee hybrid, but there have been substantiated reports of unsuccessful attempts to create one in the Soviet Union in the 1920s, and various unsubstantiated reports on similar attempts during the second half of the 20th century. Ilya Ivanov was the first person to attempt to create a human–chimpanzee hybrid by artificial insemination. Ivanov outlined his idea as early as 1910 in a presentation to the World Congress of Zoologists in Graz. In the 1920s, Ivanov carried out a series of experiments, culminating in inseminating three female chimpanzees with human sperm, but he failed to achieve a pregnancy. These initial experiments took place in French Guinea. (For comparison with known cama statistics, in the case of male camel–female guanaco cross the probability that insemination would lead to pregnancy was approximately 1/6.) In 1929 he attempted to organize a set of experiments involving nonhuman ape sperm and human volunteers, but was delayed by the death of his last orangutan. The next year he fell under political criticism from the Soviet government and was sentenced to exile in the Kazakh SSR; he worked there at