Geneticists generally use portmanteau words to describe hybrids, with the order of syllables indicating which parent is which. This is important because of genomic imprinting: genes are expressed differently depending on which parent contributed them. The names are formed according the convention first part of sire's name +second part of dam's name, except where the result is unwieldy. For geneticists, "Chuman" therefore refers to a hybrid of male chimpanzee and female human, while "Humanzee" or "manpanzee" refers to a hybrid of male human and female chimpanzee (cf.tigon/liger). This distinction is not always followed in popular speech.
Humans have one fewer pair of chromosomes than other apes, with ape chromosomes 2 and 4 fusing into a large chromosome (which contains remnants of the centromere and telomeres of the ancestral 2 and 4). Having different numbers of chromosomesis not an absolute barrier to hybridization; similar mismatches are relatively common in existing species, a phenomenon known aschromosomal polymorphism.
All great apes have similar genetic structure. Chromosomes 6, 13, 19, 21, 22, and X are structurally the same in all great apes. Chromosomes 3, 11, 14, 15, 18, and 20 match between gorillas, chimpanzees, and humans. Chimps and humans match on 1, 2p, 2q, 5, 7–10, 12, 16, and Y as well. Some older references include Y as a match between gorillas, chimps, and humans, but chimpanzees (including bonobos) and humans have recently been found to share a large transposition from chromosome 1 to Y not found in other apes. 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). 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 44 and 62 depending upon species. In a direct parallel to the chimp-human case, the Przewalski 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. In the 1920s the Soviet biologist Ilya Ivanovich Ivanov carried out a series of experiments to create a human/nonhuman ape hybrid. Working with his own sperm and female chimpanzees, he failed to create a pregnancy. In 1929 he organized 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 the Kazakh Veterinary-Zootechnical Institute and died of a stroke two years later. In 1977, researcher J. Michael Bedford discovered that human sperm could penetrate the protective outer membranes of a gibbonegg. 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. In 2006, research suggested that after the last common ancestor of humans and chimpanzees diverged into two distinct lineages, inter-lineage sex was still sufficiently common that it produced fertile hybrids for around 1.2 million years after the initial split. Still, despite speculation, no human-chimpanzee cross has ever been confirmed. Ilya Ivanovich Ivanov was the first person to attempt to create a human–ape hybrid. As early as 1910 he gave a presentation to the World Congress of Zoologists in Graz, Austria, in which he described the possibility of creating such a hybrid by artificial insemination. In 1924, while working at the Pasteur Institute in Paris, Ivanov obtained permission from the Institute's directors to use its experimental primate station in Kindia, French Guinea, for such an experiment. Ivanov attempted to gain backing for his project from the Soviet government. He dispatched letters to the People's Commissar on Education and Science Anatoliy Vasilievich Lunacharsky and to other officials. Ivanov's proposal finally sparked the interest of Nikolai Petrovich Gorbunov, the head of the Department of Scientific Institutions. In September 1925 Gorbunov helped allocate US$10,000 to the USSR Academy of Sciences (now the Russian Academy of Sciences) for Ivanov's human-ape hybridization experiments in Africa. In March 1926 Ivanov arrived at the Kindia facility, but stayed only a month without success. The Kindia site, it turned out, had no sexually mature chimpanzees. He returned to France where he arranged through correspondence with French Guinea's colonial governor to set up experiments at the botanical gardens in Conakry. Ivanov reached Conakry in November 1926 accompanied by his son, also named Ilya, who would assist him in his experiments. Ivanov supervised the capture of adult chimpanzees in the interior of the colony, which were brought to Conakry and kept in cages in the botanical gardens. On February 28, 1927, Ivanov inseminated two female chimpanzees with his own sperm.On June 25, his son inseminated a third chimpanzee with his sperm. The Ivanovs left Africa in July with thirteen chimps, including the three used in his experiments. They already knew before leaving that the first two chimpanzees had failed to become pregnant. The third died in France, and was also found not to have been pregnant. The remaining chimps were sent to a new primate station at Sukhumi. Although Ivanov attempted to organize the insemination of human females with chimpanzee sperm in Guinea, these plans met with resistance from the French colonial government and there is no evidence such an experiment was arranged there. Upon his return to the Soviet Union in 1927, Ivanov began an effort to organize hybridization experiments at Sukhumi using ape sperm and human females. Eventually in 1929, through the help of Gorbunov, he obtained the support of the Society of Materialist Biologists, a group associated with the Communist Academy.In the spring of 1929 the Society set up a commission to plan Ivanov's experiments at Sukhumi. They decided that at least five volunteer women would be needed for the project. However, in June 1929, before any inseminations had taken place, Ivanov learned that the only postpubescent male ape remaining at Sukhumi (anorangutan) had died. A new set of chimps would not arrive at Sukhumi until the summer of 1930. There have been no scientifically verified specimens of a human/ape hybrid. A performing chimp named Oliver was popularized during the 1970s as a possible chuman/humanzee, but genetic tests conducted at the University of Chicago concluded that, despite Oliver's somewhat unusual appearance and behavior, he was a normal chimpanzee: he had the same number of chromosomes as normal chimpanzees. The "hybrid" claims may merely have been a promotional gimmick. Despite the dismissal of the claim, Oliver's representational legacy persists in popular culture. The decades-long speculation about his possible human-chimp hybrid origins led to numerous references, many satirical or at least intended to be humorous. For example, the Church of the SubGenius, which has a feast day or holy day (and sometimes several) every day of the year, designates October 20 The Feast of Saint Oliver the humanzee. In addition, some musical outfits reference Oliver's legacy, such Ontario's The Humanzees. Depictions like these generally ignore or predate the proof that Oliver is not a hybrid. Oliver has been regularly discussed by Karl Pilkington on The Ricky Gervais Show, in a feature called "Monkey News". Current research into human evolution tends to confirm that in some cases, interspecies sexual activity may have been a key part of human evolution. Analysis of the species' genes in 2006 provides evidence that after human ancestors had started to diverge from chimps, interspecies mating between "proto-human" and "proto-chimps" nonetheless occurred regularly enough to change certain genes in the new gene pool: A new comparison of the human and chimp genomes suggests that after the two lineages separated, they may have begun interbreeding... A principal finding is that the X chromosomes of humans and chimps appear to have diverged about 1.2 million years more recently than the other chromosomes. The research suggests that: There were in fact two splits between the human and chimp lineages, with the first being followed by interbreeding between the two populations and then a second split. The suggestion of a hybridization has startled paleoanthropologists, who nonetheless are 'treating the new genetic data seriously'.