The humanzee (Homo sapiens sapiens x Pan troglodytes) (also known as the Chuman or Manpanzee) is a hypothetical chimpanzee/human hybrid. Chimpanzees and humans are closely related (sharing 95% of their DNA sequence and 99% of coding DNA sequences), leading to contested speculation that a hybrid is possible. However, such a human-animal hybrid has not actually existed outside of fictional works that have explored the concept.
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 pair fewer 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 chromosomes is not an absolute barrier to hybridization; similar mismatches are relatively common in existing species, a phenomenon known as chromosomal 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 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.
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 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.
The Ivanov experiments
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 the 1920s, Ivanov carried out a series of experiments to create a human/nonhuman ape hybrid. Working with human 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.
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. A geneticist from the University of Chicago examined Oliver's chromosomes in 1996 and revealed that Oliver had forty-eight, not forty-seven, chromosomes, thus disproving the earlier claim that he did not have a normal chromosome count for a chimpanzee. Oliver's cranial morphology, ear shape, freckles and baldness fall within the range of variability exhibited by the Common Chimpanzee. Scientists performed further studies with Oliver, the results of which were published in the American Journal of Physical Anthropology.
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,
- 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'.
For a chromosomal homology map between these species see.
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- New York Times article Two Splits Between Human and Chimp Lines Suggested (May 2006).
- The Atlantic article Oliver's Travels
- Graphic for two-split theory
- New York Times review of the novel, Lucy, by Laurence Gonzales