Rumors of a human-chimpanzee hybrid have abounded for centuries, but there hasn't been concrete proof. But then, how much proof do you actually need? Anyone who doubts that humans have fucked chimps hasn't met enough humans. Tune in to an episode of Comedy Central's "The Man Show," then tell me this hasn't happened.
Chimps and humans are so genetically similar as to be nearly indistinguishable, appearances aside. Science estimates that about 95-99% of our genetic code is identical to that of a chimpanzee. The similarity is roughly equivalent to the difference between donkeys and horses.
The practical upshot of this is that there is a very good chance that a human-chimp coupling could produce a viable offspring, just as donkeys and horses can mate to produce mules. (So don't forget to take condoms on that safari!)
So it's possible, according to the rules of science, and probable, according to human nature. So why isn't there a race of human hybrids out there wandering the earth?
Well, aside from "Who says there isn't?" one major practical consideration is fertility. It's tricky mixing species, even when they are closely related, and due to a chromosomal count issue, 99.9% of "humanzees" would be sterile, just like 99.9% of mules.
So the question isn't really whether it "can" happen or even whether it "has" happened, so much as "Can we have a look at one?"
Maybe. There have been frequent claims that one beastie or another is a "humanzee" (also known as a "sport" or a "chimera," the generic term for any combination of two genetic patterns into one individual creature). Some of the claims are more credible than others.
The most widely discussed "humanzee" sighting was a critter named "Oliver." Oliver was a sideshow star, but he wasn't like the other chimps in the traveling circus circuit. He was said to have come from somewhere in the Congo, although that claim is somewhat shrouded in mystery at this late date.
Oliver didn't like hanging out with his own alleged species and preferred the company of humans. He walked upright, he sat in chairs. He helped around the house with chores, and eventually he began hitting on the circus owner's wife, which led to his sale in 1976 to a New York lawyer named Michael Miller.
Oliver also looked different from other chimps; he less hair, a smaller chin, a smaller and rounder cranium, and pointed ears (which neither chimps nor humans normally display). Except for the latter trait, these characteristics gave him a remarkably human appearance relative to normal chimps. He also reportedly had an unusual scent, compatible neither with chimps nor humans.
According to Miller, blood tests revealed Oliver had 47 chromosomes — one more than a human and one less than a chimp. The odd number of chromosomes would also strongly suggest hybridization of some sort. (The claim was later disproved.)
Among the non-Bestiality related explanations for Oliver's freakish characteristics were mutation, spontaneous evolution and hybridization with another form of ape (such as the also-human-like bonobo, which is conveniently a sex-crazed lunatic).
In keeping with human nature, this potential ambassador to a new species was not welcomed and honored, nor was he the subject of attempts to communicate and learn. Instead, he was bounced around from "owner" to "owner," displayed as a sideshow freak, and eventually sold to a laboratory of the "pouring-pepper-juice-in-cute-little-bunny-eyes" sort.
Now, bleeding heart liberal inclinations aside, one has to seriously question the ethics of a species that is willing to imprison and torture another species with 99% of the same genes for the sake of mass-producing less-clumpy mascara, but it's even more baffling how a potentially half-human creature could be banished to this fate.
Fortunately, perhaps due to a surplus of cute little bunnies, Oliver was never required to test the effects of eating eyeliner or having suntan lotion intravenously injected. Oliver probably didn't see the bright side of this, as he was confined for seven years in a 5-by-7 cage (worse than even Camp X-Ray), until his muscles atrophied for lack of ability to move.
Oliver was retired from the lab in 1996 and sent to a chimp retirement home. He was finally called in for credible scientific testing, which insisted that he was really just a "normal chimp" with 48 chromosomes, an explanation which satisfied absolutely no one except a bunch of killjoy skeptics. Other scientists have continued to push for more research.
Oliver aside, there are some intriguing other possibilities for humanzees. For instance, consider Bigfoot and the Yeti (abominable snowman). Interspecies breeding can produce some interesting side-effects, such as in the case of the "liger," a tiger-lion hybrid which is incredibly huge, much bigger than either of its forbearers.
Could Bigfoot be some sort of human-chimp hybrid afflicted with gargantuism? Well, of course it could, but whether it's likely is another story.
Biologist Stuart Newman attempted to file a patent on human-chimp chimera genes in what he claimed was a political statement about the intellectual property rights granted to biotech companies for living creatures (the patent was rejected on the grounds that it constituted slavery, i.e., you can't own a being with human genetic material).
Whether or not you believe there are already human-chimp hybrids walking the earth, odds are pretty good that it's going to happen eventually. Scientists have already created simplistic hybrids between pigs and humans, and cows and humans. And cows and pigs are a lot less closely related to humans than chimps. The aforementioned experiments were never allowed to grow past the embryonic stage. At least, that's what they claim...