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It’s Time to Make Human-Chimp Hybrids

The humanzee is both scientifically possible and morally defensible.

It is a bit of a stretch, but by no means impossible or even unlikely that a hybrid or a chimera combining a human being and a chimpanzee…By David P. Barash

It is a bit of a stretch, but by no means impossible or even unlikely that a hybrid or a chimera combining a human being and a chimpanzee could be produced in a laboratory. After all, human and chimp (or bonobo) share, by most estimates, roughly 99 percent of their nuclear DNA. Granted this 1 percent difference presumably involves some key alleles, the new gene-editing tool CRISPR offers the prospect (for some, the nightmare) of adding and deleting targeted genes as desired. As a result, it is not unreasonable to foresee the possibility—eventually, perhaps, the likelihood—of producing “humanzees” or “chimphumans.” Such an individual would not be an exact equal-parts-of-each combination, but would be neither human nor chimp: rather, something in between.

If that prospect isn’t shocking enough, here is an even more controversial suggestion: Doing so would be a terrific idea.


The year 2018 is the bicentennial of Mary Shelley’s Frankenstein, subtitled the modern Prometheus. Haven’t we learned that Promethean hubris leads only to disaster, as did the efforts of the fictional Dr. Frankenstein? But there are also other disasters, currently ongoing, such as the grotesque abuse of nonhuman animals, facilitated by what might well be the most hurtful theologically-driven myth of all times: that human beings are discontinuous from the rest of the natural world, since we were specially created and endowed with souls, whereas “they”—all other creatures—were not.

Book cover of Frankenstein.Bernie Wrightson

Of course, all that we know of evolution (and by now, it’s a lot) demands otherwise, since evolution’s most fundamental take-home message is continuity. And it is in fact because of continuity—especially those shared genes—that humanzees or chimphumans could likely be produced. Moreover, I propose that the fundamental take-home message of such creation would be to drive a stake into the heart of that destructive disinformation campaign of discontinuity, of human hegemony over all other living things. There is an immense pile of evidence already demonstrating continuity, including but not limited to physiology, genetics, anatomy, embryology, and paleontology, but it is almost impossible to imagine how the most die-hard advocate of humans having a discontinuously unique biological status could continue to maintain this position if confronted with a real, functioning, human-chimp combination.1

It is also possible, however, that my suggestion is doubly fanciful, not only with respect to its biological feasibility, but also whether such a “creation” would have the impact that I propose—and hope. Thus, chimpanzees are widely known to be very similar to human beings: They make and use tools, engage in complex social behavior (including elaborate communication and long-lasting mother-offspring bonds), they laugh, grieve, and affirmatively reconcile after conflicts. They even look like us. Although such recognition has contributed to outrage about abusing chimps—as well as other primates in particular—in circus acts, laboratory experiments, and so forth, it has not generated notable resistance to hunting, imprisoning and eating other animal species, which, along with chimps themselves, are still considered by most people to be “other” and not aspects of “ourselves.” (Chimps, moreover, are enthusiastically consumed in parts of equatorial Africa, where they are a prized component of “bush meat.”)

It is at least arguable that the ultimate benefit of teaching human beings their true nature would be worth the sacrifice paid by a few unfortunates.

In his book, Less Than Human: Why We Demean, Enslave, and Exterminate Others, David Livingstone Smith examined how dehumanization goes hand-in-hand with racism and genocide. Smith revealed a long-standing pattern whereby people, despite acknowledging that other human beings appear to be human, often maintain that in their essence—whatever that means—these others continue to be less than human. It is thus entirely possible that comparably stubborn biases will persist even if our biological continuity with other living things becomes undeniable. Moreover, people are certainly known to obscure inconvenient truths: It is said that when the wife of the Bishop of Worcester heard of Darwin’s scandalous theory, she exclaimed “Descended from apes? My dear, let us hope that it isn’t true, but if it is true, let us hope that it does not become widely known!”

On the other hand, it seems equally likely that faced with individuals who are clearly intermediate between human and ape, it will become painfully obvious that a rigid distinction between the two is no longer tenable. But what about those presumably unfortunate individuals thereby produced? Neither fish nor fowl, wouldn’t they find themselves intolerably unspecified and inchoate, doomed to a living hell of biological and social indeterminacy? This is possible, but it is at least arguable that the ultimate benefit of teaching human beings their true nature would be worth the sacrifice paid by a few unfortunates. It is also arguable, moreover, that such individuals might not be so unfortunate at all. For every chimphuman or humanzee frustrated by her inability to write a poem or program a computer, there could equally be one delighted by her ability to do so while swinging from a tree branch. And—more important—for any human being currently insistent upon his or her species’ specialness, to the ultimate detriment of literally millions of other individuals of millions of other species, such a development could well be a real mind expander and paradigm buster.


In the early days of biology, when special creation ruled, it was widely thought that species were rigid and fixed, each specially created as such. Now we know better. As currently recognized, a species is a group of naturally interbreeding individuals; that is, a population within which genes are regularly exchanged. Moreover, even though people like to think in terms of yes/no, either/or dichotomies, we also know that the boundaries between species are shifting and flexible: e.g., perfectly “good” species such as mallards and pintail ducks often interbreed, producing hybrids that can be the bane of even experienced birders. Grizzlies and polar bears also hybridize on occasion, producing “grolar” bears.

A recent study of the genomes of ravens—which occupy much of the Northern Hemisphere—found that this species had earlier divided into two, with a smaller population limited to California. Then these two raven species recombined several hundred thousand years ago, forming the single Holarctic raven species that we know today.1 Such “speciation reversal” may well be a more widespread phenomenon than previously thought. Elephants and mastodons evidently interbred before the latter went extinct.2 Wolves, coyotes, and domestic dogs have been hybridizing in recent decades, and it is clear that some populations of modern Homo sapiens contain as much as 5 percent Neanderthal genes, and some or all of us may also harbor an unknown soupcon from those mysterious hominins known as Denisovans. Princeton evolutionary biologist Rosemary Grant—who, along with her husband Peter, has long studied speciation among Galapagos finches—suggests that many animal species (including ourselves) are likely “haunted by the ghosts of interbreeding past.”

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The possibility thus cannot be excluded that combining human and chimp may herald, or threaten, something biologically new on our—and their—horizon.

A hybrid is a cross between individuals of distinct genetic ancestry, which means that technically, nearly everyone is a hybrid, except for clones, identical twins, or perhaps persons produced by close incest. More usefully, we speak of hybridization as the process by which members of different sub-species are crossed (mating Labradors and poodles, for example, to produce labradoodles), or—more rarely—different species, in which case the resulting hybrids are often nonviable, either sterile (e.g., mules, hybrids made by crossing horses and donkeys), or just plain unusual (e.g., tigrons, which have occasionally been generated by hybridizing tigers and lions, or ligers, produced vice versa). Hybrids are genetic mixtures, with essentially all body cells containing equal quantities of DNA from each parent. This, of course, is true of all sexually produced individuals, it’s just that with hybrids, those two parents are likely to be more distantly related than is usual.

These days, a humanzee or chimphuman is not beyond imagining.

Chimeras, on the other hand, are somewhat different. They derive from what is essentially a process of grafting, whereby two genetic lines (most interestingly, different species) are combined to produce an individual that is partly of one genotype and partly of another, depending on which cells are sampled, and at what point in embryonic development. Probably because it is easier to imagine creatures produced by combining identifiable body parts from different animals than to picture a mingled, intermediate form, chimeras, more than hybrids, have long populated the human imagination. Ganesh, the Hindu god with a human body and elephant’s head, is a chimera, as are the horse-human centaurs of Western mythology. The classic “chimera” of Greek legend had the head and body of a lion, a tail that had morphed into the head of a snake and—to make a weird creature even more so—the head of a goat, sometimes facing forward and sometimes backward.

It is unclear whether my own imagined chimphuman will be a hybrid (produced by cross-fertilizing human and non-human gametes), or a chimera, created in a laboratory via techniques of genetic manipulation. I’m betting on the latter. Either way, human-chimp mixtures aren’t a new idea.

During the 1920s, a Russian biologist with the marvelously Slavic name Ilya Ivanovich Ivanov appears to have made the first serious, scientifically informed efforts to create a genetic hybrid between chimpanzees and human beings. Ivanov had the perfect qualifications: Not only did he possess a special interest in creating interspecific hybrids, he was an early specialist in artificial insemination, who had achieved international renown as a successful pioneer when it came to horse breeding. Prior to his work, even the most prized stallions and mares were limited to reproducing by “natural cover”—i.e., the old-fashioned way, one mounting at a time. But Ivanov found that by appropriate and careful dilution of stallion semen, combined with adroit use of the equine equivalent of a turkey baster, he could generate as many as 500 foals from a single genetically well-endowed stallion. His achievement caused a worldwide sensation, but nothing compared to what he next attempted.

And failed.

Ilya Ivanovic IvanovWikimedia

It happened initially at the Research Institute of Medical Primatology, the oldest primate research center in the world, located at Sukhumi, the capital of Abkhasia, currently a disputed region in the state of Georgia, along the Black Sea. At one time, the Sukhumi Institute was the largest facility conducting research on primates. Not coincidentally, Stalin is believed to have been interested in such efforts, with an eye toward developing the “new Soviet man” (or half-man, or half-woman).

Nor was Soviet interest in combining human and nonhuman genetic material limited to Russian biologists. The novelist Mikhail Bulgakov, best known—at least in the West—for his fantasy, The Master and Margarita, also wrote Heart of a Dog, a biting satire on early Soviet-era social climbers, in which a pituitary gland from a drunken person is implanted into a stray dog, who subsequently becomes more and more human—although not noticeably more humane as he proceeds to eliminate all “vagrant quadrupeds” (cats) from the city. Maxim Gorky was on board, writing approvingly that Lenin and his Bolshevik allies were “producing a most severe scientific experiment on the body of Russia,” which would eventually achieve “the modification of human material.”

Similar modification became a staple of Soviet biology, as well, as when S.A. Voronov attempted “rejuvenation therapy,” a series of failed attempts to restore sexual function in rich, elderly men by transplanting slices of ape testes. But it was Ivanov who made the most serious efforts at combining human and nonhuman apes. Earlier in his career, in addition to the successful artificial insemination of horses, Ivanov had created a variety of animal hybrids, including “zeedonks” (zebras + donkeys) and different combinations of small rodents (mice, rats, and guinea pigs). For a time in the 1990s a fictional version of Ivanov was the chief character in a Russian-era television show portraying him as the “Red Frankenstein.”

In 1910, Ivanov had announced, at a World Congress of Zoologists in Graz, Austria, that it might be possible to produce a human-ape hybrid via artificial insemination. During the mid-1920s, working at a laboratory in Conakry (then part of French Guinea) under the auspices of France’s highly respected Pasteur Institute, Ivanov attempted just that, seeking without success to inseminate female chimpanzees with human sperm. (We don’t know whose, and we also presume—although don’t know for certain—that the attempted insemination was by artificial rather than natural means.) Then, in 1929, at the newly established Sukhumi Primate Research Institute, he endeavored to reverse donor and recipient, having obtained consent from five women volunteers to be inseminated—once again, presumably by artificial methods rather than “natural cover”—with sperm from chimpanzees and orangutans. Inconveniently, however, the nonhuman primate donors died before making their “donations,” and for reasons that are unclear, Ivanov himself fell out of political favor and was sent to Siberia in 1930; he died a few years later.

All sorts of things can be done; whether they should, is another question.

No one knows precisely what motivated Ilya Ivanov’s early fertilization experiments. Maybe it was the allure of the possible, such that having discovered the potent hybrid-generating hammer of in vitro fertilization, everything—including eggs and sperm, with one from human and the counterpart from nonhuman primates—looked alluringly like a nail. Or maybe he was driven by the prospect of currying favor with Stalin, or of fame (or infamy) had he succeeded, or perhaps as an ardent atheist Bolshevik Ivanov was inspired by the prospect of disproving religious dogma.

In any event, Ivanov’s story is not especially well known outside Russia, and insofar as Westerners learn of it, they are inclined to ridicule it as an absurd episode of reaching for a would-be “planet of the (communist) apes,” or to inveigh against the immorality of such at attempt, which is increasingly feasible. To be sure, his crude efforts at cross-species hybridization are at present no closer to fruition, simply because even though human and chimp DNA are overwhelmingly similar, humans have 46 chromosomes whereas chimps have 48, so getting sperm from either species to combine with eggs from the other to produce viable offspring is—to put it literally—inconceivable.

These days, however, a humanzee or chimphuman is not beyond imagining. There have been many advances in biomedical research that not only emphasize the continuity between human beings and other animals, but that do so explicitly in the interest of human betterment. Research efforts are currently underway seeking to produce organs (kidneys, livers, etc.) that develop within an animal’s body—pigs are the preferred target species—and whose genetic fingerprints are sufficiently close to the Homo sapiens counterpart to be accepted by a human recipient’s immune system, while also able to function in lieu of the recipient’s damaged organ. A human skin cell, for example, can be biochemically induced to become a “pluripotent stem cell,” capable of differentiating into any human tissue type. If, say, a replacement liver is desired, these stem cells can be introduced into a pig embryo after first using CRISPR to inactivate the embryo’s liver-producing genes. If all goes well, the resulting pig-human chimera will have the body of a pig, but containing an essentially human liver, which would then be available for transplantation into a person whose liver is failing.

After years of opposition, the U.S. National Institutes of Health announced in August, 2016 that it intends to lift its moratorium on stem cell research, which holds out promise for treating (perhaps even curing) many serious human diseases, such as cirrhosis, diabetes, and Parkinson’s. Currently prohibited—and likely to remain so—is funding for studies that involve injecting human stem cells into embryonic primates, although inserting such cells into adults is permissible. Insofar as there is a biological line separating human beings from other species, it should be clear that this line is definitely permeable, not hard and fast, and is based more on ethical and political judgment than on science or technology. All sorts of things can be done; whether they should, is another question.


Looking favorably on the prospect of a humanzee or chimphuman will likely be not only controversial, but to many people, downright immoral. But I propose that generating humanzees or chimphumans would be not only ethical, but profoundly so, even if there were no prospects of enhancing human welfare. How could even the most determinedly homo-centric, animal-denigrating religious fundamentalist maintain that God created us in his image and that we and we alone harbor a spark of the divine, distinct from all other life forms, once confronted with living beings that are indisputably intermediate between human and non-human?

In any event, the nonsensical insistence that human beings are uniquely created in God’s image and endowed with a soul, whereas other living things are mere brutes has not only permitted but encouraged an attitude toward the natural world in general and other animals in particular that has been at best indifferent and more often, downright antagonistic, jingoistic, and in many cases, intolerably cruel. It is only because of this self-serving myth that some people have been able to justify keeping other animals in such hideous conditions as factory farms in which they are literally unable to turn around, not to mention prevented from experiencing anything approaching a fulfilling life. It is only because of this self-serving myth that some people accord the embryos of Homo sapiens a special place as persons-in-waiting, magically endowed with a notable humanity that entitles them to special legal and moral consideration unavailable to our nonhuman kin. It is only because of this self-serving myth that many people have been able to deny the screamingly evident evolutionary connectedness between themselves and other life forms.

When claims are made about the “right to life,” invariably the referent is human life, a rigid distinction only possible because of the presumption that human life is somehow uniquely distinct from other forms of life, even though everything we know of biology demonstrates that this is simply untrue. What better, clearer, and more unambiguous way to demonstrate this than by creating viable organisms that are neither human nor animal but certifiably intermediate?


David P. Barash is professor of psychology emeritus at the University of Washington. This article is somewhat modified from a chapter in his next book—Through a Glass Brightly: Using Science to See Our Species as It Really Is—which will be published summer, 2018, by Oxford University Press.


References

1. Kelarns, A., et al.  Genomic evidence of speciation reversal in ravens. Nature Communications 9 (2018). Retrieved from doi:10.1038/s41467-018-03294-w

2. Palkopoulou, E., et al. A comprehensive genomic history of extinct and living elephants. Proceedings of the National Academy of Sciences (2018). Retrieved from doi:10.1073/pnas.1720554115

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