Image: War for Planet of the Apes

The Planet of the Apes prequels did much to explain how humans lost their status as the dominant species on the planet—a cataclysmic set of events fueled by a global pandemic known as the “Simian Flu.” This virus, the product of a medical experiment gone horribly wrong, wiped out the vast majority of humans, but it boosted the brains of apes. And in the latest installment of the franchise, the virus has mutated into an insidious new form, affecting humans in some disturbing new ways. That’s a lot for a single virus to do, prompting the inevitable question: How feasible is the Simian Flu from a scientific perspective?

Planet of the Apes may be science fiction, but there’s a surprising amount of science going on in these movies. The lab-borne virus that wiped out the majority of humanity may seem wildly improbable in terms of its effects on both humans and apes, but there’s very little in this pathogen that we haven’t seen elsewhere in nature—save for the ability to augment intelligence. What’s more, advances in biotechnology and computer science could someday allow future scientists to design and build customized viruses similar to the one shown in these films.

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To be clear, nobody’s suggesting scientists should try to make such a dangerous virus. This is merely a thought experiment to determine the scientific feasibility of the viruses portrayed in The Planet of the Apes prequels.

Complex, multi-function viruses like ALZ-112 and ALZ-113, as they’re called in the films, are unlikely to appear naturally in the wild. Typically, viruses cause impairments in their hosts, such as coughing, sneezing, diarrhea, and, in the case of rabies, an enraged, mindless urge to attack other creatures. All these things helps pathogens to proliferate, but it’s hard to see an adaptive advantage in a virus that enhances intelligence. It’s likely only scientists could create something with such an effect, not through a lab experiment gone wrong, but through intentional design.

Caesar, played by Andy Serkis, in Rise of the Planet of the Apes.

In Rise of the Planet of the Apes, fictional biotech firm Gen-Sys Laboratories created an artificial retrovirus to treat Alzheimer’s disease—which explains the pathogen’s powerful cognitive-enhancing properties.

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As revealed in the films, the first version of the drug, known as ALZ-112, showed tremendous promise in experiments with nonhuman apes and in a lone Alzheimer’s patient. The compound greatly increased the intelligence of apes, and it caused their eyes to turn green—symptoms that an infected ape could pass down to its offspring (Caesar’s mother, Bright Eyes, was treated with ALZ-112). In an effort to improve the drug, a second, more powerful variant of the strain was created, ALZ-113, but it proved fatal to most humans. The disease escaped from the lab when an ape handler became infected with the deadly strain, spreading it to an airline pilot. Caesar managed to steal several canisters of ALZ-113, which he used to increase the intelligence of his cell-mates.

Ten years later, when Dawn of the Planet of the Apes opened, a global pandemic known as the Simian Flu had wiped out the vast majority of humans. Those who survived, likely on account of a genetic immunity to the disease, lived in small, isolated pockets. Caesar, along with his uplifted primate comrades, sought shelter in the forest, where they started an ape civilization.

Two years later, in War for Planet of the Apes, a second wave of the Simian Flu began to make the rounds, but in a mutated form. The new strain didn’t kill humans outright, but it caused them to lose their ability to speak and to suffer significant declines in intelligence. The surprising appearance of Bad Ape, who was raised in a zoo, suggests the ALZ-113 virus, or a variant, has been affecting other apes outside of Caesar’s community. Neither version of the virus is fatal to nonhuman apes for reasons that aren’t entirely clear, though it may have something to do with differences in the immune systems of humans and nonhuman apes.

Nova, played by Amiah Miller, has contracted the mutated strain of ALZ-113, making her unable to speak. (Image: War For Planet of the Apes)

To summarize, ALZ-113 is a zoonotic disease transmitted through the air and capable of spreading among all species of great apes, humans included. It affects different species in different ways, including a human mortality rate of between 95 to 99 percent. The effects of the disease are heritable, suggesting the virus encodes its DNA into the germline cells of its hosts. The mutated strain that appears in War for Planet of the Apes is a bit different in that it doesn’t kill humans (probably because survivors of the Simian Flu already have genetic immunity), but it causes them to go mute and “devolve” to a more primitive mental state.

So, can a virus be designed to do all of these things? George Church, a biologist at Harvard University’s Wyss Institute, says that when it comes to biology, there’s very little that can’t be done—in theory. “The word ‘impossible’ is generally avoided in my lab with respect to technologies,” he told Gizmodo. What’s more, many of the characteristics found in these fictional viruses have already been produced by nature.

Church says that air-borne zoonotic diseases that afflict multiple species are common (e.g. bird flu and swine flu), and that a virus that produces mortality rates of 95 percent is entirely possible, pointing to untreated rabies (100 percent), smallpox (95 percent), and H5N1 (60 percent).

As noted, ALZ-113 has profoundly different effects on humans and non-human apes. Dr. Ashish Jha, director of the Harvard Global Health Institute, says that it’s common to have very different symptoms in different host species. Often times, the manifestations of a disease are driven by an animal’s immune response, which varies across species.

“The disease that arises from an infection is a combination of the nature of the viral organism plus the immune response itself,” Jha told Gizmodo. “So a single virus can absolutely give you different diseases.”

The Colonel, played by Woody Harrelson, is all too aware of the virus’s varied effects on humans and apes.

On the biotech side, Church believes that “engineering a virus to handle Alzheimer’s is plausible.” While viruses are traditionally seen as things that cause misery, scientists already use harmless, modified viruses to introduce genetic material into cells. These implanted genes can then alter the behavior of cells as a way to cure disease. In the case of Alzheimer’s, several genes are known to contribute (see the last 10 genes in this table ), so in theory, a virus could be designed to change the way these genes work. Of course, real-world scientists haven’t managed to do this yet.

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But as Church pointed out, “normally, virus-based gene therapies do not include the ability to replicate.” Which is a good point. In order to create a disease like the one portrayed in Apes, scientists would have to take a viral-based Alzheimer’s gene therapy and modify it such that it can hijack other cells, make copies of itself, and spread to a new host. The replicative strategies of the highly virulent influenza could provide inspiration.

In terms of a virus being able to boost cognitive skills, Church says that certain genes (the same ones referenced above) can influence cognition, so changes in these genes could conceivably influence brain function either positively or negatively. To impair language skills (as per the mutated strain), the “simplest explanation would be that the speech center of the brain has somehow been affected,” he said, “Likely Broca’s area.”

But even if it’s theoretically possible to engineer a highly-communicable virus that affects intelligence, what would happen when it got out of the lab and into world? It’s been said that some viruses, notably Ebola, are too deadly for their own good, wiping out their hosts far too efficiently to result in a global pandemic. This, however, may be a bit of a myth. The Black Death in the mid-14th century wiped out an estimated 30 to 60 percent of all Europeans, and the Spanish flu of 1918-19 killed about three to five percent of the world’s population, or about 50 to 100 million people.

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Jha says there’s a tension between how fatal a disease is and how many people are infected.

“If a virus kills a host quickly, its chances of spreading are reduced,” he told Gizmodo. “But it’s not too difficult to imagine a disease that takes its time with a host where it infects them for long periods of time.” He says a virus capable of killing 95 percent or more of the population is “theoretically possible,” but unlikely given the complex set of factors required for such a thing to happen.

Interestingly, he says “the bigger the outbreak, the bigger chance that the disease can mutate into something even deadlier.” Jha pointed to the recent West Africa Ebola Outbreak, where the dreaded disease had an opportunity to turn into an even deadlier form.

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Jeremy Youde, a global health expert at ANU College of Asia and the Pacific, adds that the reproductive rate of any given virus is important, but it’s deadlines is often determined by the availability and quality of the healthcare system.

“For a virus to go all Planet of the Apes on humans, it’s likely [to] need a high basic reproduction number,” Youde told Gizmodo. “It’d also be likely to be something we hadn’t seen before and something that caused basic health systems to collapse. It’s this last point—about how resilient our health systems are and whether they are able to provide any sort of treatment (or even just basic reassurance to the population)—that would have a huge effect on whether we would survive.”

It’s important to point out that all global pandemics to date have been produced by “natural” processes. This could change in the future, where an artificial virus—either accidentally or deliberately—is set loose, sparking a devastating global pandemic. Scientists have the potential to create something far worse than nature ever could, thrusting our civilization into uncharted territory as far as pandemics are concerned. Imagine an airborne version of AIDS, for example.


Needless to say, scientists don’t currently have what it takes to design and build a virus like ALZ-113. But the relevant technologies are getting there.

In 2016, scientists created synthetic bacteria with just 473 genes. (JCVI-syn3.0. Image: J. Craig Venter Institute)

Already, scientists are using computers and artificial intelligence to design powerful new drugs. Further advances in machine learning and evolutionary algorithms will dramatically cut down the amount of time it’ll take us to develop these medicines. Scientists are also building artificial chromosomes from scratch, and using computers to create entirely new forms of life. Powerful new tools like CRISPR-cas9 are enabling scientists to cut-and-paste genes directly into DNA, while the prospect of gene drives could mean we’ll eventually be able to edit the genes of animals in the wild. And that’s not to mention all the things that will be possible with further advances in artificial intelligence and molecular assembling nanotechnology.

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While all of this is interesting and certainly scary, it brings a number of real life ethical issues to mind. With this kind of biotechnological power, what can we do to prevent a virus like Simian Flu from ever being unleashed on humanity? And what steps can we as a society take now to stop such a virus from being accidentally or deliberately engineered?

It’s not too early to start thinking about such things. For example, scientists are already conducting “gain of function” experiments in which natural viruses are deliberately modified in the lab to assess how close they are to becoming a threat to humans. A few years ago, researchers determined that H5N1 (a deadly variant of the bird flu) is as little as one mutation away from becoming human-transmissible. With this knowledge, scientists are hoping to anticipate the mutation before it happens, and to develop vaccines before the human version of the disease even exists. But some scientists say it’s not worth the risk, and that accidents—where the modified virus escapes the lab—could happen. They say the data gleaned from these studies, while important, need to be protected and not broadcast to the world in popular science journals. This debate is far from settled, and it’s not immediately clear how scientists should proceed.

As time passes, however, and as our tools get even more powerful, it’s likely that regulations and restrictions will be introduced to curtail or constrain scientific work. Today we see this manifested in injunctions against creating transgenic organisms (where the genes of one species in transplanted into another) or engaging in human germline engineering, which could lead to prospective parents literally selecting the traits of their future offspring.

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Setting limits on science is obviously not ideal, but we need to stay a step ahead of our technology to prevent harm and the kind of catastrophe portrayed in The Planet of the Apes prequels. Let’s do our best to keep viruses like ALZ-113 within the realm of science fiction.