Accusations that epidemics or pandemics are “biological warfare” are not new. Humans rightly have an innate fear of disease. “This plague is a deliberate attack” is a trope that is thousands of years old. Disease outbreaks have long been blamed on convenient scapegoats, from medieval plagues, which were often blamed on the Jews or heretics, to more recent conspiracy theories.

Misguided as such speculation has typically been, biological warfare is a real subject and nations have dabbled in development of bioweapons. Biological weapons are “public health in reverse” to quote Gen. William Creasy, a former head of the U.S. Army Chemical Corps. Plagues, in theory, could be man-made.

The current covid-19 crisis has included accusations of biological warfare. The presence of an advanced virology lab in Wuhan fed some theories and accusations that China had deliberately unleashed an attack. Some Chinese and Iranian commentators, meanwhile, claim it was an American attack. Further on the fringes, allegations that it is a weapon directed against Muslims or Israel have appeared. Is there any truth to these rumors and accusations?

The answer is no, for a variety of reasons, both scientific and practical. It starts with the basic facts of virology and genetics: The very premise that a virus must be man-made simply because it is bad is the height of anthropocentric hubris. Nature has many millions of years making viruses and it is most capable of making viral horrors on its own without help. When it comes to man-made viruses, this is a field that is only decades old. Laboratories do not create viruses as neatly or as handily as mother nature does, and it’s easy enough to demonstrate that a given virus isn’t some Frankenstein creation stitched together out of RNA or DNA from other things. For that is what a man-made virus looks like. Genetic analysis shows this virus is not man-made.

Beyond the science, however, there are practical reasons covid-19 biowarfare claims make no sense. We can look at history, military strategy and geopolitics as well as the life sciences. Biological warfare and biological weapons are an arcane subject little understood by the public. Indeed, public knowledge in this area seems to be far more based on science-fiction novels and films than on the actual history of the subject. During the Cold War, both East and West spent money and scientific effort on biological warfare in a clandestine arms race. I was privileged that in the 1990s and early 2000s I got to know the last remaining U.S. biological weapons specialists (the program ended in 1970) and also got to speak to defectors from the Soviet program. As I learned from them, biological warfare is actually a tedious and expensive business.

In science fiction, biological warfare agents are doomsday weapons designed to bring the globe to its knees. In the real world, those who developed biological weapons never aimed to produce pandemics. Instead, they expended time, money and effort toward concrete projects and understandable objects, not chaos for the sake of chaos.

Even in the 1950s and 1960s, arguably the heyday of biowarfare research, the proponents of biological warfare understood and held to a basic principle: You don’t want the bad disease you made to come back and make your own people sick. The world was less interconnected back then and the scenarios for warfare at the time did not foresee much, if any, travel between combatant countries. But the risk of accidental exposure to one’s own troops was considered too high to risk messing around with things that could not be mitigated. Today, there is a massive amount of world travel and commerce, including between potential combatants, but those old lessons have not been forgotten. Economies and supply chains are complex and intertwined, and no country would willingly engineer a weapon that would risk disrupting them.

When you look at the agents that were developed in the old days, both in the East and West, you see things such as anthrax, botulism toxin, tularemia, Q-fever, Venezuelan equine encephalitis and a variety of pestilences that afflict agriculture. Indeed, a very high percentage of the U.S. program was anti-agricultural and not intended to make people ill. These agents could be delivered as aerosols — mists of droplets or particles — but were not easily contagious from person to person. This meant that they could be targeted. Even the best biological weapons were wildly inefficient and unpredictable, but not in ways that were likely to make them blaze wildly through whole populations. The vast majority of the microbes died in storage, in transit or upon dispersal, so there was a whole esoteric discipline of biological target analysis to make sure that one’s expensive bioweapons were used properly.

On occasion, governments did work on agents that were contagious from person to person. But such work nearly always involved agents such as plague and smallpox where there were drugs or vaccines that could protect a friendly population. There is a concept in epidemiology called the Basic Reproduction Number (R0), which is a calculation of how many people an infected person goes on to infect. Unabated in an unvaccinated population, the R0 of measles is about 12. (Incidentally, this is why measles vaccination is so important.) But something as highly communicable as measles would be undesirable as a deliberate weapon, as it would rage through populations outside the target area as surely as water poured on the top of a hill would flow to the bottom. For biological warfare purposes, you’d typically want a R0 of zero in friendly forces and populations, and a low R0 in the target population is desirable so that the weapon can be targeted effectively. Nobody in their right mind spends time and money engineering a weapon that affects their own population as badly as the target.

Further, when one looks at the characteristics of an “ideal” biological warfare agent and compares this list to the features of this novel coronavirus, there are glaring differences. Covid-19 isn’t the sort of thing one would spend years developing. A biological weapon that disproportionately kills off or incapacitates the elderly and vulnerable, but leaves the economically productive fighting-age population mostly intact seems to be not well-thought through. An incubation period that is both long and variable would have been considered a poor characteristic for biological weapons.

Could these poor characteristics be the result of a half-baked effort? A work in progress that leaked out before it was fine-tuned? No. It really doesn’t work that way, not least of all because of its aforementioned genetic characteristics. This coronavirus is a fully fine-tuned end product, just one that is made by nature, not man. The only “leak” theory that is remotely plausible is that a Chinese lab was studying something that it found in nature, as one would logically do, which then made its way into the wider world through some horrible breach of safety protocols. This allegation has been made, as well, but there’s little information to substantiate this claim at this point. Such an explanation would, in any case, be tragic, not sinister.

Most important, use of a biological weapon is casus belli — clear cause for warfare between nations. Both China and the United States have excellent defensive laboratories well-suited to figuring out if a deliberate biological attack had happened. While the United States and China have economic, political and regional rivalries, they both know that an actual shooting war is not to their benefit and that releasing, even accidentally, a lab-made virus would lead to just that outcome. China starting an actual war, as opposed to a trade war, with the United States makes no sense. The United States, which has not had a biological weapons program since 1970, breaking its own laws to start a war with China makes no sense, either.

This leads to the final question. Who actually benefits from making this coronavirus and deliberately releasing it in China? No one. Acts of chemical and biological warfare in the past have always had an objective, even when done by odd organizations like Aum Shinrikyo in Japan, which was trying to kill middle- and upper-level management at the National Police Agency. How does China or the United States or anyone else actually benefit from the covid-19 pandemic? They don’t. Even if the science gave some hint of man-made origin, none of the practicalities make sense. This is a natural event. Not a man-made plague.

Correction: An earlier version of this piece mistakenly used the term N0 instead of R0.