The short answer is almost certainly yes, at least in part. The closest known relatives of SARS-CoV-2, the virus that causes COVID-19, all come from horseshoe bats. A bat coronavirus called RaTG13 shares 96.2% of its genome with SARS-CoV-2, making it the nearest known relative. What remains unresolved is exactly how the virus got from bats to people, whether it jumped directly or passed through another animal first, and whether that jump happened in the wild or possibly in a laboratory setting.
The Genetic Link to Horseshoe Bats
Coronaviruses closely related to SARS-CoV-2 have been found in at least four species of horseshoe bats (genus Rhinolophus) across China and Southeast Asia. The closest match, RaTG13, was isolated from a horseshoe bat collected in Yunnan province, China, in 2013. Its genome is 96% identical to SARS-CoV-2, and the proteins shared between the two viruses are more than 95% identical. Another relative, RmYN02, was found in a different horseshoe bat species sampled in Yunnan in 2019. Still others turned up in bats from Thailand and Cambodia, collected as far back as 2010.
A 96% match sounds nearly identical, but in viral evolution that gap represents decades of divergence. The virus would have needed years of circulating and mutating, likely in bats and possibly in other animals, before it could efficiently infect human cells. Researchers studying the mutation patterns of SARS-CoV-2 found that they closely resemble the mutation patterns of bat coronaviruses, suggesting the virus spent significant time evolving in bat cells or something very similar before making the jump to people.
How a Bat Virus Could Infect Humans
For a coronavirus to jump from bats to humans, its spike protein, the molecular key it uses to unlock and enter cells, needs to fit a receptor on human cells called ACE2. Bat coronaviruses are optimized for bat ACE2, which differs from the human version. The virus would need mutations in its spike protein to bind effectively to human ACE2, and this adaptation could happen gradually in bat populations, rapidly in an intermediate animal host, or some combination of both.
Structural studies comparing SARS-CoV-2 with a related bat virus called BANAL-52 illustrate this clearly. BANAL-52’s spike protein fits neatly with bat ACE2 but poorly with human ACE2. SARS-CoV-2’s spike protein, by contrast, binds human ACE2 with high affinity. The specific amino acids responsible for this preference have been mapped, and they follow the same structural principles seen in other coronaviruses that have adapted to new hosts. In other words, the adaptation looks like a natural evolutionary process, not something fundamentally different from what scientists have seen before.
The Missing Intermediate Host
When SARS (the original, from 2003) emerged, scientists traced it from bats through civets to humans relatively quickly. For COVID-19, the intermediate host, if one exists, has never been confirmed. Several candidates have been proposed: pangolins, raccoon dogs, civets, rodents, minks, and even snakes. Pangolins got early attention because viruses found in them share up to 92.4% of their genome with SARS-CoV-2. Rodents are another strong candidate. Researchers found that fragments of the SARS-CoV-2 spike protein exactly match peptide sequences found in mice and rats, and the phylogenetic analysis of the spike protein points to rodents as a plausible intermediate reservoir.
Genetic sampling at the Huanan Seafood Market in Wuhan, where many early COVID-19 cases clustered, added an intriguing piece to the puzzle. Every environmental sample that tested positive for SARS-CoV-2 at one particular stall also contained DNA from wildlife species, including civets, bamboo rats, and raccoon dogs. Researchers detected animal viruses that specifically infect raccoon dogs, civets, and bamboo rats in those same samples. This doesn’t prove these animals carried SARS-CoV-2, but it places susceptible species and the virus in the same location at the same time.
Why Bats Carry So Many Coronaviruses
Bats are not just the suspected source of COVID-19. They are the primary natural reservoir for the entire family of SARS-related coronaviruses, as well as the likely origin of MERS, Ebola, Nipah, and other viruses that have spilled into human populations. Several features of bat biology make this possible. Bats are the second most diverse group of mammals on Earth, with over 1,400 species, and many roost in dense colonies numbering in the thousands or millions. These crowded roosts create ideal conditions for viruses to circulate, mutate, and jump between bat species.
Coronavirus shedding in bats follows seasonal patterns, peaking during summer or autumn in Asia and during dry seasons in parts of Africa, likely tied to breeding cycles, food availability, and stress. The sheer diversity of horseshoe bats across southern China and Southeast Asia means an enormous pool of coronaviruses is constantly evolving in these populations. In China alone, SARS-related coronaviruses have been detected in at least five horseshoe bat species beyond the four that carry the closest SARS-CoV-2 relatives.
The Lab Leak Question
The alternative hypothesis is that SARS-CoV-2 escaped from a research laboratory, most likely the Wuhan Institute of Virology, which is located in the same city where the pandemic began and was actively studying bat coronaviruses. This idea is not fringe science. WHO’s Scientific Advisory Group for the Origins of Novel Pathogens (SAGO) stated in its June 2025 report that “all hypotheses must remain on the table, including zoonotic spillover and lab leak.”
That said, the same report concluded that “the weight of available evidence suggests zoonotic spillover, either directly from bats or through an intermediate host.” The scientific case for a natural origin rests on the genetic evidence linking the virus to bat coronaviruses, the presence of susceptible wildlife at the Huanan market, the mutation patterns consistent with bat-cell evolution, and the precedent set by SARS and other zoonotic outbreaks. The case for a lab leak rests largely on circumstantial factors: the proximity of the Wuhan lab, the type of research conducted there, and the absence of a confirmed animal source.
A major obstacle to resolving the question is that China has not shared key data. WHO has requested genetic sequences from early COVID-19 patients, detailed records of animals sold at Wuhan markets, and information about biosafety conditions and research activities at Wuhan laboratories. As of mid-2025, none of this has been provided.
What We Know and What’s Still Missing
The genetic evidence strongly supports bats as the original source of SARS-CoV-2. The virus’s closest known relatives all come from horseshoe bats, its spike protein shows structural hallmarks of natural adaptation from bat to human receptors, and its mutation signature matches what you’d expect from long evolution in bat cells. These findings have been replicated across multiple independent research groups using different methods.
What’s missing is the direct link: the bat population or intermediate animal carrying a virus close enough to SARS-CoV-2 to represent the immediate precursor. Until that animal is found, or until laboratory records are opened for independent review, the precise pathway from bats to the first human infection will remain a matter of strong evidence pointing in one direction but not yet a closed case.