Butterfly or Bat

The coronavirus started when a person ate a bat or another wild animal infected by a bat – both being in the same neighborhood market where wild animals were sold.  This person became “patient zero” in what has blossomed into the coronavirus pandemic.

Of course, the bat cannot be faulted.  The behaviors of the human involved were the cause.  Actually, many people exhibited these behaviors, but someone had to be patient zero.  We can argue that, in effect, someone was randomly selected.

Cheng and colleagues (2007) predicted this, concluding, “The presence of a large reservoir of SARS-CoV-like viruses in horseshoe bats, together with the culture of eating exotic animals in southern China, is a time bomb.”  Twelve years later, the fuse for the time bomb was lit and it has now exploded.

This phenomenon got me thinking about Edward Lorenz’s “butterfly effect,” whereby a small change in the initial conditions of a deterministic nonlinear system can result in large differences in later states of that system (Lorenz, 1963). Focused on predicting the weather, Lorenz posited that the exact time of formation and the exact path taken by a tornado could be influenced by minor perturbations such as the flapping of the wings of a distant butterfly several weeks earlier.

Lorenz discovered the effect when he observed that runs of his weather model where very small changes in initial conditions created significantly different outcomes.  Henri Poincaré and Norbert Wiener had earlier made similar observations.  Their conclusion was that deterministic chaos was possible for nonlinear systems.

However, the overall system was not really deterministic.  The butterfly represented small random variations of initial conditions.  So, the butterfly was part of the system, just as the bat was part of the coronavirus system.

But the system associated with coronavirus is much larger.  It includes human behaviors at a population level.  These population behaviors set the stage for patient zero.”

Patton (2020) reports that “changes to human behavior — the destruction of natural habitats, coupled with huge numbers of people traveling around the globe — has enabled diseases that were once locked away in nature to cross into people fast.” He notes, “bats are the only mammal that can fly, allowing them to spread in large numbers over wide areas.”

Bats are the second most common mammals after rodents. There are roughly 1,000 species of bats.  They are perhaps 20% of the overall mammal population. Humans represent roughly 0.1% of mammals.  Thus, there are 200 bats for each human. This benefits humans.  Bats eat lots of insects. Some disperse seeds and pollinate flowers.

However, as we destroy their natural habitats, they tend to get stressed.  Patton reports “This stress challenges their immune system and they find it harder to cope with pathogens they otherwise took in stride.”  And, then we eat them and somebody gets to be patient zero.


Cheng, V.C.C., et al. (2007). Severe acute respiratory syndrome coronavirus as an agent of emerging and reemerging infection. Clinical Microbiology Reviews, 20 (4), 660-694.

Lorenz, Edward N. (March 1963). Deterministic nonperiodic flow. Journal of the Atmospheric Sciences. 20 (2): 130–141.

Patton, N. (2020). Bats are not to blame for coronavirus. Humans are. CNN, March 20, 7:30AM.

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