Because the emergence of new viruses (and pandemics) is a matter of statistics

When we observe something that deviates greatly from the average of what we are used to experiencing, we immediately become suspicious. If it is about things of lesser importance, after having investigated for some time, we file as a curiosity what has attracted our attention, even without having found a particular explanation that justifies the anomaly. However, when the anomalous event we experience is particularly relevant to us, we try at all costs to develop theories that justify it causally, often invoking a deliberate will to “explain” the observation made. This is the root of the theories that, for example, want at all costs to justify the birth of an epidemic as a phenomenon of human origin, rather than natural.. Without prejudice to the most bizarre theories, the possibility of a laboratory accident is always real; however, a series of natural events are equally possible which, in retrospect, appear more probable.

The simple emergence of a pathogen that is “too” problematic compared to what we are used to, that is, which deviates too much from the average of what we are used to considering, leads to the rejection of any possibility that this can happen naturally, as much as regards the origin of an epidemic such as that of SARS-CoV-2, both as regards its persistence for years with many consecutive waves (an anomaly must end soon, it is imagined), and finally as regards the possibility that new variants are worse than the previous ones, and therefore continue to constitute a greater danger than we are used to. It is always the same example: we are not used to dealing with deviations from the statistical mean of what we have observed in our lives and perhaps in those of our parents, and the more a phenomenon deviates from that average, the more it seems to us that it could not have occurred by chance.

We are strongly inclined to imagine the natural world as relatively stable, with fluctuations falling within the range we have always observed: this explains why it is so difficult to prepare for exceptional events, and also why a pathogen can appear dramatically more dangerous to us when it strikes us. close, compared to when it does in those countries where “normally” there are more dangerous epidemics: do you remember the beginning of the pandemic and the illusion that it was a problem in China? It would be good for everyone, beyond their specific competence, to consider the following: anomalies, deviations from the average of what we usually observe, are not only possible, but inevitable, in those phenomena that obey the laws of statistics.

An unlikely event is a possible event, which has the only characteristic of occurring fewer times, given a sufficient number of repetitions of the circumstances from which it could arise; the time in which it will take place, starting from a chosen instant, depends on the number of times in which those circumstances are repeated. Now, for pathogens in general, and for viruses in particular, we have literally trillions of replicas in a year made by a number of viruses altogether greater than the stars in our universe; taken as a whole, therefore, the phenomenon of viral replication represents one of the natural events in which one has the highest number of repetitions per unit of time.

Considering that every single replication event produces a new virus mutated more or less extensively compared to its progenitor in a non-negligible percentage of cases, it is evident that, even if only looking at the few hundred types of viruses known to be able to infect us, the probability that new “catastrophic” types emerge as happened for SARS-CoV-2 are far from negligible. The fact that these are rare events depends first of all on our immune system, then on the circumstances that can limit the spread to a few individuals; but if these rare events did not occur, then yes we should be suspicious. Each “average” of events of a certain type provides for a probability distribution, which means that events extremely distant from the average, albeit with low probability, are always contemplated; and if the “roll of the dice”, as in the case of the generation of new viruses, are an immense number, even very anomalous events will take place in not excessively long times.

Here: a simple statistical argument should make one reason that, with viruses, the extreme deviations that will occur are less infrequent than one might expect.. More generally, it should lead us to consider that, in our life, we will be able to observe great oddities, and beyond those to which we will pay attention, before constructing ad hoc hypotheses to explain the anomaly, perhaps we should ask ourselves if we are not simply observing the waiting queue for some probability distribution. In fact, whatever has at its base a mechanism that guarantees its possibility, will end up occurring, if at the base there is an infinite repetition of the conditions that trigger that mechanism; we will not see donkeys flying, therefore, but we will certainly be able to see dangerous viruses suddenly disappear and apparently re-emerge from nowhere.