Bats are [almost certainly] not closely related to viruses

Disputing the indisputable


Keith S. Taber


Scientific knowledge is provisional

One of the supposed features of scientific knowledge is that it is always, strictly speaking, provisional. Science seeks generalisable, theoretical knowledge – and no matter how strong the case for some general claim may seem, a scientist is supposed to be open-minded, and always willing to consider that their opinion might be changed by new evidence or a new way of looking at things.

Perhaps the strongest illustration of this is Newtonian physics that seemed to work so well for so many decades that for many it seemed unquestionable. Yet we now know that it is not a precise account that always fits nature. (And by 'we know' I mean we know in the sense of having scientific knowledge – we think this, and have very strong grounds to think this, but reserve the right to change our minds in the light of new information!)

Read about the nature of scientific knowledge

When science is presented in the media, this provisional nature of scientific knowledge – with its inbuilt caveat of uncertainty – is often ignored. News reports, and sometimes scientists when being interviewed by journalists, often imply that we now know…for certain… Science documentaries are commonly stitched together with the trope 'and this can only mean' (Taber, 2007) when any scientist worth their salt could offer (even if seemingly less feasible) alternative scenarios that fit the data.

Read about scientific certainty in the media

One might understand this as people charged with communicating science to a general audience seeking to make things as simple and straightforward as possible. However it does reinforce the alternative conception that in science theories are tested allowing them to be straightforwardly dismissed or proved for all time. What is less easy to understand is why scientists seeking to publish work in academic journals to be read by other scientists would claim to know anything for certain – as that is surely likely to seem arrogant and unscientific to editors, reviewers, and those who might read their published work

Science that is indisputable

So, one of two things that immediately made me lack confidence in a published paper about the origin of SARS-CoV-2, the infectious agent considered responsible for the COVID pandemic (Sehgal, 2021), was that the first word was 'Undisputedly'. Assuming the author was not going to follow up with Descartes' famous 'Cogito' ("Undisputedly… I think, therefore I am"), this seemed to be a clear example of something I always advised my own research students to avoid in their writing – a hostage to fortune.


A bold first sentence for this article in a supposedly peer-reviewed research journal

The good scientist learns to use phrases like "this seems to suggest…" rather than "I have therefore proved beyond all possible doubt…"!

To be fair, I came to this paper having already decided that the journal concerned was a predatory journal because it seemed to falsify its Impact Factor, and I had already read a paper in the journal which I felt could not possibly have been subject to peer review by experts in the field. (Was that indisputable? Well, let us say I would find it incredible that expert peer reviewers would not have raised serious concerns about some very obvious errors and omissions in the published paper.)

Prestigious research journals are selective in what they publish – and reject most submissions, or at least require major revisions based on reviewer evaluations. Predatory journals seek to maximise their income from charging authors for publication; and so do not have the concern for quality that traditionally characterised academic publishing. If some of the published output I have seen is a guide, some of these journals would publish virtually anything submitted regardless of quality.

Genetic relatedness of bats and viruses

Now it would be very unfair to dismiss a scientific article based purely on the first word of the abstract. Even if 'undisputedly' is a word that does not sit easily in scientific discourse, I have to acknowledge that writing a scientific paper is in part a rhetorical activity, and authors may sometimes struggle to balance the need to adopt scientific values (such as always being open to the possibility of another interpretation) with the construction of a convincing argument.

Read about research writing

So, I read on.

Well, to the end of the sentence.

"Undisputedly, the horseshoe bats are the nearest known genetic relatives of the Sars-CoV-2 virus."

Sehgal, 2021, p.29 341

Always start a piece of writing with a strong statement

Closest genetic relatives?

Okay, I was done.

I am not a biologist, and so perhaps I am just very ignorant on the topic, but this seemed an incredible claim. Our current understanding of the earth biota is that there has (probably) been descent from a common ancestor of all living things on the planet today. So, just as I am related, even if often only very distantly, to every other cospecific specimen of Homo sapiens on the planet, I am also related by descent from common ancestors (even more distantly) to every chimpanzee, indeed every primate, every mammal, every chordate; indeed every animal; plus all the plants, fungi, protists and monera.

Read 'Intergenerational couplings in the family. A thought experiment about ancestry'

But clearly I share a common ancestor with all humans in the 'brotherhood of man' more recently than all other primates, and that more recently than all other mammals. And when we get to the non-animal kingdoms we are not even kissing cousins.

And viruses – with their RNA based genetics? These are often not even considered to be living entities in their own right.

There is certainly a theory that there was an 'RNA world', a time when some kind of primitive life based on RNA genes existed from which DNA and lifeforms with DNA genomes later evolved, so one can stretch the argument to say I am related to viruses – that if one went back far enough, both viruses and humans (or viruses and horseshoe bats, more to the point of the claim in this article) around today could be considered to be derived from a common ancestor, and that this is reflected in patterns that can be found in their genomes today.

The nearest genetic relative to SARS-CoV-2 virus?

The genome of a virus is not going to be especially similar to the genome of a mammal. The SARS-CoV-2 virus is a single stranded RNA virus which will be much more genetically similar to other such viruses that to organisms with double stranded DNA. It is famously a coronavirus – so surely it is most likely to be strongly related to other coronaviruses? It is called 'SARS-CoV-2' because of its similarity to the virus that causes SARS (severe acute respiratory syndrome): SARS-CoV. These seems strong clues.

And the nearest genetic relative to horseshoe bats are…

And bats are mammals. The nearest relatives to any specific horseshoe bat are other bats of that species. And if we focus at the species level, and ask what other species would comprise the nearest genetic relatives to a species of horseshoe bats? I am not an expert, but I would have guessed other species of horseshoe bat (there are over a hundred such species). Beyond that family – well I imagine other species of bat. Looking on the web, it seems that Old World leaf-nosed bats (and not viruses) have been mooted from genetic studies (Amador, Moyers Arévalo, Almeida, Catalano & Giannini, 2018) as the nearest genetic relatives of the horsehoe bats.


Annotated copy of Figure 7 from Amador et al., 2018

So, although I am not an expert, and I am prepared to be corrected by someone who is, I am pretty sure the nearest relative that is not a bat would be another mammal – not a bird, not a fish, certainly not a mollusc or insect. Mushrooms and ferns are right out of contention. And, no, not a virus. 1

Judge me on what I mean to say – not what I say

Perhaps I am being picky here. A little reflection suggests that surely Sehgal (in stating that "the horseshoe bats are the nearest known genetic relatives of the Sars-CoV-2 virus") did not actually mean to imply that "the horseshoe bats are the nearest known genetic relatives of the Sars-CoV-2 virus", but rather perhaps something along the lines that an RNA virus known to infect horseshoe bats was the nearest known genetic relative of the Sars-CoV-2 virus.

Perhaps I should have read "the horseshoe bats are the nearest known genetic relatives of the Sars-CoV-2 virus" as "the horseshoe bats are hosts to the nearest known genetic relatives of the Sars-CoV-2 virus"? If I had read on, I would have found reference to a "bat virus RaTG13 having a genome resembling the extent of 98.7% to that of the Sars-CoV-2 virus" (p.29 341).

Yet if a research paper, that has supposedly been subject to rigorous peer review, manages to both misrepresent the nature of science AND make an obviously factually incorrect claim in its very first sentence, then I think I can be forgiven for suspecting it may not be the most trustworthy source of information.


Work cited
  • Amador, L. I., Moyers Arévalo, R. L., Almeida, F. C., Catalano, S. A., & Giannini, N. P. (2018). Bat Systematics in the Light of Unconstrained Analyses of a Comprehensive Molecular Supermatrix. Journal of Mammalian Evolution, 25(1), 37-70. https://doi.org/10.1007/s10914-016-9363-8
  • Sehgal, M.L. (2021) Origin of SARS-CoV-2: Two Schools of Thought, Biomedical Journal of Scientific & Technical Research, July, 2020, Volume 37, 2, pp 29341-29356
  • Taber, K. S. (2007) Documentaries can only mean one thingPhysics Education, 42 (1), pp.6-7

Note:

1 It is perfectly possible logically for organism Y (say a horseshoe bat) to be the closest genetic relative of organism X (say a coronavirus) without organism X being the closest genetic relative of organism Y. (By analogy, someone's closest living genetic relative could be a grandchild whose closest genetic relative is their own child or their parent that was not a child of that grandparent.) However, the point here is that bat is not even quite closely related to the virus.

 

Author: Keith

Former school and college science teacher, teacher educator, research supervisor, and research methods lecturer. Emeritus Professor of Science Education at the University of Cambridge.

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