The term scientific consensus – as in “there is a scientific consensus on climate change“ – is often used to characterise a matter considered to be scientifically settled.
But the concept of consensus is poorly suited to science, where conclusions must always remain provisional and revisable in the light of new evidence.
The concept of “convergence” better describes the nature of the scientific enterprise. Convergence means we can begin to have confidence that science is accurately/truly describing a phenomenon when the evidence from many and diverse approaches all point to the same explanation. The relative merits of the concepts of consensus and convergence were discussed recently in a recent editorial in Science, and elaborated by Chuck Dinerstein in The American Council for Science and Health.
The value of the convergence concept is illustrated by the history of the MMR vaccine and the claims that this vaccine causes autism. There is a huge amount of evidence from very many lines of investigation that MMR vaccines do not cause autism – in other words, there is extremely strong scientific convergence pointing to this conclusion.
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Nevertheless, US secretary for health Robert Fitzgerald Kennedy jnr does not accept this conclusion, and has asked the Centres for Disease Control and Prevention (CDC) to conduct a new study to demonstrate cases where MMR vaccination does cause autism.
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Given the strength of evidence to date, it seems highly improbable the CDC will demonstrate any link between MMR and autism. Even if it does produce some evidence, the fact remains that innumerable past studies have found no link.
A single contrary indication would not destroy the existing convergence of evidence, which will remain even if a single or a few exceptions come to light. If exceptions do emerge, the onus will be on proponents of the MMR/autism link to explain why scientific convergence so overwhelmingly indicates the opposite conclusion.
And, of course, those who now argue for a link between MMR and autism, in the absence of evidence to date to support their claim, would seize on a single apparent demonstration of a link in some cases as a demonstration that “scientific consensus” is broken, and they would be emboldened to greatly intensify their campaign against vaccination.
In other words, as far as the evidence goes they would have the tail wag the dog and would certainly sow great confusion and persuade many parents not to vaccinate their children, with disastrous consequences.
Creative people who are not completely shackled by existing paradigms are very important when science consistently struggles over a long period to make further progress in explaining a situation
On the other hand, the convergence concept would not lend itself to any such easy manipulation. A single contrary demonstration, albeit interesting and demanding further investigation, would remain a single demonstration to confront innumerable published demonstrations to the contrary.
Another weakness of the consensus concept is that it can be used to bully scientists who dissent from majority opinion. This can be done by refusing monetary support to fund the researches of scientists who question the consensus position. I would imagine that the minority of climate scientists currently seeking support to study potential natural explanations of global warming unrelated to greenhouse gas emissions are finding it very hard to win funding from grant-awarding bodies dominated by scientists hostile to any questioning of the conventional “consensus”.
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Creative people who are not completely shackled by existing paradigms are very important when science consistently struggles over a long period to make further progress in explaining a situation. “Thinking outside the box” may be the only way forward to full explanations in these cases. For example, research on Alzheimer’s disease has heavily concentrated on amyloid plaques for a long time now, but has produced little progress in fully accounting for the disease. The problem calls for creative, not consensus, thinking.
The strong majority position in science can sometimes be wrong and hostile to new opinions. For example, when the idea was first mooted that Earth’s crust is divided into large fragments that “float” on an underlying partly melted layer and that whole continents, once residing close together, gradually moved apart until widely separated (plate tectonics), it was widely resisted by geologists among whom a consensus to the contrary existed.
It took many years for this intercontinental drift and plate tectonics model to become established, as the evidence in its favour gradually accumulated and neatly explained very many observations – in other words, as scientific convergence emerged.
William Reville is an emeritus professor at UCC
