John Hawks On Scientific Consensus

John Hawks, an anthropologist who specializes in archaic hominins, considers at his blog what the term "scientific consensus" means in reaction to an article in the peer reviewed scientific journal Science. He begins as follows:

In an editorial in this week's Science, the journal's editor Holden Thorp develops an argument that the notion of “scientific consensus” has confused public discussion of science. In Thorp's view, the public misunderstands “consensus” as something like the result of an opinion poll. He cites the communication researcher Kathleen Hall Jamieson, who observes that arguments invoking “consensus” are easy for opponents to discredit merely by finding some scientists who disagree.

Thorp notes that what scientists mean by “consensus” is much deeper than a popularity contest. He describes it as “a process in which evidence from independent lines of inquiry leads collectively toward the same conclusion.” Leaning into this idea, Thorp argues that policymakers should stop talking about “scientific consensus” and instead use a different term: “convergence of evidence”.

It would be a big move for a magazine representing the entire breadth of American science to reject the idea of scientific consensus.

For the last twenty years the idea of “scientific consensus” has been widely adopted by scientific organizations and policymakers, especially applied to politically contentious topics such as climate change, vaccine hesitancy, and COVID-19 response. Many organizations shifted their policy advocacy by issuing statements reflecting the consensus of their members. Science itself helped launch this era with the publication of Naomi Oreskes' 2004 article, “The Scientific Consensus on Climate Change”. This article recounted the number of organizations representing scientists that had issued statements or policy documents about the evidence for human-induced climate change.

The purpose of such statements was to counter public perceptions that there might be significant scientific disagreement about climate change.

There use of the term has grown steadily since the late 1960s (image from the linked blog entry):

Another chart in the blog post notes that use of the term "convergence of evidence" peaked in the 1950s and that "scientific consensus" overtook it in frequency of use around 1985.

Hawks argues that there is also a place for the concept of a consilience of evidence:

The idea was formulated by the nineteenth-century philosopher William Whewell, who also coined the word scientist. Whewell wanted to understand how observations give rise to theories. His idea was that the induction of a hypothesis or theory from observations requires another step, a step in which evidence developed by other means of observation must also show consistency with the same theory or hypothesis. He used the term “consilience” for this matching of evidence of different kinds.

Michael Ruse noted Charles Darwin's work as a hallmark of the consilience approach. Darwin brought together evidence from entirely different fields of inquiry: animal and plant breeding, geology, natural history, biogeography, sociology, and many others. He had a remarkable ability to answer questions in one field by examining data in another field entirely. The ability to bring together observations that seem disconnected from each other, explain all of them with one unifying explanation is a powerful mode of scientific thinking.

Consilience of evidence also helps to answer criticism that scientists are closing off debate by excluding ideas that do not fit within their disciplinary boundaries. Where “convergence of evidence” may seem inward-facing, confined to a single research tradition, consilience is explicitly outward-reaching. It requires translation and integration across disciplinary boundaries and sometimes even across different ways of knowing.

I'm skeptical of both the "convergence of evidence" question, which has many of the same problems, and the "consilience of evidence" phrase, which is just beyond the vocabulary of most of the people for whom the rhetoric in which the term might be used is directed.

But the deeper and ultimate question is how to draw the line between what is settled and accepted science, to which any legitimate future challenge has not yet manifested, and scientific ideas which remain the subject of controversy among scientists. 

On one hand, one doesn't really want to adopt the standard of a "hecklers veto" which suggests that a crackpot with weak methodology or methods that cause other scientists inclined to be sympathetic to not take the crackpot seriously, is sufficient to upset a scientific consensus. But on the other hand, one doesn't want to leave the misimpression that scientific truth is a popularity contest or a matter of democratic decision-making, or that the authority and prestige of individual scientists holding a scientific opinion is more important than the evidence and reasoning supporting their opinions. 

When there are two well-reasoned theories advanced by people who are behaving like genuine scientists that are each supported by evidence that doesn't conclusively disprove the alternative, there is no scientific consensus on which one is correct (although there are still many crackpot theories that are definitively rejected by the scientific consensus even at times where there is not a scientific consensus around more than one disputed possible scientific truth to explain the world).

Making these distinctions at a vague, common sense level, in actual real world cases, usually isn't that hard. But putting into words a rule that puts some cases on one side of the line, and other cases on the other side of the line, can be challenging.