Fallacy?

Just-so story

A plausible story of how something came about is offered as the explanation, without independent tests.

Also called: Untested narrative · Adaptive storytelling

The test

Does the story make a prediction that could fail? Has anyone checked it?

The name comes from Rudyard Kipling's Just So Stories (1902), such as “How the Leopard Got His Spots.” Stephen Jay Gould and Richard Lewontin used it in 1979 to criticise their own field: evolutionary biologists, they argued, too readily explained every trait with an adaptive story, and too rarely tested the stories.

Historical sciences must reconstruct the past, and reconstruction needs narrative. The question is whether the narrative is treated as a hypothesis, with consequences that could fail, or as a finished explanation.

Seen on both sides

In mainstream arguments
It would be a just-so story to explain the origin of a structure by a sequence of advantageous steps that is plausible, but untested and perhaps untestable.
In critical arguments
It would be a just-so story to explain a particular rock formation by a flood scenario, without testing the specific predictions that the scenario makes for that formation.
Not a fallacy when

The scenario is put forward as a hypothesis, and its specific predictions are then tested.

Diagnosed on this site

  • Claim № 2.01 · Transitional seriesPossible
    In the claim as taught

    Arranging fossils as ancestor and descendant tells a story about them. Henry Gee's point is that the story, as a line of descent, is not itself a testable hypothesis.

Further reading

  1. Gould SJ, Lewontin RC. “The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme.” Proc. R. Soc. Lond. B 205:581–598 (1979).