Plain-language answer
The twelve-step method in how to evaluate a coincidence claim is easiest to understand in action. This page walks through all twelve steps applied to a real, already independently fact-checked case on this site — Darwin, Wallace, and the theory that arrived twice — so each step’s abstract instruction can be seen next to a concrete example of what following it actually produces.
The twelve steps, applied
1. Write the exact claim. “In 1858, Charles Darwin and Alfred Russel Wallace, working on opposite sides of the world, independently arrived at the theory of evolution by natural selection within weeks of each other.” A stronger, separate claim also circulates: that Darwin secretly delayed and borrowed from Wallace’s letter.
2. Separate event from interpretation. The event: two naturalists produced similar theories close together in time. The interpretation attached to it varies — “an astonishing, almost inexplicable coincidence” in the popular version, versus “a predictable convergence given a shared scientific moment” in the historical analysis.
3. Verify the facts. The joint 1858 presentation, its date, and the circumstances (neither man present; Darwin grieving his son’s death) are corroborated by the Linnean Society’s own institutional record — a primary, checkable source, not a retelling.
4. Ask when the matching rule was chosen. This is not a post-hoc pattern-match of arbitrary details (like a name or number lining up) — the “match” is two substantively similar scientific theories, which is a meaningful, non-arbitrary similarity rather than a flexible, after-the-fact one.
5. Define a match, precisely. The relevant similarity is: both independently proposed natural selection (differential survival driven by inherited variation) as the mechanism of evolutionary change, arrived at via the same triggering influence.
6. Choose the reference class. Compared with “all pairs of scientists working in the same field, in the same era, with no contact” the coincidence looks larger; compared with “all pairs of naturalists reading the same widely circulated influential book, in the same small, correspondence-linked scientific community” it looks much smaller. This site uses the second, narrower, better-evidenced reference class.
7. Count the opportunities. Sociologist Robert Merton’s research on “multiple discovery” documents that independent, simultaneous scientific discovery is a recurring pattern across the history of science, not a rare anomaly — meaning the pool of “opportunities” for this kind of convergence is larger than intuition suggests.(Merton, 1961)
8. Model the dependencies. Darwin and Wallace were not independent draws from the general population of naturalists: both had read Thomas Malthus’s Essay on the Principle of Population, both did extensive fieldwork observing species variation, and both were embedded in the same small, correspondence-linked circle of Victorian naturalists. These shared influences are exactly the kind of dependency that independence and dependence warns changes the calculation.
9. Estimate the uncertainty. There is no single defensible number for “how likely was this convergence” — the case page reports this qualitatively (a well-documented pattern, not a rare fluke) rather than manufacturing a false-precision probability.
10. Compare explanations. For the independent-discovery half: shared influence and a dense correspondence network, versus true coincidence with no shared cause. The evidence strongly favors shared influence. For the separate priority-dispute claim: a 2012 reconstruction of the mail-steamer timeline supports Darwin’s own account, but a published rebuttal disputes that reconstruction — a live, unresolved historical disagreement.(van Wyhe & Rookmaaker, 2012)
11. Update proportionally. The strength of the independent-discovery evidence (documented shared influences, a well-studied general pattern of multiple discovery) justifies real confidence in that half of the story. The priority-dispute evidence does not currently justify confidence in either direction — the honest position is that professional historians, working from the same primary letters, disagree.
12. State the residual. Established: the independent, near-simultaneous discovery, and that it followed from real, traceable shared influences. Unresolved: whether Darwin’s account of his own conduct in June 1858 is fully accurate. This site takes no position on the second question beyond reporting that the dispute exists.
Why this case, rather than a hypothetical
Using a real, previously fact-checked case rather than an invented example means every step above can be checked against an actual source trail, rather than a convenient illustration built to make the method look clean. The Darwin–Wallace case was chosen because it happens to contain both a well-resolved half (the independent discovery) and a genuinely unresolved half (the priority dispute) — showing that the method’s job is to sort claims into the right bucket, not to resolve every claim into a tidy yes or no.
Related
- Darwin, Wallace, and the theory that arrived twice is the full case page this worked example draws from.
- How to evaluate a coincidence claim is the twelve-step method applied above.
Key takeaways
- Applying the evaluation method to a real case shows that different steps can reach different confidence levels within the very same story — “established” for one part, “unresolved” for another.
- A well-chosen reference class (naturalists sharing an influential book and a correspondence network) explains the Darwin–Wallace convergence without needing an unusual causal story.
- The method’s endpoint is an honest, mixed verdict when the evidence is genuinely mixed — not a forced single conclusion.