What is multiple lines of evidence?

Multiple lines of evidence is a concept in personal epistemology: Ideas supported by multiple independent lines of evidence are more reliable.

Example: Continental drift was proposed by Alfred Wegener in 1912, but for decades the geological establishment dismissed it — largely because Wegener could not explain the mechanism by which continents moved. He had one line of evidence: the shapes of the continents fit together like puzzle pieces. That alone was not compelling. Then, over the following decades, independent lines of evidence accumulated. Paleontologists found identical fossil species on continents separated by thousands of miles of ocean. Geophysicists discovered matching magnetic stripe patterns on either side of mid-ocean ridges. Seismologists mapped earthquake epicenters and found they traced narrow, continuous bands that outlined the edges of moving plates. Geologists found identical rock formations and mineral deposits on coastlines that had once been joined. No single line of evidence was conclusive. But when five independent disciplines — each using different methods, different instruments, different assumptions — all converged on the same conclusion, the theory of plate tectonics became one of the most robust in all of science. The supporting relationships between those lines of evidence did not merely add up. They multiplied. Each new independent source of support made the conclusion not incrementally more likely, but dramatically more certain.

This concept is part of Phase 13 (Relationship Mapping) in the How to Think curriculum, which builds the epistemic infrastructure for relationship mapping.