Where does cline collide?

In evolutionary biology, a cline is a gradient in a measurable character across the geographic range of a species, so that body size, colour, or allele frequency shifts gradually from one end of the range to the other rather than in sharp jumps. Huxley's 1938 Clines: An Auxiliary Taxonomic Principle coined the term precisely to describe these continuous gradients, which cut across the discrete subspecies that taxonomists had been drawing. The referent is a spatial gradient in a biological trait, driven by gradual change in selection or gene flow, and it is a different thing from a continuum of grammatical forms despite the shared idea of a smooth gradation.[1]

Unit

The rate of change of a trait or allele frequency across geographic distance

Recovery means

Not applicable

Measured by

Measured by regressing a trait or allele frequency against geographic position and estimating the slope and width of the gradient

In linguistics, a cline is a continuum along which a form shifts gradually in status, classically the grammaticalization cline, where a full lexical word drifts step by step into a grammatical marker, passing through intermediate stages rather than changing all at once. Hopper and Traugott's Grammaticalization uses the cline to capture how, for example, a verb meaning 'to go' becomes a future-tense marker through a chain of small, directional reanalyses. The referent is a graded continuum of linguistic forms over time, charted by intermediate stages, and it is unrelated to a geographic gradient in an organism's traits beyond the shared notion of smooth gradation.[2]

Unit

The ordered sequence of intermediate stages along a form's continuum

Recovery means

Not applicable

Measured by

Traced through historical and comparative evidence placing forms at successive, directional stages along the continuum