Discovering a ring species
Of course, since this all would have happened millions of years ago, Robert wasn't around to observe any of it. He based his ideas on the morphology, or body form, of the subspecies in this case, their color patterns. First, neighboring subspecies were more similar to one another than to those across the ring and seemed to blend into one another. From this, he hypothesized that Ensatina represented a ring species. Robert also noticed that the northern coastal form, called picta, had a pattern of colors that seemed to encompass the other subspecies. It was easy to imagine how the more specialized southern forms could have evolved from picta. Based on this, Robert hypothesized that the two southward-moving Ensatina lineages had both emerged from picta's immediate ancestors.
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1Stebbins, R.C. 1949. Speciation in salamanders of the plethodontid genus Ensatina. University of California Publications in Zoology 48:377-526.
Robert Stebbins photo courtesy of the Museum of Vertebrate Zoology Archives; subspecies range map, Ensatina photos, and the photo of Ensatina eschscholtzii picta provided by Tom Devitt
Understanding Evolution © 2016 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California