How a geographic barrier created a living evolutionary loop

Nature · Published 30 September 2026 Swipe more like this →

In short: Across the Western coast, a single species of salamander is slowly drifting apart. By traveling around a massive dry valley, these colorful creatures have formed a rare biological phenomenon known as a ring species, providing a real-time window into how new species are born.

The ensatina salamander group, stretching from Canada down to Baja California, presents a fascinating biological puzzle. While these salamanders exhibit diverse survival strategies—ranging from striking warning colors to deceptive camouflage—they are still classified as a single species. This classification holds because neighboring populations can successfully mate and produce healthy offspring as they move along the coast.

However, a profound shift is occurring at the southern edges of their territory. When the Monterey ensatina meets the large-blotched ensatina, the two lineages rarely produce offspring, even where their ranges overlap. This separation is driven by a complex interplay of behavioral differences, habitat preferences, and genetic divergence. This phenomenon makes them a classic example of a 'ring species.'

A ring species occurs when a population expands around a geographic barrier—in this instance, California’s arid Central Valley—only to reunite with its ancestral lineage millions of years later as nearly distinct entities. This structure offers scientists a rare, observable snapshot of the evolutionary process. By studying how these populations are currently diverging, researchers can build upon the foundational theories of speciation first proposed by Charles Darwin in his 1859 work, 'On the Origin of Species.'

Beyond their evolutionary significance, these amphibians possess unique chemical defenses. They can release a milky, slightly toxic substance from glands located in their tails. While this secretion serves as a deterrent, it is not considered dangerous to the predators that encounter them.

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