The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution

by Richard Dawkins

If you go up to the mountains that bound the north end of the Central Valley, which up there is called the Sacramento Valley, you’ll find only one species of Ensatina. Its appearance is intermediate between the blotched and the plain species: mostly brown, with rather indistinct blotches. It is not a hybrid between the two: that is the wrong way to look at it. To discover the right way, make two expeditions south, sampling the salamander populations as they fork to west and east on either side of the Central Valley. On the east side, they become progressively more blotched until they reach the extreme of klauberi in the far south. On the west side, the salamanders become progressively more like the plain eschscholtzii that we met in the zone of overlap at Camp Wolahi. This is why it is hard to treat Ensatina eschscholtzii and Ensatina klauberi with confidence as separate species. They constitute a ‘ring species’ (see plate 21). You’ll recognise them as separate species if you only sample in the south. Move north, however, and they gradually turn into each other.