Evolution — practice question

California salamanders are terrestrial amphibians. An ancestral population of California salamanders lived in a forest region in northern California. Around 10 million years ago, that original population split, with two groups, A and B, moving away. Population A moved down the California coast on the western side of the Great Central Valley. Population B moved to the east of the Great Central Valley. Today, the two populations are found near one another in southern California. Fig. 8.1 shows the migration routes followed by populations A and B.