Land snails as a model to understand the role of history and selection in the origins of biodiversity

It is nearly 100 years since the first studies on variation in the shell patterns of land snails. Subsequently, snails have come to play an important role in our understanding of natural selection in the wild. In particular, snails have been an ideal model to understand the roles of history and selection in the origins of diversity. More recently, many studies have investigated the molecular genetic variation within snails. It is clear that snails are unusual, because some genes may vary by 10%-30% within a species. This molecular variation affords an excellent opportunity to further understand the action of natural selection in shaping the present-day phenotypic diversity. In the first part of this review, I illustrate the distinction between the historical and selective interpretations using one of the best-studied species, Cepaea nemoralis, and the example of "area effects." In the second part, studies that have compared patterns of morphological and molecular variation (especially DNA) are examined.