Chapter 2: Variation Under Nature

Variation Under Nature begins by addressing the inherent difficulty in distinguishing between "species" and "varieties," noting that taxonomic definitions are often arbitrary and rely heavily on the subjective judgment of naturalists rather than fixed biological boundaries. The discussion emphasizes the significance of "individual differences"—the small, heritable variations observed among offspring—as the essential material upon which natural selection acts and accumulates over time. Unlike "monstrosities," which represent sudden and often injurious structural deviations that are rarely preserved in a state of nature, these slight, graduated variations are the true drivers of change. The text explores "protean" or polymorphic genera, where extreme variability makes classification nearly impossible, and notes that dimorphism and trimorphism further complicate the traditional understanding of static species. Through a comparative analysis of various floras and faunas, it is demonstrated that wide-ranging, common, and dominant species are the most prone to developing well-marked varieties. Furthermore, the "manufacturing" of new species appears most active within larger genera; species in these groups often resemble varieties in their close relationships and restricted ranges. Ultimately, the chapter argues that well-defined species are merely strongly marked and permanent varieties—what may be termed "incipient species"—that have emerged through a slow process of divergence and natural selection, rather than through independent acts of creation.