Johnson, Kurt, and Blackwell, Stephen H. DNA, Nabokov, and Biogeography. 2024

The authors examine the prehistory of Nabokov’s surprising, controversial, and ultimately vindicated 1945 scenario for the dispersal of Polyommatini Blue butterflies across the Americas. This scenario produced one of the more poetic passages in Nabokov’s scientific writings, referring to the “Wellsian time machine” a researcher might straddle to watch the various migrations of butterfly groups from Eurasia, across Beringia, to North and then South America. Due to their morphological peculiarities, Nabokov proposed that the butterfly groups came not in a single wave, later spreading and diversifying across the Americas from North to South, but rather in distinct waves that left the impression that modern North American species arrived more recently than those currently found in South America. The scenario could not be tested in Nabokov’s time, but it gave rise to the well-known DNA-based study (Vila et al.), published in 2011, proving that Nabokov’s proposal was exactly correct, and on that basis advancing a novel theory of thermal filtration across Beringia, utilizing genetic markers indicating ancient climate tolerances in different lineages. The present article asks a question that was passed over by Vila et al.: how did Nabokov arrive at his hypothesis—by luck, or by specific reliance on the data at hand? Piecing together phrases from two widely-separated articles, one on taxa from North America and the other on taxa from South America, the authors demonstrate the analytical method Nabokov used to derive his conclusion, which turns out to be factually derived from his transformation series illustrating the evolution of genitalic morphology. This transformation series allowed him to posit an “ancestral type” or “aspect” of the genera he worked on, and from this conclusion, he derived his surprisingly accurate dispersal scenario. These details of Nabokov’s analytical process further anchor his legacy as a pioneer phylogenetic systematist.