Alfred Russel Wallace and the Darwinian Species Concept: His Paper on the Swallowtail Butterflies (Papilionidae) of 1865

Abstract

Soon after his return from the Malay Archipelago, Alfred Russel Wallace published one of his most significant papers. The paper used butterflies of the family Papilionidae as a model system for testing evolutionary hypotheses, and included a revision of the Papilionidae of the region, as well as the description of some 20 new species. Wallace argued that the Papilionidae were the most advanced butterflies, against some of his colleagues such as Bates and Trimen who had claimed that the Nymphalidae were more advanced because of their possession of vestigial forelegs. In a very important section, Wallace laid out what is perhaps the clearest Darwinist definition of the differences between species, geographic subspecies, and local 'varieties.' He also discussed the relationship of these taxonomic categories to what is now termed 'reproductive isolation.' While accepting reproductive isolation as a cause of species, he rejected it as a definition. Instead, species were recognized as forms that overlap spatially and lack intermediates. However, this morphological distinctness argument breaks down for discrete polymorphisms, and Wallace clearly emphasised the conspecificity of non-mimetic males and female Batesian mimetic morphs in Papilio polytes, and also in P. memnon, on the grounds of reproductive continuity. Finally, Wallace detailed how natural selection explains various forms of parallel evolution, including mimicry.Keywords: History of evolution, mimicry, species concepts, geographic variation, taxonomic inflation, island biology, Lepidoptera. RESUMENPoco después de su retorno del archipiélago Malayo, Alfred Russel Wallace publicó uno de sus trabajos más relevante. En éste usaba mariposas de la familia Papilionidae como modelos para poner a prueba hipótesis evolutivas, e incluía una revisión de los Papilionidae de la región y la descripción de 20 nuevas especies. Wallace argumentó que los Papilionidae representaban las mariposas más avanzadas, opinión contraria a la sostenida por sus colegas, incluyendo Bates y Trimen, quienes pensaban que los Nymphalidae eran más avanzados debido a su posesión de patas vestigiales. En una sección muy importante, Wallace formuló lo que quizás constituye la más clara definición darwiniana de las diferencias entre especies, subespecies geográficas y "variedades" locales. También discutió la relación de estas categorías taxonómicas con lo que hoy se denomina "aislamiento reproductivo". Mientras aceptaba el aislamiento reproductivo como una de las causas del origen de especies, lo rechazó como una definición de especie. Por el contrario, las especies se reconocían como formas que se sobreponen espacialmente y carecen de intermedios. Sin embargo, este argumento basado en distinción morfológica falla ante la presencia de polimorfismos discretos. No obstante, basándose en continuidad reproductiva, Wallace claramente enfatizó la conespecificidad en Papilio polytes de machos no miméticos, hembras

Why was Darwin’s view of species rejected by twentieth century biologists?

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Ecotypes and the controversy over stages in the formation of new species

“…Not long after Darwin's publication of ‘The Origin of Species’, Wallace (1865) laid out a classification scheme for distinct stages in the formation of species based on observations of swallowtail butterflies. Mallet has recently suggested that this may have been ‘the first attempt by a Darwinist to enumerate and classify the … “varieties” that Darwin argued were the forerunners of species’ (Mallet, 2009: 40). Darwin, Wallace, and their followers thus represented the first wave of interest in understanding the stages of the speciation process.…”

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Deciphering the evolution of birdwing butterflies 150 years after Alfred Russel Wallace

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