Gulick, JT

…However, it was M. Wagner (1868) who proposed the theory of separations, which states that isolation is not only a secondary role in the sense that natural selection is at work due to different factors in different geographical populations, but that isolation itself is a necessary condition for species differentiation. J. T. Gulick (1872) also collected and studied land snails from the Hawaiian archipelago, and found that there was a great deal of variation in the shape, color, and markings of the shells, and that the types differed from valley to valley, while nearby valleys were similar to each other, and the differences became greater the further away they were, and he argued that geographical isolation was important in the differentiation of species and genera. G. J. Romanes (1848-94) also placed importance on isolation as well as mutation and heredity, and from the standpoint of what is now called reproductive isolation, he argued that differences in the structure of reproductive organs and the timing of reproduction were important causes of species differentiation. …

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Source | Heibonsha World Encyclopedia 2nd Edition | Information

…しかし隔離は地理的に異なった集団には異なった要因による自然淘汰が働くという意味での副次的な役割をもつにとどまらず，隔離こそが種分化の必要条件だとする隔離説Separationstheorieを唱えたのはワーグナーM.Wagner(1868)であった。ギューリックJ.T.Gülick(1872)もハワイ群島の陸産巻貝を集めて研究し，貝の形，色，斑紋について変異が多く，谷ごとに種類が異なり，近くの谷は互いに似ており，遠くなるにつれ違いも大きくなることを明らかにし，種，属の分化に地理的な隔離が重要であると主張した。ローマニズG.J.Romanes(1848‐94)も変異，遺伝とともに隔離を重視し，今日いうところの生殖的隔離の立場から生殖器官の構造，生殖時期の相違が種の分化の重要な原因であると主張した。…

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