Darwin and Modern Science [222]
of the effect of the geological changes upon the dispersal of animals did after all advance the problem but little.
Hitherto the marine faunas had been neglected. This was remedied by E. Forbes, who established nine homozoic zones, based mainly on the study of the mollusca, the determining factors being to a great extent the isotherms of the sea, whilst the 25 provinces were given by the configuration of the land. He was followed by J.D. Dana, who, taking principally the Crustacea as a basis, and as leading factors the mean temperatures of the coldest and of the warmest months, established five latitudinal zones. By using these as divisors into an American, Afro-European, Oriental, Arctic and Antarctic realm, most of which were limited by an eastern and western land-boundary, he arrived at about threescore provinces.
In 1853 appeared L.K. Schmarda's ("Die geographische Verbreitung der Thiere", Wien, 1853.) two volumes, embracing the whole subject. Various centres of creation being, according to him, still traceable, he formed the hypothesis that these centres were originally islands, which later became enlarged and joined together to form the great continents, so that the original faunas could overlap and mix whilst still remaining pure at their respective centres. After devoting many chapters to the possible physical causes and modes of dispersal, he divided the land into 21 realms which he shortly characterises, e.g. Australia as the only country inhabited by marsupials, monotremes and meliphagous birds. Ten main marine divisions were diagnosed in a similar way. Although some of these realms were not badly selected from the point of view of being applicable to more than one class of animals, they were obviously too numerous for general purposes, and this drawback was overcome, in 1857, by P.L. Sclater. ("On the general Geographical Distribution of the members of the class Aves", "Proc. Linn. Soc." (Zoology II. 1858, pages 130-145.) Starting with the idea, that "each species must have been created within and over the geographical area, which it now occupies," he concluded "that the most natural primary ontological divisions of the Earth's surface" were those six regions, which since their adoption by Wallace in his epoch-making work, have become classical. Broadly speaking, these six regions are equivalent to the great masses of land; they are convenient terms for geographical facts, especially since the Palaearctic region expresses the unity of Europe with the bulk of Asia. Sclater further brigaded the regions of the Old World as Palaeogaea and the two Americas as Neogaea, a fundamental mistake, justifiable to a certain extent only since he based his regions mainly upon the present distribution of the Passerine birds.
Unfortunately these six regions are not of equal value. The Indian countries and the Ethiopian region (Africa south of the Sahara) are obviously nothing but the tropical, southern continuations or appendages of one greater complex. Further, the great eastern mass of land is so intimately connected with North America that this continent has much more in common with Europe and Asia than with South America. Therefore, instead of dividing the world longitudinally as Sclater had done, Huxley, in 1868 ("On the classification and distribution of the Alectoromorphae and Heteromorphae", "Proc. Zool. Soc." 1868, page 294.), gave weighty reasons for dividing it transversely. Accordingly he established two primary divisions, Arctogaea or the North world in a wider sense, comprising Sclater's Indian, African, Palaearctic and Neartic regions; and Notogaea, the Southern world, which he divided into (1) Austro-Columbia (an unfortunate substitute for the neotropical region), (2) Australasia, and (3) New Zealand, the number of big regions thus being reduced to three but for the separation of New Zealand upon rather negative characters. Sclater was the first to accept these four great regions and showed, in 1874 ("The geographical distribution of Mammals", "Manchester Science Lectures", 1874.), that
Hitherto the marine faunas had been neglected. This was remedied by E. Forbes, who established nine homozoic zones, based mainly on the study of the mollusca, the determining factors being to a great extent the isotherms of the sea, whilst the 25 provinces were given by the configuration of the land. He was followed by J.D. Dana, who, taking principally the Crustacea as a basis, and as leading factors the mean temperatures of the coldest and of the warmest months, established five latitudinal zones. By using these as divisors into an American, Afro-European, Oriental, Arctic and Antarctic realm, most of which were limited by an eastern and western land-boundary, he arrived at about threescore provinces.
In 1853 appeared L.K. Schmarda's ("Die geographische Verbreitung der Thiere", Wien, 1853.) two volumes, embracing the whole subject. Various centres of creation being, according to him, still traceable, he formed the hypothesis that these centres were originally islands, which later became enlarged and joined together to form the great continents, so that the original faunas could overlap and mix whilst still remaining pure at their respective centres. After devoting many chapters to the possible physical causes and modes of dispersal, he divided the land into 21 realms which he shortly characterises, e.g. Australia as the only country inhabited by marsupials, monotremes and meliphagous birds. Ten main marine divisions were diagnosed in a similar way. Although some of these realms were not badly selected from the point of view of being applicable to more than one class of animals, they were obviously too numerous for general purposes, and this drawback was overcome, in 1857, by P.L. Sclater. ("On the general Geographical Distribution of the members of the class Aves", "Proc. Linn. Soc." (Zoology II. 1858, pages 130-145.) Starting with the idea, that "each species must have been created within and over the geographical area, which it now occupies," he concluded "that the most natural primary ontological divisions of the Earth's surface" were those six regions, which since their adoption by Wallace in his epoch-making work, have become classical. Broadly speaking, these six regions are equivalent to the great masses of land; they are convenient terms for geographical facts, especially since the Palaearctic region expresses the unity of Europe with the bulk of Asia. Sclater further brigaded the regions of the Old World as Palaeogaea and the two Americas as Neogaea, a fundamental mistake, justifiable to a certain extent only since he based his regions mainly upon the present distribution of the Passerine birds.
Unfortunately these six regions are not of equal value. The Indian countries and the Ethiopian region (Africa south of the Sahara) are obviously nothing but the tropical, southern continuations or appendages of one greater complex. Further, the great eastern mass of land is so intimately connected with North America that this continent has much more in common with Europe and Asia than with South America. Therefore, instead of dividing the world longitudinally as Sclater had done, Huxley, in 1868 ("On the classification and distribution of the Alectoromorphae and Heteromorphae", "Proc. Zool. Soc." 1868, page 294.), gave weighty reasons for dividing it transversely. Accordingly he established two primary divisions, Arctogaea or the North world in a wider sense, comprising Sclater's Indian, African, Palaearctic and Neartic regions; and Notogaea, the Southern world, which he divided into (1) Austro-Columbia (an unfortunate substitute for the neotropical region), (2) Australasia, and (3) New Zealand, the number of big regions thus being reduced to three but for the separation of New Zealand upon rather negative characters. Sclater was the first to accept these four great regions and showed, in 1874 ("The geographical distribution of Mammals", "Manchester Science Lectures", 1874.), that