Origin of Species Variorum

Comparison with 1866

Mr. B. D. Walsh, a distinguished entomologist of the United States, has lately called attention to some cases, analogous with those of local forms and geographical races, yet very different from them. These cases he has fully described under the terms of Phytophagic varieties and Phytophagic species. Most vegetable-feeding insects live on one kind of plant or on one group of plants; but some feed indiscriminately on many widely distinct kinds, yet this induces no change in them. Mr. Walsh, however, has observed other cases in which either the larva or mature insect, or both states, are thus affected by slight, though constant, differences in colour, or size, or nature of their secretions. In one case difference in food was accompanied by several slight but constant structural differences in the mature male alone. In other cases both males and females are thus slightly affected. Lastly, differences of food apparently cause more marked and constant differences in colour or structure, or in both combined, in the larva and in the mature insect. Forms modified to this degree are ranked by all entomologists as distinct, though allied, species of the same genus. The slighter differences, as in colour alone, and confined to the larva alone, to the mature insect alone, are almost invariably looked at as mere varieties. But no man can draw the line for others, even if he can do so for himself, and determine with certainly which of the several phytophagic forms to call varieties and which to call species. Mr. Walsh, who argues with much force that the different states have gradually passed into each other, is forced to assume that those forms, which it may be supposed would freely intercross, should be designated as varieties, whilst those which have probably lost this capacity for intercrossing should be called species. As the difference in all these cases clearly depends on the insects having long fed on perfectly distinct plants, intermediate links between the several forms thus produced cannot be expected to be found; though formerly such must have existed, connecting the present divergent forms with their common progenitor. The naturalist thus loses his best guide in determining whether to rank such doubtful forms as varieties or species. This likewise necessarily occurs with closely allied organisms, of doubtful value, which inhabit separate continents or distant islands. But when an animal or plant ranges over the same continent or inhabits many islands in the same archipelago, and presents different forms in the different areas, there is always a chance, which is not rarely successful, that intermediate forms may be discovered which will link together the extreme states; and these are then degraded to the rank of varieties.

Some few naturalists maintain that animals never present varieties; but then these same naturalists rank the slightest difference as of specific value; and when even the identically same form is met with in two distant countries, or in two distinct geological formations, they go so far as to believe that two separate species are hidden under the same dress. The term species thus comes to be a mere useless mental abstraction, implying and assuming a separate act of creation. It cannot, however, be disputed that many forms, considered by highly-competent judges as varieties, have so perfectly the character of species that they have been ranked by other highly-competent judges as good and true species. But to discuss whether such slightly different forms are rightly called species or varieties, before any definition of these terms has been generally accepted, is vainly to beat the air.

Text in this page (from paragraph 700, sentence 110 to paragraph 700, sentence 300, word 30) is not present in 1866

ornithologists consider our British red grouse as only a strongly-marked race of a Norwegian species, whereas the greater number rank it as an undoubted species peculiar to Great Britain. A wide distance between the homes of two doubtful forms leads many naturalists to rank both as distinct species; but what distance, it has been well asked, will suffice? if that between America and Europe is ample, will that between the Continent and the Azores, or Madeira, or the Canaries, or Ireland, be sufficient? Some few naturalists maintain that animals never present varieties; but then these same naturalists rank the slightest differences as of specific value; and when even the same identical form is met with in two distant countries, or in two quite distinct geological formations, they go so far as to believe that two separate species are hidden under the same dress. Finally, it cannot be disputed that many forms, considered by highly-competent judges as varieties, have so perfectly the character of species that they are ranked by other highly-competent judges as good and true species. But to discuss whether such slightly different forms are rightly called species or varieties, before any definition of these terms has been generally accepted, is vainly to beat the air. ↑

Many of the cases of strongly-marked varieties or doubtful species well deserve consideration; for several interesting lines of argument, from geographical distribution, analogical variation, hybridism, &c., have been brought to bear on the attempt to determine their rank. I will here give only a single instance,— the well-known one of the primrose and cowslip, or Primula vulgaris and veris. These plants differ considerably in appearance; they have a different flavour, and emit a different odour; they flower at slightly different periods; they grow in somewhat different stations; they ascend