THE NATURE OF SPECIES
impassable. Such units were once supposed to exist, and they were called species, a word meaning a kind. The name species was given under the impression that, though each kind so designated might vary to some extent, the variations were restricted within limits that could not be transgressed. The differences between members of the same species were regarded as individual variations. Slight differences between plants and animals of the same species were recognized by careful observers, and the abrupt changes seen in sports and monstrosities attracted the attention of the curious. Many early authors placed no limit on the extent to which such variations might occur. Bacon observed a fern growing out of a willow and, instead of explaining it as a natural graft due to a windblown spore caught in a crack, regarded it as an offshoot due to some injury or some special influence. He also suggested that the stump of a felled beech might put forth birch, it being "a tree of a smaller kind which needeth less nourishment." Thus, according to Bacon, a beech might be developed into a birch by an unfavourable environment.
The belief in the fixity of species arose in the generation after Bacon. Herbert Spencer[1] attributed it to a literal acceptance of the Mosaic account of Creation, and it has often been credited to Milton, who relates, in Paradise Lost,[2] how, on the sixth day, in accordance with the Divine command,
Opening her fertile womb, teemed at a birth,
Innumerous living creatures, perfect forms,
Limbed and full grown.
But, as Professor Poulton has remarked, the belief in the sudden appearance of animals in their present forms was
- ↑ In 1852, reprinted in Essays, vol. Ⅰ, p. 583, 1868.
- ↑ Book Ⅶ, lines 387-500.
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