Darwin and Modern Science [196]
Darwin's original letter exists ("Life and Letters", III. pages 93, 94.), and in it we are told that he had taken the advice given by Bates: "You had better ask Wallace." After some consideration Wallace replied that he believed the colours of conspicuous caterpillars and perfect insects were a warning of distastefulness and that such forms would be refused by birds. Darwin's reply ("Life and Letters", III. pages 94, 95.) is extremely interesting both for its enthusiasm at the brilliancy of the hypothesis and its caution in acceptance without full confirmation:
"Bates was quite right; you are the man to apply to in a difficulty. I never heard anything more ingenious than your suggestion, and I hope you may be able to prove it true. That is a splendid fact about the white moths (A single white moth which was rejected by young turkeys, while other moths were greedily devoured: "Natural Selection", 1875, page 78.); it warms one's very blood to see a theory thus almost proved to be true."
Two years later the hypothesis was proved to hold for caterpillars of many kinds by J. Jenner Weir and A.G. Butler, whose observations have since been abundantly confirmed by many naturalists. Darwin wrote to Weir, May 13, 1869: "Your verification of Wallace's suggestion seems to me to amount to quite a discovery." ("More Letters", II. page 71 (footnote).)
RECOGNITION OR EPISEMATIC CHARACTERS.
This principle does not appear to have been in any way foreseen by Darwin, although he draws special attention to several elements of pattern which would now be interpreted by many naturalists as epismes. He believed that the markings in question interfered with the cryptic effect, and came to the conclusion that, even when common to both sexes, they "are the result of sexual selection primarily applied to the male." ("Descent of Man", page 544.) The most familiar of all recognition characters was carefully explained by him, although here too explained as an ornamental feature now equally transmitted to both sexes: "The hare on her form is a familiar instance of concealment through colour; yet this principle partly fails in a closely-allied species, the rabbit, for when running to its burrow, it is made conspicuous to the sportsman, and no doubt to all beasts of prey, by its upturned white tail." ("Descent of Man", page 542.)
The analogous episematic use of the bright colours of flowers to attract insects for effecting cross-fertilisation and of fruits to attract vertebrates for effecting dispersal is very clearly explained in the "Origin". (Edition 1872, page 161. For a good example of Darwin's caution in dealing with exceptions see the allusion to brightly coloured fruit in "More Letters", II. page 348.)
It is not, at this point, necessary to treat sematic characters at any greater length. They will form the subject of a large part of the following section, where the models of Batesian (Pseudaposematic) mimicry are considered as well as the Mullerian (Synaposematic) combinations of Warning Colours.
MIMICRY,--BATESIAN OR PSEUDAPOSEMATIC, MULLERIAN OR SYNAPOSEMATIC.
The existence of superficial resemblances between animals of various degrees of affinity must have been observed for hundreds of years. Among the early examples, the best known to me have been found in the manuscript note-books and collections of W.J. Burchell, the great traveller in Africa (1810-15) and Brazil (1825-30). The most interesting of his records on this subject are brought together in the following paragraphs.
Conspicuous among well-defended insects are the dark steely or iridescent greenish blue fossorial wasps or sand-wasps, Sphex and the allied genera. Many Longicorn beetles mimic these in colour, slender shape of body and limbs, rapid movements, and the readiness with which they take to flight. On Dec. 21, 1812, Burchell captured one such beetle (Promeces viridis) at Kosi Fountain on the journey from the source of the Kuruman River to Klaarwater. It is correctly placed among the Longicorns in his catalogue, but opposite to its
"Bates was quite right; you are the man to apply to in a difficulty. I never heard anything more ingenious than your suggestion, and I hope you may be able to prove it true. That is a splendid fact about the white moths (A single white moth which was rejected by young turkeys, while other moths were greedily devoured: "Natural Selection", 1875, page 78.); it warms one's very blood to see a theory thus almost proved to be true."
Two years later the hypothesis was proved to hold for caterpillars of many kinds by J. Jenner Weir and A.G. Butler, whose observations have since been abundantly confirmed by many naturalists. Darwin wrote to Weir, May 13, 1869: "Your verification of Wallace's suggestion seems to me to amount to quite a discovery." ("More Letters", II. page 71 (footnote).)
RECOGNITION OR EPISEMATIC CHARACTERS.
This principle does not appear to have been in any way foreseen by Darwin, although he draws special attention to several elements of pattern which would now be interpreted by many naturalists as epismes. He believed that the markings in question interfered with the cryptic effect, and came to the conclusion that, even when common to both sexes, they "are the result of sexual selection primarily applied to the male." ("Descent of Man", page 544.) The most familiar of all recognition characters was carefully explained by him, although here too explained as an ornamental feature now equally transmitted to both sexes: "The hare on her form is a familiar instance of concealment through colour; yet this principle partly fails in a closely-allied species, the rabbit, for when running to its burrow, it is made conspicuous to the sportsman, and no doubt to all beasts of prey, by its upturned white tail." ("Descent of Man", page 542.)
The analogous episematic use of the bright colours of flowers to attract insects for effecting cross-fertilisation and of fruits to attract vertebrates for effecting dispersal is very clearly explained in the "Origin". (Edition 1872, page 161. For a good example of Darwin's caution in dealing with exceptions see the allusion to brightly coloured fruit in "More Letters", II. page 348.)
It is not, at this point, necessary to treat sematic characters at any greater length. They will form the subject of a large part of the following section, where the models of Batesian (Pseudaposematic) mimicry are considered as well as the Mullerian (Synaposematic) combinations of Warning Colours.
MIMICRY,--BATESIAN OR PSEUDAPOSEMATIC, MULLERIAN OR SYNAPOSEMATIC.
The existence of superficial resemblances between animals of various degrees of affinity must have been observed for hundreds of years. Among the early examples, the best known to me have been found in the manuscript note-books and collections of W.J. Burchell, the great traveller in Africa (1810-15) and Brazil (1825-30). The most interesting of his records on this subject are brought together in the following paragraphs.
Conspicuous among well-defended insects are the dark steely or iridescent greenish blue fossorial wasps or sand-wasps, Sphex and the allied genera. Many Longicorn beetles mimic these in colour, slender shape of body and limbs, rapid movements, and the readiness with which they take to flight. On Dec. 21, 1812, Burchell captured one such beetle (Promeces viridis) at Kosi Fountain on the journey from the source of the Kuruman River to Klaarwater. It is correctly placed among the Longicorns in his catalogue, but opposite to its