E.B. Poulton (1890)

extracts from: The Colours of Animals. London: Kegan Paul, Trench, Trübner & Co Ltd

Poulton was the first to recognize the possibility of frequency-dependent selection, pp. 46-47, under the heading of "Dimorphism in Lepidopterous larvae":
If we breed from moths developed from the green larvae of, e.g., the Large Emerald, the larvae in the next generation are chiefly green, and after several generations there is little doubt that the brown form would become excessively rare; so also the green form would disappear if we bred from the brown varieties.  But in nature both forms are common, and therefore it is certain that both must be advantageous to the species, or one of them would quickly disappear.  I believe that it is a benefit to the species that some of its larvae should resemble brown and others green catkins, instead of all of them resembling either brown or green.  In the former case the foes have a wider range of objects for which they may mistake the larvae, and the search must occupy more time, for equivalent results, than in the case of other species which are not dimorphic.
... but no-one's perfect -- group selectionist thinking from pp. 160-161, under the heading of "The value of Warning Colours"
At first sight the existence of this group [of colours] seems to be a difficulty in the way of the general applicability of the theory of natural selection.  Warning Colours appear to benefit the would-be enemies rather than the conspicuous forms themselves, and the origin and growth of a character intended solely for the advantage of some other species cannot be explained by the theory of natural selection.  But the conspicuous animal is greatly benefited by its Warning Colours.  If it resembled its surroundings like the members of the other class, it would be liable to a great deal of accidental or experimental tasting, and there would be nothing about it to impress the memory of an enemy, and thus prevent the continuous destruction of individuals.  The object of Warning Colours is to assist the education of enemies, enabling them to easily learn and remember the animals which are to be avoided.  The great advantage conferred upon the conspicuous species is obvious when it is remembered that such an easy and successful education means an education involving only a small sacrifice of life.
Selection against rarity in warning colours, ... almost!  From pp. 186, under the heading "The causes which have determined the resemblance between between Warning Colours in different Insects"
Hence the causes which determine the frequent repetition of the same colours and markings in distasteful forms are as follows: (1) The fact that a limited number of colours and patterns are especially efficient in attracting the attention of enemies, and in thus facilitating their education; (2) the fact that the education of enemies is also rendered easy by requiring them to learn only a small number of patterns and colours; (3) the great additional advantage conferred by trading upon the reputation of a well-known and much-feared or much-disliked insect.
Poulton provided strong support for Darwin's sexual selection theory for male flamboyance against Wallace's natural selection alternative.  Evidence for females choosing aesthetically pleasing males (p. 297: "Sexual Selection tested by the courtship of Spiders") and against Wallace's alternatives (example headings: p. 316 "The necessity for Recognition can never explain the aesthetic value of the results produced", p. 322 "The hypothesis that sexual colouring is due to a surplus of vitality or is developed in relation to underlying structures").  There follows this summary: pp. 334-335, under the heading "The evidence for the gradual development of pattern suggests selective breeding"
The steps by which some of the most elaborate and wonderful appearances have arisen, are traced by Mr. Darwin in the most complete and convincing manner.  When we look at the marvellous eyes upon the train of a Peacock, or the more beautiful markings on the feathers of the male Argus Pheasant, it seems impossible that so wonderful and complete a result can have been produced by the aesthetic preferences of female birds.  And yet Mr. Darwin shows the relation between these characters and much simpler markings on other parts of the surface.  He proves that the one has been derived from the other by gradual modification, and he points to traces of the original marking which persist in the complex appearance to which it has given rise.  Such facts, while eminently suggestive of the progressive development of simple into complex markings by some selective agency, seem to be unexplained by any other theory. It is impossible to understand how any necessities for recognition, any changes in the internal organs, any increasing vitality, could cause the one form of marking to develop into the other, along lines which correspond with the attainment of a gradually increasing aesthetic effect.
Poulton was fond of coining new terms from Greek roots.  He coined the term "aposematism" for warning colours, along with many other terms some of which are still in use today such as "epigamic".  In a fold-out appendix table from the end of the book (after p. 340, entitled "The Colours of Animals Classified according to their Uses"):
Aposematic colours
= Warning Colours (, away;
, sign)
NOUN: Aposeme
DEFINITION: An appearance
which warns off enemies because
it denotes something unpleasant
or dangerous.

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