PDF - Wallace Online

TROPICAL NATUEEincreasing complexity the outward mimicry which now soamazes us. During the long ages in which this process hasbeen going on, and the Danaidae have been acquiring thosespecialities of colour which aid in their preservation, many aLeptalis may have become extinct from not varying sufficientlyin the right direction and at the right time to keepup a protective resemblance to its neighbour and this well;accords with the comparatively small number of cases of truemimicry, as compared with the frequency of those protectiveresemblances to vegetableor inorganic objects whose formsare less definite and colours less changeable. About a dozenother genera of butterflies and moths mimic the Danaidse invarious parts of the world, and exactly the same explanationwill apply to all of them. They represent those species ofeach group which,at the time when the Danaidse firstacquired their protective secretions, happened outwardly toresemble some of them, and which have, by concurrent variationaided by a rigid selection, been able to keep up thatresemblance to the present day.lTheory of Sexual ColoursIn Mr. Darwin's celebrated work, The Descent of Man andSelection in Relation to Sex, he has treated of sexual colour incombination with other sexual characters, and has arrived atthe conclusion that all or almost all the colours of the higheranimals (including among these insects and all vertebrates)are due to voluntary or conscious sexual selection ;and thatdiversity of colour in the sexes is due, primarily, to the transmissionof colour-variations either to one sex only or to bothsexes, the difference depending on some unknown law, andnot being due to natural selection.I have long held this portion of Mr. Darwin's theory to beerroneous, and have argued that the primary cause of sexualdiversity of colour was the need of protection, repressing in1 For fuller information on this subject the reader should consult Mr.Bates' original paper, "Contributions to an Insect -fauna of the AmazonValley," in Transactions of the Linnean Society, vol. xxiii. p. 495 Mr.;Trimen's paper in vol. xxvi. p. 497 ;the author's essay on "Mimicry," etc.,already referred to ; and, in the absence of collections of butterflies, the platesof Heliconidae and Leptalidse, in Hewitson's Exotic Butterflies ;and Felder'sVoyage of the " Novara," may be examined.