PDF - Wallace Online
PDF - Wallace Online PDF - Wallace Online
366 TROPICAL NATUREmale to special developments of dermal appendages and colour,quite independently of sexual or any other form of selection."Thus the hump on the male zebu cattle of India, the tailof fat-tailed rams, the arched outline of the forehead in themales of several breeds of sheep, and the mane, the long hairson the hind legs, and the dewlap of the male of the Berbura"goatare all adduced by Mr. Darwin as instances of characterspeculiar to the male, yet not derived from any parentancestral form. Among domestic pigeons the character ofthe different breeds is often most strongly manifested in themale birds ;the wattles of the carriers and the eye- wattles ofthe barbs are largest in the males, and male pouters distendtheir crops to a much greater extent than do the females,while the cock fantails often have a greater number of tailfeathersthan the females. There are also some varieties ofpigeons of which the males are striped or spotted with black,while the females are never so spotted (Animals and Plantsunder Domestication,i.161) ; yet in the parent stock of thesepigeons there are no differences between the sexes either ofplumage or colour, and artificial selection has not been appliedto produce them.The greater intensity of coloration in the male, which maybe termed the normal sexual difference, would be furtherdeveloped by the combats of the males for the possession ofthe females. The most vigorous and energetic usually beingable to rear most offspring, intensity of colour, ifdependenton, or correlated with vigour, would tend to increase. Butas differences of colour depend upon minute chemical orstructural differences in the organism, increasing vigour actingunequally on different portions of the integument, and oftenproducing at the same time abnormal developments of hair,horns, scales, feathers, etc., would almost necessarily lead alsoto variable distribution of colour, and thus to the productionof new tints and markings. These acquired colours would,as Mr. Darwin has shown, be transmitted to both sexes orto one only, according as they first appeared at an early age,or in adults of one sex ;and thus we may account for someof the most marked differences in this respect. With theexception of butterflies, the sexes are almost alike in thegreat majority of insects. The same is the case in mammals
v COLOUKS OF ANIMALS 367and reptiles, while the chief departure from the rule occursin birds, though even here in very many cases the law ofsexual likeness prevails. But in all cases where the increasingdevelopment of colour became disadvantageous to thefemale, it would be checked by natural selection, and thusproduce those numerous instances of protective colouring inthe female only, which occur most frequently in these twogroups, birds and butterflies.Colour as a means of RecognitionThere is also, I believe, a very important purpose and useof the varied colours of the higher animals in the facility itaffords for recognition by the sexes or by the young of thesame species; and it is this use which probably fixes anddetermines the coloration in many cases. When differencesin the size and form of allied species are very slight, colouraffords the only means of recognition at a distance, or whilein motion ;and such a distinctive character must thereforebe of especial value to flying insects which are continually inmotion, and encounter each other, as it were, by accident.This view offers us an explanation of the curious fact thatamong butterflies the females of closely-allied species in thesame locality sometimes differ considerably, while the malesare much alike ; for, as the males are the swiftest and by farthe highest fliers, and seek out the females, it would evidentlybe advantageous for them to be able to recognise their truepartners at some distance off. This peculiarity occurs withmany species of Papilio, Diadema, Adolias, and Colias; andthese are all genera, the males of which are strong on thewing and mount high in the air. In birds such markeddifferences of colour are not required owing to their higherorganisation and more perfect senses, which render recognitioneasy by means of a combination of very slight differentialcharacters. 1This principle may perhaps, however, account for someanomalies of coloration among the higher animals. Thus,while admitting that the hare and the rabbit are colouredprotectively, Mr. Darwin remarks that the latter, while1 For numerous examples of recognition-colours in birds, see Darwinism,pp. 217-226.
- Page 332 and 333: 316 TROPICAL NATUREhumming-birds ma
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- Page 336 and 337: TROPICAL NATUREDisplay of Ornaments
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- Page 340 and 341: TROPICAL NATUREallied species on Ch
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- Page 356 and 357: 340 TROPICAL NATUREand emotions may
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- Page 360 and 361: 344 TROPICAL NATUREprotecting them
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- Page 368 and 369: 352 TROPICAL NATUREThe universal av
- Page 370 and 371: 354 TROPICAL NATUREMr. Darwin's Des
- Page 372 and 373: 356 TROPICAL NATUREexternal objects
- Page 374 and 375: 358 TROPICAL NATUREand Mr. Sorby ha
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- Page 380 and 381: TROPICAL NATUEEincreasing complexit
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- Page 392 and 393: 376 TROPICAL NATUREtion, and what m
- Page 394 and 395: 378 TROPICAL NATURENatural Selectio
- Page 396 and 397: TROPICAL NATUREaway with the rapidi
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- Page 406 and 407: 390 TROPICAL NATUREpum, while black
- Page 408 and 409: TROPICAL NATUREthe large brilliantl
- Page 410 and 411: 394 TROPICAL NATUREzones ;while, es
- Page 412 and 413: 396 TROPICAL NATUREthese differ gre
- Page 414 and 415: 398 TROPICAL NATUREvery minute and
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- Page 422 and 423: 406 TROPICAL NATUREThe seeds of a p
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v COLOUKS OF ANIMALS 367and reptiles, while the chief departure from the rule occursin birds, though even here in very many cases the law ofsexual likeness prevails. But in all cases where the increasingdevelopment of colour became disadvantageous to thefemale, it would be checked by natural selection, and thusproduce those numerous instances of protective colouring inthe female only, which occur most frequently in these twogroups, birds and butterflies.Colour as a means of RecognitionThere is also, I believe, a very important purpose and useof the varied colours of the higher animals in the facility itaffords for recognition by the sexes or by the young of thesame species; and it is this use which probably fixes anddetermines the coloration in many cases. When differencesin the size and form of allied species are very slight, colouraffords the only means of recognition at a distance, or whilein motion ;and such a distinctive character must thereforebe of especial value to flying insects which are continually inmotion, and encounter each other, as it were, by accident.This view offers us an explanation of the curious fact thatamong butterflies the females of closely-allied species in thesame locality sometimes differ considerably, while the malesare much alike ; for, as the males are the swiftest and by farthe highest fliers, and seek out the females, it would evidentlybe advantageous for them to be able to recognise their truepartners at some distance off. This peculiarity occurs withmany species of Papilio, Diadema, Adolias, and Colias; andthese are all genera, the males of which are strong on thewing and mount high in the air. In birds such markeddifferences of colour are not required owing to their higherorganisation and more perfect senses, which render recognitioneasy by means of a combination of very slight differentialcharacters. 1This principle may perhaps, however, account for someanomalies of coloration among the higher animals. Thus,while admitting that the hare and the rabbit are colouredprotectively, Mr. Darwin remarks that the latter, while1 For numerous examples of recognition-colours in birds, see Darwinism,pp. 217-226.
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