PDF - Wallace Online
PDF - Wallace Online PDF - Wallace Online
TROPICAL NATURErunning to its burrow, is made conspicuous to the sportsman,and no doubt to all beasts of prey, by its upturned white tail.But this very conspicuousness while running away, may beuseful as a signal and guide to the young, who are thusenabled to escape danger by following the older rabbits,directly and without hesitation, to the safety of the burrow ;and this may be the more important from the semi-nocturnalhabits of the animal. If this explanation is correct, and itcertainly seems probable, it may serve as a warning of howimpossible it without exact is, knowledge of the habits of ananimal and a full consideration of all the circumstances, todecide that any particularcoloration cannot be protective orin any way useful. Mr. Darwin himself is not free from suchassumptions. Thus, he " says: The zebra is conspicuouslystriped, and stripes cannot afford any protection on the openplains of South Africa." But the zebra is a very swiftanimal, and, when in herds, by no means void of means ofdefence. The stripes therefore may be of use by enablingstragglers to distinguish their fellows at a distance, and theymay be even protective when the animal is at rest amongherbage the only time when it would need protective colouring.Until the habits of the zebra have been observed withspecial reference to these points, it is surely somewhat hastyto declare that the stripes "cannot afford any protection." 1Colowr proportionate to Integumentary DevelopmentThe wonderful display and endless variety of colour inwhich butterflies and birds so far exceed all other animals,seems primarily due to the excessive development and endlessvariations of the integumentary structures of these twogroups. No insects have such widely expanded wings in proportionto their bodies as butterflies and moths in none do;the wings vary so much in size and form, and in none are theyclothed with such a beautiful and highly-organised coating ofscales. According to the general principles of the productionof colour already explained, these long continued expansions ofmembranes and developments of surface-structures must haveled to numerous colour-changes, which have been sometimeschecked, sometimes fixed and utilised, sometimes intensified,1For further information on this point, see Darwinism, p. 220,
v COLOURS OF ANIMALS 369by natural selection, according to the needs of the animal.In birds, too, we have the wonderful clothing of plumagethe most highly organised, the most varied, and the mostexpanded of all dermal appendages. The endless processes ofgrowth and change during the development of feathers, andthe enormous extent of this delicately-organised surface, musthave been highly favourable to the production of variedcolour-effects, which, when not injurious, have been merelyfixed for purposes of specific identification, but have oftenbeen modified or suppressed whenever different tints wereneeded for purposes of protection.Selection by Females not a cause of ColourTo conscious sexual selection that is, the actual choice bythe females of the more brilliantly -coloured males or therejection of those less gaily coloured I believe very little ifany effect is directly due. It is undoubtedly proved that inbirds the females do sometimes exert a choice; but theevidence of this fact, collected by Mr. Darwin (Descent of Man,chap, xiv.), does not prove that colour determines that choice,while much of the strongest evidence is directly opposed tothis view. All the facts appear to be consistent with thechoice depending on a variety of male characteristics, withsome of which colour is often correlated. Thus it is theopinion of some of the best observers that vigour and livelinessare most attractive, and these are no doubt usuallyassociated with intensity of colour. Again, the display of thevarious ornamental appendages of the male during courtshipmay be attractive ;but these appendages, with their brightcolours or shaded patterns, are due probably to general lawsof growth, and to that superabundant vitality which we haveseen to be a cause of colour. But there are many considerationswhich seem to show that the possession of these ornamentalappendages and bright colours in the male is not animportant character functionally, and that it has not beenproduced by the action of conscious sexual selection. Amidthe copious mass of facts and opinions collected by Mr.Darwin as to the display of colour and ornaments by the malebirds, there is a total absence of any evidence that the females,as a rule, admire or even notice this display. The hen, the2B
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TROPICAL NATURErunning to its burrow, is made conspicuous to the sportsman,and no doubt to all beasts of prey, by its upturned white tail.But this very conspicuousness while running away, may beuseful as a signal and guide to the young, who are thusenabled to escape danger by following the older rabbits,directly and without hesitation, to the safety of the burrow ;and this may be the more important from the semi-nocturnalhabits of the animal. If this explanation is correct, and itcertainly seems probable, it may serve as a warning of howimpossible it without exact is, knowledge of the habits of ananimal and a full consideration of all the circumstances, todecide that any particularcoloration cannot be protective orin any way useful. Mr. Darwin himself is not free from suchassumptions. Thus, he " says: The zebra is conspicuouslystriped, and stripes cannot afford any protection on the openplains of South Africa." But the zebra is a very swiftanimal, and, when in herds, by no means void of means ofdefence. The stripes therefore may be of use by enablingstragglers to distinguish their fellows at a distance, and theymay be even protective when the animal is at rest amongherbage the only time when it would need protective colouring.Until the habits of the zebra have been observed withspecial reference to these points, it is surely somewhat hastyto declare that the stripes "cannot afford any protection." 1Colowr proportionate to Integumentary DevelopmentThe wonderful display and endless variety of colour inwhich butterflies and birds so far exceed all other animals,seems primarily due to the excessive development and endlessvariations of the integumentary structures of these twogroups. No insects have such widely expanded wings in proportionto their bodies as butterflies and moths in none do;the wings vary so much in size and form, and in none are theyclothed with such a beautiful and highly-organised coating ofscales. According to the general principles of the productionof colour already explained, these long continued expansions ofmembranes and developments of surface-structures must haveled to numerous colour-changes, which have been sometimeschecked, sometimes fixed and utilised, sometimes intensified,1For further information on this point, see Darwinism, p. 220,
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