NATURAL SELECTION.

Hokitika Guardian, 3 November 1923, Page 4

NATURAL SELECTION.

ASPECTS OF THE PI! IXCIPLE. According to the theory of Charles Darwin, the principle of natural selection (manifested in this case through .sexual selection) is primarily responsible for the singing powers anil gaudy colours of the males of certain species of wild birds. The theory is that those colours and vocal powers have the special purpose of pleasing and attracting the female. Another famous authority in Professor Alfred Russel Wallace (the cu-discoverer with Darwin of the principle oi natural selection) adopted Darwin’s view in the first place, hut eventually either abandoned or modified i' If the question is examined in a detached and eritieal spirit, without any oi the prepossession of mind which allccts the vast majority of those who have coiue under the influence oi n

great original thinker and investigator. it will he found extremely dilliieult to get away from the readjusted view ol Wallace. Jl. iur instance, the theory is correct in the broad general sense, how comes it that there are so many exceptions to tile operation ol this principle ol sexual selection!' So tar as the majority of people are eanahle ol observing, there is no dilicroin c between the colouration, or tin- marking, of the male and female in such species as the while cockato > or the quail. Where there is any ddlVr. nee it i- admittedly, in the favour of the male, since the leinale has less conspicuous plumage. Why, it may he asked, should not the principle operate both ways!' If the male develops gaudy colours to attract the female, why should not the female have sii:ii' gay tints ill her plumage to attract the male.' ROTH SEXES AIM!. There is another disturbing factor here to. so far as the Darwinian theory is concerned. Among some species ol birds both sexes sing and both sexes have plumage which i- practically nt the same colour. Where such birds iiiv under consideration we scent oner that the theory loses its point. Take the collared luitcherhiids (('met inis destructor), for example. Excepting that the shading of the male is usually a little more sharply defined than that oj the female, their coloration is practically the same. Roth sexes sing. li'. then, the singing powers and the gorgeous colouring of some males are produced (under the ooeralion id this principle of sexual selection) iur the purpose oi attracting the female, why should there he such striking exceptions!' Clearly, the principle does not operate in either sense with butcherbirds. since belli sexes are songsters and the male has no vivid or predominant colouring in his plumage. Many other cases could be cited oi species of birds which show no marked difference in the colors of the two sexes.

In considering this question, of the sober and the. gaudy plumage of different sexes In certain numerous .species, there is one suggestive fact which cannot he ignored. Where the male is gaudy and the female of sober lint, the female usually dues the whole of the sitting in the nesting period. Where, on the other hand, the colours are practically the same, both rexes appear in take their turn on tic nest. This is notably tin- ease with birds which live on, or near to. the laifd • the quail fur instance. As a matter of fact the male ol some species ol quail seems to do more of the brooding and general “domestic" work than tic female, which anneals to lie lather a capricious and absent-minded mother in more ways than one. Ihe significance of the difference ol no.-ling habit as between those species in which the male is dist inct ly coloured, and tile species in which the (olouring is substantially uniform, seems io me to !»• unmistakable. What, it suggests is that the sober plumage of the female which does the brooding, is nature’s provision for rendering her more or less invisible to prowling enemies while she is on the nest. In short, it is hut another phase ol the protective colouration. or adaptinility to environment whieli is so common in w ild lit". In the preservation nt the species il is surely in I as iniportain that the lcma!e' should he protected (when brooding) bv her colouring as that the male should he gaudilv nrrnved 10 attract inn a lien) ion and satisfy her penchant for > ind tint- in the pro-matin;/; •

HHOTKITIVE ( DEOI'HINC. The male and the female crow are ol j.i'ael n ally the same colour. I n 'he brooding season protective colouring is not necessary where these birds are < (.uieeriied. Is'eause they tire quite, capnhie of guarding their eggs and their voiing without any such aid. Ij i any ease liroteitivo (olouriiig would he ot liltl" u-e. a- they have to build large ami conspicuous nests xvhi'Ti could not ho coii: oaled by mere harmony ol enxiroiilcnt. There are scores oi other species of birds among which the male has developed neither gaudy colours nor singing powers to tit tract, the female. It is at least suggestive that a very considerable percentage of these birds heleng to species in which the male and tin* female share the brooding and nest under conditions which render r imperative that they should have tveinir.se to all passible i onccalinent from the viexv of enemies. If xxe allow that there is substance in the Darwinian theory (that gaudily coloured males have been involved through the process ui’ sexual, or natural, selection operating over countless ages), then we must also allow that the evidence iu support of the commonly dull hues of Ihe fomnli' being due to flic need for her greater protection in ihe breeding season is al least equally weight v. For tin* most part, the eggs of birds which nest in dark places (hollows of trees lor example) are white. Eggs laid in open nests, on the other hand, are usually coloured to harmonise in some respects with the .surroundings. If

white eggs were laid In open nests they would, nl' course, bo vi.- illI;■ to on extent lbut would surely invito the attention 'il predatory creat.tires. It “coins to 1.0 much Ihf sumu with the brooding id the mule anil the female. Where both sexes brood there is no need for the one to he brightly coloured and the other of sober tint. Any such distinction would represent a constant danger in ihf breeding season. I>'cause the moment the bright bird took the nest the excess of colour would advertise its presence to enemies. Consequently where both sexes brood in turn il is essential that they should both possess inconspicuous colours—assuming that they had no other means of proteciion or defence.

Of course. Darwin was never dogmatic on this subject. 1.1 e was too great a man and too devoted a scientist for that. Ho frankly admitted that there were Haws in the chain of his reasoning and deductions—that some of the inconsistencies were unexplainable. If the great biologist had had opportunities to study the hird-lile of Australia he might have modified his views as Russel Wallace did. Wallace devoted eight or nine years to the observation of birds and insects in the .Malay Archipelago. hut, like Darwin, he had no first-hand knowledge of the wondcrtul avian world of Australia. Darwin, it may ho recalled, got as far inland as the Blue Mountains of Xew South Wales, but. lie does not appear to have been favourably impressed by what be saw of the country, and was glad to get out of it.