TEE COLOURATION OF BIRDS' EGGS. 453 



I do not think that because birds' eggs are in a state of panmixia, they 

 are more variable than they would be if subject to the action of natural 

 selection. 



I simply balieve that eggs show greater variation than the birds 

 themselves, because in the case of the former there is no force operating 

 to cut off considerable variations in all directions save one. If we take 

 any hundred adult animals and study the variations they exhibit, we are 

 dealing with, so to speak, a hundred picked animals, a hundred specially 

 sebcted creatures, a hundred organisms which have survived the weeding 

 process of natural selection. Since all animals are admirably adapted to 

 their environment, natural selection, so long as that environment remains 

 constant, merely acts as a restraining force by cutting off all abnormal 

 forms, — that is to say, all members of the species which vary greatly 

 from a given mean. It is only under a changing environment that 

 natural selection causes evolution or the origin of new species. Our 

 hundred animals, then, will be a hundred which have survived because 

 they exhibit only a i?rrall degree of variation. For this reason, 

 it is probable that naturalists are inclined to underestimate the amount 

 of variation of which organisms are capable. If this view be correct 

 and if eggs be, as I think, in a state of panmixia, then they should 

 exhibit greater degrees of variation than the birds themselves do. This 

 I beliwve is actually the case. I unfortunately know too little of birds ' 

 eggs to be able to speak with assurance, but I think that scientific egg- 

 collectors will bear me out that birds' eggs do exhibit very largo varia- 

 tions. It would also appear to be established that some eggs vary more 

 than others. This also applies to animals and plants. It would be 

 interesting to learn whether those species of birds which are most variable 

 lay the most variable eggs. I would therefore regard a collection of birds' 

 eggs as most valuable material for the study of variation and not as so 

 many examples of protective colouration. Of course this theory makes 

 no attempt to account for the origin of variations in birds' eggs ; 

 it does not explain why some should be uniformly coloured while 

 others should exhibit pencillings and markings. But the theory of sexual 

 selection fails to explain the beautiful markings on the feathers of a 

 peacock, and the theory of panmixia does not account for the origin of 

 the various colours which are exhibited by animals under domestication. 

 I do, however, think it possible that if birds' eggs be studied carefully, 

 they may throw some fresh light on the unknown causes of variation. 



