THE EVOLUTION OF BIRDS. 



15 



analogous to the various forces (or energy) which are characteristic of inorganic matter. 

 The one is as mysterious as the other. Both are equally inexplicable, equally unquestionable, 

 equally subject to inexorable law ; so much so indeed that a Wallace can predict the 

 discovery of a new species of moth in Madagascar as certainly as a Leverrier can foretell 

 the discovery of a new planet in the solar system. 



The difference between the two theories amounts to this. In the one case we have 

 accidental variation, in the other teleological variation ; but whereas the former is entirely 

 dependent upon the aid of protective selection, sexual selection, or some other kind of 

 selection, to advance a single step in the direction of evolution, the latter is self-sufficient, 

 and capable of producing unaided all the assumed results of evolution. 



But the advocates of accidental variation may reply that, in assuming the existence of 

 teleological variation, we are begging the question ; what we seek to explain is how variation 

 can be teleological ; we all know that it is teleological ; what the theory of Natural Selection 

 provides is a mechanical explanation of teleological variation. No doubt it attempts to do 

 so, but, so far as I am able to judge, an ever-increasing number of biologists are of the 

 opinion that it fails in the attempt. 



It may be objected that teleological variation is too mysterious to be accepted as a 

 scientific dogma ; but it nmst not be forgotten that many other accepted dogmas are equally 

 mysterious, such as chemical affinity or magnetic attraction. 



So many modifications are obviously caused by definite variation, as, for example, the 

 modifications of the wings of birds to suit their migratory habits — so many modifications 

 must have been caused by definite variation, as, for example, the deposit of colour upon 

 eggs in the oviduct to suit the habit of building in exposed situations — that it is very easy 

 to assume that all variation that survives, so as permanently to modify a species, is definite. 

 The laws which govern Energy (force or condition of inorganic matter) are so absolutely 

 mysterious that I am unable to see anything unscientific in the theory that organic matter 

 may also have its peculiar energy (forces or conditions), and that one of these produces the 

 effects which may be called beneficial or teleological variation. 



It is possible that the mystery of Evolution by descent with modification, caused by 

 teleological variation, may never be unravelled ; but the value of the theory of Evolution to 

 the biologist as a working hypothesis is not thereby lessened. It is impossible to be too 

 grateful to Darwin for having taught us the truth of Evolution. Many great men before 

 him said it was true, but it was reserved for Darwin to convince us of its truth. Darwin's 

 theory of Natural Selection may be modified, or even disproved and forgotten ; but the fact 

 will remain that no one man in the nineteenth century has exercised a tithe of the influence 

 on scientific thought that has been wielded by Darwin. As the Titan who destroyed the 

 fetish of Special Creation, Darwin stands as the most prominent object in the scientific 

 landscape of the present century. 



Difference 

 between the 

 two theories. 



Variation 

 that survives 

 generally 

 definite. 



Evolution 

 the result of 

 a force. 



The theory 

 of Evolution 

 as a working 

 hypothesis 

 unaffected. 



Obligation of 

 naturalists 

 to Darwin 

 immeasur- 

 able. 



