C— 6E0L0GS-. 69 



Here, then, is a difficulty. It can be overcome in two ways. A 

 view held by many is that there are two kinds of characters : first, those 

 {hat arise from changes in the germ, and appear as sudden or discon- 

 tinuous variations; second, those that are due to external (i.e., non- 

 germinal) factors. It seems a corollary of this view that the external 

 characters should so affect the germ-plasm as ultimately to produce in 

 it the appropriate factors. This is inheritance of acquired characters. 

 The other way out of the difliculty is to suppose that all characters 

 o^er than fluctuations or temporary modifications are germinal ; that 

 changes are due solely to changes in the constitution of the germ; and 

 that, although a hew character may not manifest itself till the creature 

 has reached old age, nevertheless it was inherent in the germ and latent 

 through the earlier growth-stages. This second hypothesis involves 

 two further difficulties. It is not easy to formulate a mechanism by 

 which a change in the constitution of the germ shall produce a character 

 of which no trace can be detected until old age sets in ; such a character, 

 for instance, as the tuberculation of the last-formed portion of an 

 ammonite shell. Again, it is generally maintained that characters due 

 to this change of germinal factors, however minute they may be, make 

 a sudden appearance. They are said to be discontinuous. They act 

 as integral units. Now the characters we are trying to explain seem 

 to us palaeontologists to appear very gradually, both in the individual 

 and in the race. Their beginnings are small, scarcely perceptible; they 

 increase gradually in size or strength; and gradually they appear at 

 earlier and earlier stages in the life-cycle. It appears least difficult to 

 suppose that characters of this kind are not initiated in the germ, and 

 that they, if no others, may be subject to recapitulation. It may not 

 yet be possible to visualise the whole process by which such characters 

 are gradually established, or to refer the phenomena of recapitulation 

 back to more fundamental principles. But the phenomena are there, 

 and if any hypothesis is opposed to them so much the worse for the 

 hypothesis. However they be explained, the instances of recapitula- 

 tion afford convincing proof of descent, and so of genetic evolution. 



The ' Line upon Line ' Method of Palaeontology. 



You will have observed that the precise methods of the modern 

 palaeontologist, on which tliis proof is based, are very different from the 

 slap-dash conclusions of forty years ago. The discovery of Archae- 

 opteryx, for instance, was thought to prove the evolution of Birds from 

 Reptiles. No doubt it rendered that conclusion extremely probable, 

 especially if the major premiss — that evolution was the method of 

 nature — were assumed. But the fact of evolution is precisely what 

 men were then trying to prove. These jumpings from Class to Class 

 or from Era to Era, by aid of a few isolated stepping-stones, were whst 

 Bacon calls Anticipations, ' hasty and premature ' but * very effective, 

 because as they are collected from a few instances, and mostly from 

 those which are of familiar occurrence, they immediately dazzle the 

 intellect and fill the imagination ' (Nov. Org. I. 28). No secure step 

 was taken until the modern palaeontologist began to affiliate mutation 

 with mutation and species \vith species, working his way back, literally 



