IN BORNEAN FORESTS [chap. 



notwithstanding this, no new estuarine plant has been formed in 

 our times ; thus fully proving the reluctance in existing organisms 

 to abandon the prerogatives with which the past with cumulative 

 effect has endowed them. 



Not admitting that at the present day species can vary, or that 

 organisms are capable of an appreciable degree of adaptability to 

 surrounding conditions, and at the same time holding natural and 

 sexual selection as insufficient to explain all the phenomena of 

 evolution, the question arises in what way has evolution taken 

 place ? 



The answer appears to me easy and obvious. What does not 

 happen now can nevertheless have happened in the past. 1 



I take it to be a great philosophical error to persist in considering 

 past biological and telluric phenomena as having been produced by 

 forces identical in nature and intensity with those in action at the 

 present day, j ust as I believe it a mistake to draw too close a parallel 

 between what happened in earlier geological periods with what 

 daily takes place under our own eyes. It would be almost tanta- 

 mount to arguing that a baby is in every way identical with an 

 old man ! 



As far as life is concerned, one of the chief differences between 

 the present and the past in my opinion exists in the intensity with 

 which the force known as " conservative heredity " manifests itself, 

 obliging modern organisms to transmit unaltered to their descend- 

 ants the shape, colours, peculiarities, in short, the entire characters 

 which were transmitted to them by their ancestors. This is the 

 reason why now living beings are, so to speak, fixed and immutable, 

 and cannot assume absolutely new forms. For the very same 

 reason external agents with their stimuli cannot succeed in producing 

 important modifications in the stimulated organs during the lifetime 

 of individuals, and much less can modifications casually obtained 

 in the organism during life be transmitted to its progeny. If, as 

 an instance, we take a monkey which has been trained to stand 

 erect on its legs, and which has also acquired the requisite muscular 

 development for such a gait, it can never transmit to its offspring 

 either the acquired faculty of standing erect, or the muscular 

 development thus obtained. Thus heredity is the obstacle which 

 prevents variation in species now living, or permits it in so small 

 a degree, that even the accumulation of small variations during 

 myriads of years could never have rendered possible the evolution 

 of the organic world, if it has to be thus accounted for. 



If, however, one considers that the action of conservative here- 

 dity cannot have been always the same, that, necessarily feeble in 



1 The first mention of this hypothesis of mine was briefly made in a paper 

 I published in the Bullettino delta R. Societa Toscana dOrticultura, Anno 

 xiv. (1889), bearing the title " Fioritura dell' 'Amorpho 'phallus titanum." 



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