June 8, 1900 ] 



SCIENCE 



889 



frequently disappear when the old condi- 

 tions are reverted to. 



With regard to these variations, we want 

 to ask the following question : Do they ever 

 last after the producing cause of them is 

 removed, and are they transmitted in re- 

 production ? In a great number of cases 

 thej' either cease when the cause which has 

 produced them is removed, or if they last 

 the life of the individual they are not trans- 

 mitted in reproduction. But is this always 

 the case ? That is the important question 

 we now have to consider. 



But before doing so let us inquire what 

 acquired characters really are. The so- 

 called adults of all animals have, as part of 

 their birthright, a certain plasticity in their 

 capacity of reacting to external influences ; 

 they all have a certain power of acquiring 

 bodily and mental characters under the in- 

 fluence of appropriate stimuli. This power 

 varies in degree and in quality in different 

 species. In plants, for instance, it is mainly 

 displayed in habit of growth, form of foli- 

 age, etc.; in man in mental acquirements, 

 and so on. But however it is displayed, it 

 is this property of organisms which permits 

 of the acquisition of those modifications of 

 structure which have been so widely dis- 

 cussed as acquired characters. Now this 

 power, when closely considered, is in reality 

 only a portion of that capacity for develop- 

 ment which all organisms possess, and with 

 which they become endowed at the act of 

 conjugation. A newly formed zygote pos- 

 sesses a certain number of hidden proper- 

 ties which are not able to manifest them- 

 selves unless it is submitted to certain ex- 

 ternal stimuli. It is these stimuli which 

 constitute the external conditions of exis- 

 tence, and the properties of the organism 

 which are only displayed under their influ- 

 ence are what we call acquired characters. 

 They are acquired in response to the exter- 

 nal stimuli. 



It would appear, then, that every feature 



which successively appears in an organism 

 in the march from the uninucleated zygote 

 to death is an acquired character. At first 

 the stimuli which are necessary are quite 

 simple, being little more than appropriate 

 heat and moisture; later on they become 

 more complicated, until finally, when the 

 developmental period is over and the ma- 

 ture life begins, the necessary conditions 

 attain their greatest complexity, and their 

 fulfilment constitutes what we call in the 

 higher animals education. Education is 

 nothing more than the response of the nearly 

 mature organism to external stimuli, the 

 penultimate response of the zygote to ex- 

 ternal stimuli, the ultimate being those of 

 senile decay, which end in natural death. 

 Acquired properties, it will be seen, are 

 really stages in the developmental history. 

 They differ in the complexity of the stim- 

 ulus required to bring them out. For in- 

 stance, the segmentation of the egg requires 

 little more than heat and moisture, the 

 walking of the chick the stimulus of light 

 and sound and gravity, the evolutions of an 

 acrobat the same in greater complexity, and 

 lastly the action of a statesman requires 

 the stimulation of almost every sense in the 

 greatest complexity. Moreover, not only 

 are there differences in the complexity of 

 the stimulus required, but also in the ra- 

 pidity with which the organism reacts to it. 

 The chick undergoes its whole embryonic 

 development in three weeks, a man in nine 

 months ; the chick develops its walking 

 mechanism in a few minutes, while a man 

 requires twelve months or more to effect 

 the same end. Chickens are much cleverer 

 than human beings in this respect. There 

 is the same kind of difference between them 

 that there is between the power of learning 

 displayed by a Macaulay and that displayed 

 by a stupid child. 



An instinct is nothing more than an in- 

 ternal mechanism which is developed with 

 great rapidity in response to an appropriate 



