No. 579] PROGRESSIVE EVOLUTION 



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eration a start in life. There is every reason to believe 

 that this has been a progressive process throughout the 

 whole course of evolution, for the higher the degree or 

 organization the more perfect do we find the arrange- 

 ments for securing the welfare of the offspring. 



We cannot, of course, trace this process back to its 

 commencement, because we know nothing of the nature 

 of the earliest living things, but we may pause for a 

 moment to inquire whether any phenomena occur 

 amongst simple unicellular organisms that throw any 

 light upon the subject. What we want to know is — How 

 did the habit of accumulating surplus energy and hand- 

 ing it on to the next generation first arise? 



Students of Professor H. S. Jennings's admirable 

 work on the " Behavior of the Lower Organisms" will 

 remember that his experiments have led him to the con- 

 clusion that certain Protozoa, such as Stentor, are able 

 to learn by experience how to make prompt and effective 

 responses to certain stimuli; that after they have been 

 stimulated in the same way a number of times they make 

 the appropriate response at once without having to go 

 through the whole process of trial and error by which it 

 was first attained. In other words, they are able by 

 practise to perform a given action with less expenditure 

 of energy. Some modification of the protoplasm must 

 take place which renders the performance of an act the 

 easier the oftener it has been repeated. The same is, 

 of course, true in the case of the higher animals, and we 

 express the fact most simply by saying that the animal 

 establishes habits. From the mechanistic point of view 

 we might say that the use of the machine renders it more 

 perfect and better adapted for its purpose. In the 

 present state of our knowledge I think we cannot go be- 

 yond this, but must content ourselves with recognizing 

 the power of profiting by experience as a fundamental 

 property of living protoplasm. 



It appears to me that this power of profiting by ex- 

 perience lies at the root of our problem, and that in it 



