UNIVERS, 



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THE PKINCIPLES OF HEEEDITY 



CHAPTER I 



THEORIES OF HEREDITY 



Definition of Heredity The multiplication of cells The Germ-plasm 

 The characters of living beings Inborn characters Acquired 

 characters Modifications Variations The Lamarckian doctrine of 

 Heredity. 



1. HEREDITY has been variously defined. Herbert Spencer 

 describes it as " the capacity of every plant and animal to 

 produce other individuals of a like kind." Weismann follows 

 Spencer very closely. According to him " the word heredity 

 in its common acceptance means that property of an organism 

 by which its peculiar nature is transmitted to its descendants." 

 The science of heredity may be defined as that science which 

 deals with the organic relationships of progenitors with 

 descendants. 



2. The systematic study of heredity is of very recent origin. 

 It dates, in effect, from the publication of Darwin's great 

 work The Origin of Species. No doubt many important facts 

 were known previously ; and Lamarck, Spencer, and others 

 had formulated theories of evolution which implied theories 

 of heredity. But so much of error was mingled with the 

 facts, and so much of ancient superstition incorporated with 

 the theories, that a great part of the value of both was lost. 

 The interest aroused by Darwin's speculations gave the 

 necessary stimulus. A body of earnest and in many cases 

 brilliant workers strove to increase the sum-total of our 

 accurate knowledge, to dig the truth out of the accretions of 

 fiction which had gathered round it during the process of 

 ages. To-day enough is known with certainty to justify the 

 erection of heredity into a study which is by no means the 

 least important of that group of studies which we gather 



