156 THE DOCTRINE OF DESCENT. 



various groups of living beings. The knowledge of 

 these pedigrees has now for the first time a truly sci- 

 entific purport, as compared with the old system of 

 types; for the genealogical trees cannot be constructed 

 without a knowledge of their growth, and of the causes 

 which produced their brariches, twigs, and shoots. 

 Each family thus includes all the forms derived from 

 one simple original form. The old systematic school 

 was obliged to content itself with working out the classi- 

 fication of the individual types, and defining their 

 limits, and then balancing the types against each other 

 on general morphological and physiological principles, 

 in order to estimate their relative value, all without any 

 consciousness of the natural causes of these actual 

 relations. The doctrine of Descent connects the 

 original forms of the types afresh from the point of 

 view of consanguinity, and descends deeper and deeper, 

 down to the simplest organisms, and the beginning of 

 life. 



But before we attempt to come to an understanding 

 as to the origin of life, one of the pillars of the doctrine 

 of Descent, it seems appropriate to allude to the question 

 whether natural selection, of which the means and effects 

 will be more minutely elucidated in the following chap- 

 ters, is capable of explaining all the modifications of or- 

 ganic beings, and whether selection must always be sum- 

 moned to aid in the explanation of these transformations? 

 In other words, whether the theory of selection answers 

 all the requirements of the doctrine of Descent, or 

 whether it is capable and in need of amendment? We 

 may do this with the more impartiality, as the acute 

 author of the book entitled " The Unconscious from the 



