156 THE DOCTRINE OF DESCENT. 



pedigrees of the various groups of living beings. The 

 knowledge of these pedigrees has now for the first time 

 a truly scientific purport, as compared with the old 

 system of types; for the genealogical trees cannot be 

 constructed w^ithout a knowledge of their growth, and 

 of the causes which produced their branches, 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 w^th working out 

 the classification 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 bemore minutely elucidated in the following chapters, 

 is capable of explaining all the modifications of organic 

 beings, and w^hether selection must always be summoned 

 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 Stand- 



