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 without 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 with 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 whether 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- 
