GEOLOGICAL SUCCESSION OF ORGANIC BEINGS i2\ 



We can understand how it is that dominant forms which spread 

 widely and yield the greatest number of varieties tend to people 

 the world with aUied, but modified, descendants; and these wil 

 generally succeed in displacing the groups which are their in- 

 feriors in the struggle for existence. Hence, after long intervals 

 of time, the productions of the world appear to have changed 

 simultaneously. 



We can understand how it is that all the forms of life, ancient 

 and recent, make together a few grand classes. We can under- 

 stand, from the continued tendency to divergence of character, 

 why, the more ancient a form is, the more it generally differs from 

 those now living; why ancient and extinct forms often tend to 

 fill up gaps between existing forms, sometimes blending two 

 groups, previously classed as distinct, into one; but more com- 

 monly bringing them only a little closer together. The more 

 ancient a form is, the more often it stands in some degree inter- 

 mediate between groups now distinct; for the more ancient a 

 form is, the more nearly it will be related to, and consequently 

 resemble, the common progenitor of groups, since become widely 

 divergent. Extinct forms are seldom directly intermediate be- 

 tween existing forms; but are intermediate only by a long and 

 circuitous course through other extinct and different forms. We 

 can clearly see why the organic remains of closely consecutive 

 formations are closely allied; for they are closely linked together 

 by generation. We can clearly see why the remains of an inter- 

 mediate formation are intermediate in character. 



The inhabitants of the world at each successive period in its 

 history have beaten their predecessors in the race for life, and 

 are, in so far, higher in the scale, and their structure has generally 

 become more speciaHzed; and this may account for the common 

 belief held by so many palaeontologists, that organization on the 

 whole has progressed. Extinct and ancient animals resemble to 

 a certain extent the embryos of the more recent animals belonging 

 to the same classes, and this wonderful fact receives a simple 

 explanation according to our views. The succession of the same 

 types of structures within the same areas during the later geo- 

 logical periods ceases to be mysterious, and is intelligible on the 

 principle of inheritance. 



If, then, the geological record be as imperfect as many believe, 

 and it may at least be asserted that the record cannot be proved 

 to be much more perfect, the main objections to the theory of 

 natural selection are greatly diminished or disappear. On the 

 other hand, all the chief laws of palaeontology plainly proclaim, 



