Masterpieces of Science 



ordinary generation is once broken. The gradual 

 diffusion of dominant forms, with the slow modi- 

 fication of their descendants, causes the forms of 

 life, after long intervals of time, to appear as if 

 they had changed simultaneously throughout 

 the world. The fact of the fossil remains of each 

 formation being in some degree intermediate in 

 character between the fossils in the formations 

 above and below, is simply explained by their 

 intermediate position in the chain of descent. 

 The grand fact that all extinct beings can be 

 classed with all recent beings, naturally follows 

 from the living and the extinct being the off- 

 spring of common parents. As species have 

 generally diverged in character during their long 

 course of descent and modification, we can under- 

 stand why it is that the more ancient forms, or 

 early progenitors of each group, so often occupy 

 a position in some degree intermediate between 

 existing groups. Recent forms are generally 

 looked upon as being, on the whole, higher in the 

 scale of organization than ancient forms; and 

 they must be higher, in so far as the later and 

 more improved forms have conquered the older 

 and less improved forms in the struggle for life; 

 they have also generally had their organs more 

 specialized for different functions. This fact is 

 perfectly compatible with numerous beings still 

 retaining simple but little improved structures, 

 fitted for simple conditions of life; it is likewise 

 compatible with some forms having retrograded 

 in organization, by having become at each stage 

 12 



