CiiAi'. XIV. •recapitulation. 425 



same coinph^x laws in tlieir deforces and kinds of resemblance 

 to their parents — in Ix'in;];' al)sorbcd into each other by suc- 

 cessive crosses, and in other such points — as do the crossed 

 oll'spring^ of aeknowledij^ed varieties. Tiiis sinuhiritj would be 

 a strange fact, if species liave been independently created and 

 varieties have been produced thronj^h secondary' laws. 



If we admit that the geolog-ical record is imperfect ia an 

 extreme degree, then the facts, which the record does give, 

 strongly support the theory of descent with modification. 

 New species have come on the stage slowly and at successive 

 intervals ; and the amount of change, after equal intervals of 

 time, is widely different in different groups. The extinction 

 of species and of whole groups of species, which has played so 

 conspicuous a part in the history of the organic world, almost 

 inevitably follows from the princii)le of natural selection ; for 

 old forms are supplanted by new and improved forms. Neither 

 single species nor groups of species reappear when the chain 

 of ordinary generation is once broken. Tlie gradual diffusion 

 of dominant forms, with the slow modification of their descend- 

 ants, 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 simpl}' ex])lained 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 liWng and the extinct being 

 the ofispring of common parents. As species have generally 

 diverged in character during their long course of descent and 

 modiiication, we can understand why it is that the more an- 

 cient forms of early progenitors of each group so often occu- 

 py a position in some degree intermediate between existing 

 groups. Recent forms are generally looked at as being, on 

 the whole, higher in the scale of organization than ancient 

 forms ; and they must bo higher, in so far as the later and 

 more improved forms have conqu(>red the older and less im- 

 proved forms in the struggle of life; they have also generally 

 had their organs more spccializtnl for different functions. This 

 fact is ])('rfectly cfjmpatible with numerous beings still retain- 

 ing simpl(! and but little improved structures, iitled for simple 

 condilicjns of life ; it is likewise compatible with some forms 

 haWng retrograded in organization, by having become at each 

 stage of descent better fitted for changed and degraded habits 



