H2 THE GENESIS OF SPECIES. JChap. 



CHAPTER VI. 



SPECIES AND TIME. 

 \ 



Two IJelations of Species to Time. — No Kvidence of Tast Existence of Minutely- 

 iiiteniieiliatu Forms when such might bo expoctcd a priori. — Hats, I'toioduc- 

 tyis, DiiiosaurLi, and IJirds. — Ichthyosauria, Ciiolouia, and Anoura. — llwse An- 

 cestry. — Ijibyrinthodonts and Tiiiohitcs. — Twy Subdivisions of the Second lida- 

 tion of Species to 'lime. — Sir William Tiiomson's Views. — rrobable Period re- 

 qiiin;d fur Ultimate Sitecillo JCvolnlion from Primitive Ancestral Forms. — (Jeo- 

 nu'trical Ijicrease of 'I'lme re<iuircd for Itupldly-mulliplyliij,' Increase of Stnicliiral 

 Dillireucofl. — I'roboHcis Monkey. — 'I'imc reiiulred fur Dcpo.iitlon of Btratii iieces- 

 6ury for Darwinian Evolution. — High Organiziitlon of Silurian Forms of Life. — 

 Absence of FossILj in Oldest Kocks. — Summary and O-onehision. 



Two considerations present themselves with reg-anl to 

 the necessary rehition of species to time if tlie theory of 

 "Natural Selection" is valid and sufficient. 



The first is with regard to the evidences of tlie past ex- 

 istence of intermediate forms, their duration and succession. 



The second is with rciTJU'd to the total amount of time 

 required for the evolution of all organic forms from a few 

 original ones, and the bearing of other sciences on tliis 

 question of time. 



As to the first consideration, evidence is as yet against 

 the modification of species by " Natural Selection " alone, 

 because not only are minutely transitional forms generally 

 absent, but they are absent in cases where we might cer- 

 tainly a priori have expected them to be present. 



Now it has been said:* "If Mr. Darwin's theory l)e 

 true, the number of varieties diifering one from another a 



* North British Review^ New Series, vol. vii., March, 1867, p. 31 7. 



