DISTRIBUTION. 411 



The general results, then, are these. Our knowledge of 

 distribution in Time, being derived wholly from the evidence 

 afforded by fossils, is limited to that geologic time of which 

 some records remain — cannot extend to those remoter times 

 the records of which have been obliterated. From these re- 

 maining records, which probably form but a small fraction 

 of the whole, the general facts deducible are these: — That 

 such organic types as have lived through successive epochs, 

 have almost universally undergone modifications of specific 

 and generic values — modifications which have commonly been 

 great in proportion as the period has been long. That besides 

 the types which have persisted from ancient eras down to our 

 own era, other types have from time to time made their ap- 

 pearance in -the ascending series of strata — types of which 

 some are lower and some higher than the types previously 

 recorded; but whence these new types came, and whether 

 any of them arose by divergence from the previously-recorded 

 types, the evidence does not yet enable us to say. That in 

 the course of long geologic epochs nearly all species, most 

 genera, and a few orders, have become extinct; and that a 

 species, genus, or order, which has once disappeared from the 

 Earth never reappears. And, lastly, that the Fauna now 

 occupying each separate area of the Earth's surface is very 

 nearly allied to the Fauna which existed on that area during 

 recent geologic times. 



§ 108. Omitting sundry minor generalizations, the exposi- 

 tion of which would involve too much detail, what is to be 

 said of these major generalizations ? 



The distribution in Space cannot be said to imply that or- 

 ganisms have been designed for their particular habitats and 

 placed in them ; since, besides the habitat in which each kind 

 of organism is found there are commonly other habitats, as 

 good or better for it, from which it is absent — habitats to 

 which it is so much better fitted than organisms now occupy- 

 ing them, that it extrudes these organisms when allowed the 



