THE ARGUMENTS FROM DISTRIBUTION. 399 



have been thus developed, though we are without evidence that 

 they have been so ; yet that " any admissible hypothesis of 

 progressive modification must be compatible with persistence 

 without progression through indefinite periods." JSTow these 

 results are quite congruous with the hypothesis of evolution. 

 As rationally interpreted, evolution must in all cases be 

 understood to result, directly or indirectly, from the incidence 

 of forces. If there are no changes of conditions, entailing 

 organic changes, organic changes are not to be expected. 

 Only in organisms which fall under conditions, in conformity 

 to which there arise additional modifications answering to 

 additional needs, will there be that increased heterogeneity 

 which characterizes higher forms. Hence, though the facts 

 of palaeontology cannot be held to prove evolution, yet they 

 are in harmony with it ; and some few of them yield it 

 support. 



§ 141. One general truth respecting distribution in Time, 

 is, however, profoundly significant. If, instead of contem- 

 plating the relations among past forms of life taken by them- 

 selves, we contemplate the relations between them and the 

 forms now existing ; we find a connexion which is in perfect 

 harmony with the belief in evolution, but quite irreconcil- 

 able with any other belief. 



Note, first, how full of meaning is the close kinship that 

 exists between the aggregate of organisms now living, 

 and the aggregate of organisms which lived in the most 

 recent geologic times. In the last-formed strata, nearly all 

 the imbedded remains are those of species which still flourish. 

 Strata a little older, contain a few fossils of species now ex- 

 tinct ; though, usually, species greatly resembling extant ones- 

 Of the remains found in strata of still earlier date, the ex- 

 tinct species form a larger per centage ; and the differences be- 

 tween them and the allied species now living, are more marked. 

 That is to say, the gradual change of organic types in Time, 

 which we before saw is indicated by the geological record, is 



