8i8 THE POPULAR SCIENCE MONTHLY. 



fication. It may be only one individual of many which, becomes 

 modified and transmits the modification to descendants ; it may be 

 but one species of a genus which, for similar reasons, supersedes 

 the rest which become extinct in time proportioned to pro- 

 lificacy. 



There is no reason to suppose that the history of organic life 

 has differed in this respect from that of inorganic. We need not 

 discuss here the question of catastrophism and uniformitarianism 

 in geology However much the latter prevails at the present time, 

 both have doubtless operated in the past. Catastrophism would 

 necessarily produce gaps, or saltations, in the palseontological 

 record, as only the more plastic species would adapt themselves 

 and survive under its influence. It is not gaps due to such causes 

 that are here to be considered, however, but those which occur in 

 uniform strata. Haldeman has most suggestively remarked that 

 the same mineral will crystallize with three, six, or twelve angles, 

 but not with five or seven, and he asks. Are the facts of organic 

 morphism subject to less definite laws ? Cope has drawn another 

 illustration from inorganic forces, in the three great changes in 

 water, from solid, liquid, and vapor, which take place suddenly 

 at what may be called two expression-points of the thermometer, 

 the many intervening degrees involving no change, Ehythm or 

 wave movement would seem to be a universal attribute of matter, 

 whether organic or inorganic. The forces of nature are constant, 

 but the phenomena induced are often paroxysmal. The progress- 

 ive forces accumulate, while the conservative forces resist, until at 

 last resistance gives way with comparative suddenness. There is 

 every reason to believe that the life-movement, in its ascending 

 complexity, has shared this common law. Accumulation is pro- 

 portioned to the change in environment, and resistance to the age 

 or rigidity of the organism. The latter may be strong enough to 

 end in death or extinction, or it may break down, and, with com- 

 paratively sudden yielding and conformity to necessity, burst the 

 confines and begin a new series of variations and adaptations. In 

 either case we have breaks, because the dying or dropping out of 

 one type makes room for another more accommodating. Rapid 

 evolution, from causes already discussed, implies gaps which must 

 be marked according as the strength of the conservative forces and 

 the violence of the final accommodation are great, and "because 

 certain breaks are more apt to occur after long periods of stability. 

 The break may be induced by changes in physical environment or 

 without such change ; if the latter, it will more likely occur in some 

 individual born with a marked departure from the type that gives 

 it some advantage, and whose issue will in time supplant all other 

 individuals. In either case we shall have, palseontologically, dis- 

 tinct species or genera, one superposed on the other, without links. 



