EVOLUTION 1093 



not had time or opportunity to remedy we must reckon the fre- 

 quency with which animals can adjust their ways to novel conditions 

 of life. But if these habit-changes are studied it will be found, we 

 believe, that in the great majority of cases the changes affect not 

 instinctive promptings or racially enregistered routine, but ways 

 that have an intelligent or associative basis. Predominantly instinc- 

 tive animals tend to become stereotyped ; predominantly intelligent 

 animals remain educable. 



SUMMARY AS REGARDS VARIATION AND HEREDITY 



I. Organic Evolution is a natural process of racial change in a par- 

 ticular direction, in the course of which new forms emerge and are 

 estabUshed, alongside of or in place of the originative stock. 



2. The factors in organic evolution may be distinguished as 

 {a) originative or variational, {b) hereditary, (c) selective, and 

 (d) isolative. {a) The originative factors induce novelties or new 

 departures of some sort, which form the raw materials of possible 

 evolution, whether progressive or retrogressive, [b) The hereditary 

 relation determines whether new features are continued on, like 

 the old-established features; it determines the proportion of their 

 recurrence (if any) in the offspring. If a new variation is not 

 entailed on some of the progeny, it cannot be of direct value in 

 evolutionary change, though it may be of individual import during 

 the lifetime of its possessor. Thus heredity is a condition of evolu- 

 tion, and even if there were no progressive evolution there would 

 still be heredity, (c) In the course of the struggle for existence, 

 which includes all the reactions that living creatures make to 

 environing difficulties and limitations, there are many forms of 

 selection or sifting which secure some greater degree of survival or 

 success for those variants that are in some respect or respects fitter 

 than their fellows. The discriminate or differential siftmg or eUmina- 

 tion may lead to the immediate death of a novel variant, or it may 

 simply involve a shorter life or a smaller less successful family. But 

 the logic of the process is always the same — the relatively less fit 

 tend to survive, and thus a species slowly changes, {d) The process 

 of raising a new group of similar variants to the level of a true- 

 breeding stable variety or sub-species, and eventually to the level 

 of a discontinuous species, not readily fertile with its relatives, is 

 helped by numerous forms of isolation (geographical, seasonal, 

 habitudinal, etc.), which narrow the range of inter- crossing and 

 bring similar forms to breed together. Thus there are the four out- 

 standing factors — changing, entailing, sifting, and singling (varia- 

 tion, heredity, selection, and isolation). 



3. Variations are novelties distinguishing offspring from their 



