THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 291 



would bring about an increase of size in the muscles and bones of the nock and 

 shoulders entirely analogous to that observed in Megaceros. This may be an 

 ontogenetic adaptation. 



3. Heredity, including Variation. 1 



By heredity we mean the forces or conditions embodied in the "stirp" of 

 Galton, in the "germ plasm" of Weismann, in the "genes" of Johannsen, in the 

 "determiners" or "factors" of other authors. We use heredity in this sense 

 as one of the four factors rather than coin a new name. That is, heredity is 

 conceived as the continuity of forces resident in the blastos rather than in its 

 outward or visible expression in the soma as what are known as hereditary char- 

 acters. Thus heredity includes the germinal, blastogenic, congenital or native 

 conditions of "nature" as distinguished from the "nurture" conditions. It is 

 the seat of the behavior of all the characters which are transmissible or heritable. 



I leredity, as is clearly understood by some authors and not by others, includes 

 both hereditary repetition and hereditary variation, as distinguished from 

 ontogenic variation. Thus variation is an included principle within heredity 

 and not an opposed principle. There is no reason in the often repeated phrase 

 that "evolution is through heredity, variation, and other factors." 



While heredity is chiefly remarkable as the conservative force, palaeontology 

 proves that there is a strong progressive element in it; that is, in some unexplained 

 manner new properties and potentialities are constantly being added to the 

 blastos, or material basis of heredity. 



Some of the ontogenic or phenotypic "characters" which are the outward 

 expression of the predispositions and potentialities of heredity are the following: 



1. Repetitions of parental and ancestral type = the heredity of some writers, including "char- 



acters" occurring late in life which are apparently somatogenic but in reality blastogenic. 



2. Predispositions, structural and functional. 



3. Recapitulations of ancestral history, 



(a) regressions, 



(6) reversions. 



4. Abbreviations of ancestral history, intercalations. 



5. Fluctuations in plasticity, modifiability, adaptability. 



6. Fluctuations in susceptibility of immunity to certain diseases. 



7. Correlations of (a) functionally related characters, (6) functionally unrelated characters. 



8. Variations of Darwin in part = Mutations.* 

 Also variations of Darwin in part = Fluctuations. 



Heredity, fluctuations in Quetelet's 

 Recessives (Mendel), also latent chs 

 Dominants (Mendel), also patent cl 

 Contemporaneous and sudden varia" 

 variations," "saltations," "sports, 



» << 



owing the Quetelet law, includ 

 is " of De Vries (not of Waage 



1 Osborn, H. F. : Evolution and Heredity. Biological Lectures, Marine Biological Laboratory 

 Woods Hole, 1890. Ginn & Company, Boston. Are A 

 discussion UDon th« T.ftmnrnkion PrinpiJfl ;« TCirsii„+; n « 



Inherited? Opening 



lution. American Society of Naturalists, Boston, 



Dec. 31, 1890. Amer. Naturalist, vol. XXV. No. 291. Mar. 1891. dp. 191-216. The Present Problem 



Atlantic Monthly. Mar 



Heredity in the Ovum and Spermatozoon 



Wood's Reference Handbook of the Medical Sciences, pp. 396-408. W. Wood 



2 Osborn, H. F., Darwin's Theory of Evolution by the Selection of Minor Saltations, Amer 

 alist, vol. XLVI, Feb., 1912. pp. 76-82. 



