CAUSES OF THE EVOLUTION AND EXTINCTION OF THE TITANOTHERES 



849 



also act upon the physico-chemical messengers to the 

 germ cells, the activities of which correspond poten- 

 tially with certain activities of the body cells (Osborn, 

 1917.462, pp. 77-78). 



GEEMINAI it) ALIOMETEONS INFIDENCED BY 0E6AHIC CATALYZERS 



There is no evidence at present that germinal pre- 

 dispositions of proportion are influenced by the hor- 

 mones and chalones which from the above observa- 

 tions are shown to exert so profound an influence on 

 bodily proportions. This can be tested only by very 

 careful experimental work. One reason for believing 

 that the heredity germ may be influenced in this 

 manner is that it is the germinal or chromatin material 

 of the body cells which responds to these organic 

 catalyzers, as shown in the transplantation experi- 

 ments of the placing of the ovary into the male body 

 and the testes into the female body, which results in 

 the internal secretions from these glands evoking the 

 male characteristics in the chromatin of the female 

 body cells and female characteristics in the chromatin 

 of the male body cells. 



These latent characters can reside only in the germ 

 chromatin. Consequently in the germ chromatin of 

 the germ cells proper there may be possible influences 

 of interaction awaiting discovery through experiment. 

 Such discovery would lend support to the tetrakinetic 

 theory. 



SUMMARY OF THEORETIC CAUSES OF EVOLUTION 



EVIDENCE AGAINST THE LAMARCKIAN PRINCIPLE 



The balance of evidence in titanothere evolution is 

 decidedly against the Lamarckian principle of the in- 

 heritance of acquired characters, which was so strongly 

 advocated, from paleontologic and mechanical data, 

 by Cope. Neither the mode of initiation of allome- 

 trons nor that of rectigradations, when carefully ana- 

 lyzed, appears to sustain this principle. Though it is 

 a convenient explanation of the development and 

 degeneration of certain organs it does not account for 

 all origins nor for most of the adaptations of pro- 

 portion. 



EVIDENCE AGAINST THE THEORY OF SELECTION OF 

 MINUTE VARIATIONS 



The evidence is also strongly against Darwin's 

 hypothesis of the selection of minute variations as of 

 survival value. The chief counter evidence is that 

 new characters (rectigradations) and new propor- 

 tions (allometrons) do not arise by chance but from 

 some undiscovered definite orthogenetic principle that 

 affects the germ. 



EVIDENCE FAVORABLE TO THE SELECTION OF CERTAIN 

 FLUCTUATIONS 



The Darwinian principle, on the other hand, afi^ords 

 the most reasonable hypothesis we have to offer at 

 present of the evolution of those larger proportions 



that have a distinct survival value — for example, the 

 length of neck of the giraffe, the length of limbs of 

 the unborn colt. Acceleration of adult limb propor- 

 tions into fetal stages, to protect the young at birth, 

 affords the best example of the survival value of 

 germinal fluctuating characters and the strongest 

 refutation of the Lamarckian hypothesis. 



UNKNOWN CAUSES OF THE ORIGIN OF RECTIGRADATIONS 



We are wholly at a loss to advance any explanation 

 of the causes of rectigradations, of the orthogenetic 

 appearance of horn rudiments on the head, or of 

 cuspules on the teeth. Although these new characters 

 arise independently in different phyla, thus pointing 

 to some kind of germinal predetermination or pre- 

 disposition, they do not indicate an internal perfecting 

 tendency, because they are timed with reference to 

 external-internal reactions. Consequently there ap- 

 pears to be some kind of interaction between environ- 



, ■>. fiAy/a 



Figure 756. — Theoretic selection of fluctua- 

 tions of proportion 



Gradual shifting of proportions (d, c, be, b, as of length of 

 neck) in successive generations. Showing the shifting of 

 the fluctuations of frequency in a series of characters (a-e). 

 In a lower geologic stage (A) d is the most frequent char- 

 acter; in the next higher geologic stage (B) c is the most 

 frequent character; in the next higher stage (C) 6c is the 

 most frequent character; in the highest stage (D) b is the 

 most frequent character. This shitting is consistent with 

 the Lamarckian, the Darwinian, or the tetrakinetic theory. 



ment, habit, and the time of appearance of these new 

 organs; but we have no inkling as to what this rela- 

 tion is — whether, in fact, it is causal unless it consists, 

 of some kind of physico-chemical interaction. 



NECESSITY OF EXPERIMENT ON THE TETRAKINETIC 

 PRINCIPLE 



The tetrakinetic principle is a working hypothesis or 

 line of suggestion as to a possible relation between the 

 external energies of the environment and the body 

 and the internal energies of the development and 

 evolution of the germ. That some such causal rela- 

 tion exists is faintly indicated by the modes of evolu- 

 tion both of rectigradations and of certain propor- 

 tions. As there are certain energizers in the body, 

 catalytic messengers that hasten the development of 

 one organ and retard the development of another, we 

 may now obtain a glimpse of what may possibly 



