October 3, 1913] 



SCIENCE 



465 



ation lurks in the plain statement that by 

 ruthless elimination a black flock of pig- 

 eons can be produced, even that thereby the 

 individuals have been made black. (But of 

 course the breeder has thereby not invented 

 the black pigment.) 



There can be no evolution, progress, 

 without response to stimulus, be this en- 

 vironmental or constitutional, i. e., depend- 

 ing upon the composition and the corre- 

 lated working of the various parts within 

 the organism. Natural selection has but to 

 favor this plasticity, by cutting out the 

 non-yielding material, and through in- 

 heritance the adaptive material will be 

 brought to such a state of plasticity that it 

 is ready to yield to the spur of the moment, 

 and the foundation of the same new organs 

 will thereby be laid, whenever the same 

 necessity calls for them. Here is a di- 

 lemma. On the one hand the organism 

 benefits from the ancestral experience, on 

 the other there applies to it de Rosa's law 

 of the reduction of variability, which nar- 

 rows the chances of change into fewer di- 

 rections. But in these few the changes will 

 proceed all the quicker and farther. Thus 

 progress is assured, even hypertely, which 

 may be rendered by "overdoing a good 

 thing. ' ' 



Progress really proceeds by mutations, 

 spoken of before, orthogenesis, and it would 

 take place without selection and without 

 necessarily benefiting the organism. It 

 would be mere presumption that the seven- 

 gilled shark is worse off than its six- or 

 five-gilled relations ; or to imagine that the 

 newt with double trunk-veins suffers from 

 this arrangement, which morphologically is 

 undoubtedly inferior to the unpaired, 

 azygous, etc., modifications. The fact that 

 newts exist is proof that they are efficient 

 in their way. Such orthogenetic changes 

 are as predictable in their results as the 

 river which tends to shorten its course to 



the direct line from its head waters to the 

 sea. That is, the river's entelechy is no 

 more due to purpose or design than is the 

 series of improvements from the many gill- 

 bearing partitions of a shark to the fewer, 

 and more highly finished comb-shaped gills 

 of a Teleostean fish. 



The success of adaptation, as measured 

 by the morphological grade of perfection 

 reached by an organ, seems to depend upon 

 the phyletic age of the animal when it was 

 first subjected to these "temptations." 

 The younger the group, the higher is likely 

 to be the perfection of an organic system, 

 organ or detail. This is not a platitude. 

 The perfection attained does not depend 

 merely upon the length of time available 

 for the evolution of an organ. A recent 

 Teleostean has had an infinitely longer time 

 as a fish than a reptile, and this had a 

 longer time than a mammal, and yet the 

 same problem is solved in a neater, we 

 might say in a more scientifically correct 

 way by a mammal than by a reptile, and 

 the reptile in turn shows an advance in 

 every detail in comparison with an am- 

 phibian, and so forth. 



A few examples will suffice: 



The claws of reptiles and those of mam- 

 mals ; there are none in the amphibians, al- 

 though some seem to want them badly, like 

 the African frog Gampsosteonyx, but its 

 cat-like claws, instead of being horny 

 sheaths, are made out of the sharpened 

 phalangeal bones which perforate the skin. 



The simple contrivance of the rhinocero- 

 tic horn, introduced in Oligocene times, 

 compared with the antlers of Miocene Ger- 

 vicornia and these with the response made 

 by the latest of Ruminants, the hollow- 

 horned antelopes and cattle. The heel- 

 joint; unless still generalized, it tends to 

 become intertarsal (attempted in some liz- 

 ards, pronounced in some dinosaurs and in 

 the birds) by fusion of the bones of the 



