Februabt 11, 1910] 



■SCIENCE 



205 



More familiar is that class of adjust- 

 ments by means of which, through use of 

 a part, its functional activity becomes more 

 effective; the muscle grows strong, the 

 skin thickens, the iris contracts and even 

 the bones bear witness to stresses and 

 strains. Here also we are beginning to 

 see that these adjustments may be noth- 

 ing more than extensions of the normal 

 processes of growth— function breeds func- 

 tion, because the very act of functioning 

 is itself a step towards further change in 

 the same direction. 



One of the most remarkable adaptations 

 is the development of a whole embryo out 

 of half of an egg. But here, too, we have 

 come to see that the result is not due to 

 any special and sudden development of a 

 new and wonderful power, but that the 

 regulative process is a simple expression 

 of the same processes that are at work in 

 normal development. The marvel is no 

 more, no less, than that of development 

 itself. 



These four great groups include many 

 of the most important kinds of adaptive 

 responses shown by organisms. We can 

 not afford, I think, to underestimate their 

 importance. But observe! They all con- 

 cern the individual; they tell us nothing 

 in regard to the next generation. Yet 

 even here there has been slowly accumu- 

 lating in recent years evidence to show 

 that some of the external agents that af- 

 fect the soma or body of the individual 

 may affect the eggs in the ovary of that 

 individual in exactly the same way. 



This evidence fails, however, to show 

 that it is the adaptive responses only that 

 take place alike in germ and soma. The 

 evidence indicates at most that certain 

 kinds of external factors may affect soma 

 and germ in the same way, and that these 

 effects apply equally to beneficial, indif- 

 ferent and baleful results. There is no 



satisfactory evidence in favor of the view 

 that specific structures produced first in 

 the soma can be transmitted from soma to 

 germ ; and least of all is there any evidence 

 that the eggs or the sperms are affected by 

 the psychic experiences of the body. Yet 

 it is this latter idea to which the Lamarek- 

 ian school has so often appealed. In re- 

 cent times the Lamarckian has played a 

 losing game. He has been driven from 

 pillar to post and failed to make good 

 many of his claims, which, if true, should 

 furnish the fairest opportunity for demon- 

 stration that the whole field of adaptation 

 has to offer. 



We find in this connection a significant 

 fact. Nature has not hesitated to insert 

 an unspeeialized egg and sperm between 

 every link in the evolutionary series. She 

 seems more concerned in transmitting a 

 material sensitive to external responses 

 than the effects of previous responses them- 

 selves. 



We are now in a position to attack what 

 is generally conceded to be the central 

 problem of adaptation. It is held that the 

 crucial test of any theory of adaptation is 

 found in those cases where special contri- 

 vances exist, that could not have arisen 

 through action and reaction in a causal 

 sense: for example, in many insects the 

 male and female organs of copulation 

 show close adjustments to each other; 

 those of the male having parts that fit 

 precisely corresponding parts of the fe- 

 male. These fittings vary from species to 

 species, and a change in the male finds a 

 corresponding change in the female of the 

 same species. I shall call these lock and 

 key adaptations — structures and functions 

 complete at birth of the organism. It is a 

 consideration of these adaptations that has 

 separated the naturalists as a class from 

 the physiologists, and has drawn the nat- 



