NORMAL GROWTH AN ADAPTATION 13 



ment Some plants grow tougher and more firmly rooted when 

 exposed to strong winds ; but throughout the vegetable kingdom 

 the faculty, if present at all, is developed only in the slightest 

 degree. At present, however, we need not labour this question of 

 the evolution of the power of growing in response to use. We 

 shall be in possession of much more definite and decisive evidence, 

 especially when we consider mind. 



24. In brief the notion that the power of growing, especially of 

 growing adaptively, under the stimulus of use, is present in all 

 living tissues, is merely a vague guess founded on popular observa- 

 tion of our familiar human development. There is no veil like the 

 veil of familiarity. Never yet has this question been made the subject 

 of close and accurate investigation. Since some human structures 

 develop in this way, it has been assumed that all structures in all 

 animals and plants can, and do, so develop. Like many other 

 popular guesses it has been accepted quite without question even by 

 thinkers in science. Vast systems of philosophy have been built 

 on it and acclaimed as the highest products of human wisdom. 

 But it is very doubtful whether any other error in the whole range 

 of biology, indeed of scientific thought, has been productive of 

 more confusion, futile discussion and practical mischief. My 

 language is strong, but the reader will find it fully justified. 1 



25. Obviously, then, powers of developing in response to 

 definite stimuli are, in the case of all species, delicate adjustments 

 to the environment. If any individual varies from the ancestry so 

 as to lose this adjustment, this power of responding by growth in 

 definite ways to definite stimuli, he fails to develop the right char- 

 acters to the right extent and perishes. Every type of plant and 

 animal, the lichen, the beetle, and the man, for example, fits its 

 own niche in nature as the hand does the glove ; but it fits only 

 because its germ-plasm has been so fashioned by evolution that 

 every normal individual grows into adaptation to his environment 

 in response to stimuli. 



26. Speaking generally, all growth is either immediately 

 adaptive or is a provision for future adaptation. Thus human 

 germ-cells are adapted by their structures and capacities for exist- 

 ence in the testes and ovaries. Under the stimulus of nutriment 

 they develop into embryos and thus are able to fit the next 

 environment, the uterus. Here they continue to develop till they 

 grow into fitness for life in the mother's arms. Thereafter, use and 

 injury come into play ; and, with some characters developing under 



1 See*chapter iv. 



