490 POPULAR SCIENCE MONTHLY. 



larger, and more space must be given up to coal, and tliis dimin- 

 ishes tlie remaining accommodation. 



" Evolution may produce an altogether new type of vessel that 

 shall be more efficient than the old one, but when a particular 

 type has become adapted to its functions, through long experience, 

 it is not possible to produce a mere variety of its type that shall 

 have increased efficiency in some one particular without detri- 

 ment to the rest. So it is with animals." 



This quotation from Galton shows how a type may be estab- 

 lished by selection, and it also shows why it is not possible to 

 make any great and permanent change in the type of one charac- 

 teristic of an organism unless changes at the same time occur in 

 the type of other characters of the same organism. It also fol- 

 lows that a breeder of domesticated animals or cultivated plants 

 who devotes his attention to one characteristic exclusively must 

 soon reach a point where no further improvement in this quality 

 is practicable unless the spceies is at the same time modified in 

 other respects. This fact does not prove that specific stability is 

 due to anything else than selection. It only proves that no great 

 change is possible without the co-ordinated modification of corre- 

 lated features, and this is just what we should expect as the effect 

 of long ages of selection. 



The passage I have quoted from Galton seems to indicate that, 

 after all, he may believe that the specific types of zoology and 

 botany are nothing more than the persistent effects of past selec- 

 tion, and that his statement that " organic stability is independ- 

 ent of selection " may refer to present selection only. 



These statements are clear and explicit, however, and they 

 have been interpreted by most readers as a flat contradiction of 

 the view that the mechanism which leads to the formation of new 

 types is identical, on its vital side, with that which preserves estab- 

 lished types ; the view that the differences between the two are 

 differences in the external world. 



He says (Nature, September 4, 1885) : " It is some years since I 

 made an extensive series of experiments in the produce of seeds of 

 different sizes, but of the same species, ... It appears from these 

 experiments that the offspring did not tend to resemble their par- 

 ent seeds in size, but to be always more mediocre than they ; to 

 be smaller than they if the parents were large ; to be larger than 

 the parents if the parents were very small," and that the analysis 

 of the family records of heights of 205 human parents and 930 

 children fully confirms and goes far beyond the conclusions ob- 

 tained from seeds, as it gives with great precision and unexpected 

 coherence the numerical value of the regression toward medi- 

 ocrity. He says that this regression is a necessary result of the 

 fact that " the child inherits partly from his parents, partly from 



