426 THE STUDY OF ANIMAL LIFE CHAP. 



Ideological interpretation. His greatest work, however, 

 is of a less popular character, namely, the Generelle 

 Morphologic (2 vols., Berlin, 1866), which in its reasoned 

 orderliness and clear generalisations ranks beside Spencer's 

 Principles oj Biology. 



THOMAS HENRY HUXLEY (1825-1895) was one of the 

 first to stand by Darwin, and to wield a sharp intellectual 

 sword in defence and attack. No one fought for the 

 doctrine of descent in itself and in its consequences with 

 more keenness and success than the author of Man's 

 Place in Nature (1863), American Addresses, Lay Sermons, 

 etc., and no one championed the theory of natural selec- 

 tion with mere confident consistency or with more skil- 

 fully handled weapons. 



8. Steps of Progress since Darwin's Day. As Alfred 

 Russel Wallace said in the preface to his Darwinism 

 (1889) : ' Descent with modification is now universally 

 accepted as the order of nature in the organic world." 

 But while this remains true, there is anything but 

 unanimity in regard to the way in which the ascent of 

 life has come about, as to the working of the nature-loom. 

 Naturalists are not within sight of any complete theory 

 of the factors in organic evolution. 



In regard to variations, the raw materials of evolution, 

 some notable steps of progress have been made since 

 Darwin's day. (1) Patient accumulation cf facts has 

 shown that variations are even more abundant than 

 Darwin supposed. The fountain of change is inexhaus- 

 tible. (2) The registration or plotting out of observed 

 quantitative variations has shown that they usually 

 form what is called the Curve of the Frequency of Error. 

 There is a proportion between the frequency of a particu- 

 lar change, e.g. gigantic or dwarfish stature, and the 

 amount of its departure from the mean of the character 

 in question. (3) More evidence has been forthcoming 

 of what Darwin called the ' correlation of variations." 

 That is to say, a number of changes in an organism 

 are often linked together, being different expression 

 of some single deeper change. (4) Discontinuous or 

 brusque variations are much more frequent than Darwin 



