INTRODUCTORY 7 



Organic Evolution. It is one thing to state that Birds evolved from 

 an extinct stock of Reptiles; it is another thing to try to indicate, 

 by analogy from the present day, what factors were at work in 

 this notable emergence which took place millions of years ago. 

 Etiology is an inquiry into the causes of phylogeny, or the origin 

 of races, but it must be based on the observational and experimental 

 study of present-day variation and heredity, selection and isolation. 

 Account must be taken of the plasticity of living creatures in the 

 hands of their environment, of the shufflings of the hereditary cards 

 during the maturation and fertilisation of the germ-cells, and also 

 of the factors that come into play in the early stages of development. 

 Here have to be discussed the particular theories of evolution that 

 are associated with Lamarck, Darwin, Weismann, and their suc- 

 cessors. Thus a large section of the book is entitled Evolution- 

 Theory; for that is what Etiology comes to. 



So far, then, a logical plan: Ecology and Physiology, Taxonomy 

 and Morphology, Embryology and Palaeontology, and then all the 

 problems of Etiology. It will be understood, of course, that these 

 logical sections are not to be regarded as pigeon-holes with rigid 

 walls; for the organism is a unity whose various aspects cannot be 

 separated off except for purposes of convenience. Thus the con- 

 sideration of a function necessarily raises the question of the struc- 

 tural arrangements by which it is carried out; and the anatomical 

 analysis of an organ necessarily raises the question of the utility 

 of the several parts. Similarly, the evolution-question: "By 

 what steps and by what factors did this come to be as it is?" 

 must be behind or beneath all the other inquiries, whether 

 anatomical or physiological, whether dealing with embryos or 

 with fossils. 



Our book contains tentative answers to four great questions. Of 

 these the first asks how Biology stands among the other sciences, 

 how it is related to Chemistry and Physics 'below it, and to Psych- 

 ology and Sociology above it. What is the most convenient grouping 

 of the sciences, and how are they distinguished in their methods 

 and categories? Here, more profitably than at the outset, the 

 question: What is Life? has to be considered; and the long-standing " 

 controversy between the mechanists and the vitalists, whose 

 descriptions are complementary rather than antithetic. 



Then comes the question of Man's place in Nature, his apartness 

 from the animal kingdom, and yet his solidarity with it ; his vaguely 

 discerned pedigree, and the factors in his ascent. This leads on to 

 an indication of the biological contributions to Sociology. 



From this it is natural to pass to the applications of Biology to 

 the furtherance of Man's welfare. How has Biology contributed to 

 the progress of Agriculture and Fisheries, Medicine and Hygiene? 

 And how far are biological methods and results of value in regard 



