412 THE GRAMMAR OF SCIENCE 



§ lo. — The Unsolved Problems 



That the types of Hving forms are changing can 

 hardly be doubted by any one who has dealt statistically 

 with large numbers of individuals in the same and in allied 

 local races. There is undoubtedly a selective death-rate, and 

 we have means of quantitatively determining its value, but 

 the questions we have to answer are not entirely answered 

 by finding this value. We want to know further — 



(i.) Whether the changes are secular or merely periodic ? 



(ii.) Whether the changes, if secular, are capable of 

 differentiating one form of life into two, so far removed 

 from each other as to be absolutely or relatively infertile, 

 i.e. are capable of giving an account of the origin of 

 species ? 



(iii.) Whether the changes, if secular and differential, 

 are sufficiently rapid, or could in the past have been 

 sufficiently rapid, to account for the origin from some one 

 simple form of the great variety of living forms we are 

 acquainted with ? 



Let us consider these questions for a little, although in 

 doing so we may have to anticipate some of the matters 

 to be more fully discussed in the following chapter. If 

 we are given an adult local race and find the frequency 

 distribution of any organ, say at the beginning of adoles- 

 cence, this distribution will probably, almost certainly, 

 have changed, selection will have taken place, if we 

 determine it again, say during the period of reproduction. 

 A selection of the adolescent generation may be the 

 parents of the next generation, and this generation when 

 adolescent might have the same frequency distribution as 

 the previous adolescent generation. In other words, 

 selection does not necessarily mean a permanent or pro- 

 gressive change in the type. We may demonstrate that 

 environment does select, but yet this selection may be 

 purely periodic and suffice only to maintain the race 

 where it is. Each new adolescent generation is not the 

 product of the entire preceding adolescent generation, but 



