26 THE GROWTH OF GROUPS 



and the conditions suitable. We are able to believe that 

 a thousand animals of a kind may grow to be a million, 

 but unable to believe that one may grow into a thousand. 

 To explain the increase of a specific group after it has 

 become established is considered easy, but to explain 

 how the group became established is regarded as a different 

 problem, which for many biologists has been solved 

 by the theory of Natural Selection. It seems to be a 

 tenet of the theory that there are two processes in the 

 history of a species, that the origin is a process distinct 

 from any subsequent expansion or contraction which it 

 may subsequently undergo. Although, according to the 

 theory, the action of selection never ceases, yet its visible 

 effect on the species comes to an end as soon as the species 

 has arrived. The date of arrival may be long ago, 

 as in the extreme case of Lingula, an animal form which 

 is common to-day in some part of the world, and has been 

 preserved practically unchanged since the commencement 

 of the record of fossils. 



As opposed to this view, the following propositions 

 will be made : 



1. There are not two processes in the history of a 

 group, but only one, a process of expansion and contrac- 

 tion. The moment of arrival of a group, if it is to become 

 a group, is when the first member of it is born. 



2. All limitation as to the numbers of individuals 

 composing a specific group should be removed from our 

 conception of such a group. We place no limit on the 

 greatness of the number, neither should we limit the 

 smallness of the number. 



3. The growth of a group is comparable to its extinc- 

 tion ; just as the extinction of a group is brought about 



