152 THE EVOLUTION OF MAN. 



and so on. In short, the ever-increasing division of laboui 

 specializes the people into various ranks or castes, which 

 always tend to become more sharply defined in propor- 

 tion as the state becomes more highly developed: all 

 follow diverse occupations, and yet work for a common end. 

 In this way, from the descendants of a single human pair, 

 a simple community of individuals, originally alike, first 

 gradually arises, and this is followed by a more or less 

 well-organized confederation. In this community, we may 

 regard the more or less complete division of labour among 

 individuals, or the so-called specialization, as the standard 

 by which the grade of development of its culture may be 

 measured. 



A process similar to this, and the details of which each 

 can easily fill up for himself, took place millions of years 

 ago, when, at the beginning of organic life on the earth, 

 one-celled organisms at first developed, and were afterwards 

 followed by many-celled forms. 



The single cells which arose by reproduction from the 

 oldest parent-cells must at first have lived in an isolated 

 condition ; each one performed the same simple offices as 

 all the others; they were satisfied with self-preservation, 

 nutrition, and reproduction. At a later period isolated 

 cells gathered into communities. Groups of simple cells, 

 which had arisen by the continued division of a single 

 cell, remained together, and now began gradually to perform 

 different offices in life. The first traces of specialization, or 

 division of labour, soon occurred, as one cell assumed one 

 office, another another. One set of cells may have devoted 

 themselves especially to the absorption of food, or nutrition; 

 other cells may have busied themselves only with repro- 



