RELATION OF SOCIOLOGY TO BIOLOGY. 329 



the social body. They ought to cooperate for the welfare of the 

 whole, 



2. Eoolution. — All the laws of evolution which have been discovered 

 in organisms apply also to society, but with certain limitations, which I 

 believe are very significant. 



{a.) Laio of Differentiation. — Tlie most fundamental law of evolu- 

 tion is differentiation. The organism, as I have described it above, 

 with its cells of diverse forms and functions, was not thus constituted 

 in the beginning of its existence, but gradually became so by a process 

 of diflferentiation. In the early stages of an organism the constituent 

 cells are all alike in form, and each performs, though imperfectly, all the 

 functions necessary in this early stage. But, as the organism develops, 

 the cells begin to take on different forms, and to perform different func- 

 tions, and this process of differentiation continues until, in the mature 

 condition of the highest organisms, each group of cells (or each organ) 

 is limited to the performance of one function only. This one function 

 is its only evidence of life. Now, concurrently with this increasing 

 differentiation of form and limitation of function, there is, of necessity-, 

 an increasing mutual dependence of parts, and a sacrifice of the inde- 

 pendent life of the part to the common life of the whole. In the low- 

 est condition of the organism, where the cells are all alike, and each 

 performs, though imperfectly, all the functions, there is a very con- 

 siderable, sometimes a complete, independent life in each cell ; so that 

 it may be separated without injury either to itself or to the community 

 of cells : the independent life is large, the common life is feeble. But, 

 as we rise in the scale of organization, the independent life of the part 

 is merged more and more into the general life of the whole — is sacri- 

 ficed, and goes to make up the common life — until, in the mature con- 

 dition of the highest organisms, the independent life of the constituents 

 is reduced to a minimum, while the common life is advanced to a maxi- 

 mum. This complete merging of the independent life of the part into 

 the common life — this identification of life with function — is the ideal 

 of the animal organism : the nearer it approaches this condition the 

 higher manifestly is the organism. 



Or take instead that larger organism, more nearly i-esembling, and 

 therefore better illustrating, the social organism, viz., the lohole organic 

 Jcingdom, — its present diverse condition has been reached also only by 

 a process of differentiation. Commencing in the earliest times, with 

 similar and independent beings, by a continual process of separation 

 and differentiation, animal forms have become more and more diverse, 

 occupying different places and performing different functions in the 

 economy of Nature ; the higher becoming still higher, and the lower 

 becoming lower ; the mutual dependence and interaction of all parts 

 becoming greater and greater, until the ideal seems almost reached in 

 the present fauna and flora. If we can conceive any organism still 

 higher than man, or lower than the monera — if we can conceive a re- 



