46 ESSAYS OF A BIOLOGIST 



do what the worker or the queen can do. A muscle- 

 cell, because it has gained the power to contract, 

 is cut off from other possibilities ; it cannot secrete, 

 or digest, or carry messages. The aggregate of 

 nerve-cells which makes the physical basis of mind 

 is held fixed to its post, incapable of turning to other 

 functions. 



It follows that the units of all such aggregates 

 are subordinate to the whole — they have lost their 

 independence, and can often no longer be considered 

 as individuals at all, except historically. But in man, 

 none of these things hold. A man can for half his 

 day be the merest cog, subordinate in every detail 

 of his action to the needs of the community, but for 

 the other half be himself, a full and complete individu- 

 ality, making the community serve his own ends and 

 needs. For him, aggregation does not mean complete 

 and irreversible subordination ; his specialization is 

 reversible, and indeed his potentialities as an individual 

 actually increase with the increased individuality of 

 the aggregate to which he belongs. 



Bearing these differences in mind, we may turn 

 to consider how our doctrine of progress helps us in 

 studying humanity. 



At the outset we must guard ourselves against the 

 idea that human society has reached any high level 

 of biological individuation. I may perhaps quote 

 from what I have written elsewhere : * If we were 

 to draw a parallel between primitive types of society 



