GENETICS 137 



dominance, although frequently it may be the opposite 

 of Mendelian " dominance," and rather to be found among 

 the few and inconspicuous " recessives." 



The fact that all strenuous organisms are directly involved 

 in simultaneous progressive changes has arisen, as we have 

 seen, from definite bio-economic necessities. The first 

 necessities we found to be symbiotic necessities, i.e., necessities 

 of mutual labour and mutual diversification, i.e., reciprocal 

 differentiation. Without a fulfilment of these necessities there 

 can be but a relatively insignificant production of values. It 

 is not too much to say that in reality no single cell has ever 

 been fertilised without the previous performance (by 

 progenitors) of a series of symbiotic acts, as it is idle to 

 suppose that without a previous production of values, repro- 

 duction can have any real biological importance, i.e., every 

 successive generation is subject to the same stress of circum- 

 stances, and must by its reaction thereto contribute its quota 

 along the general line of development. 



As we have already seen, with the multiplication of values 

 and of individuals, symbiotic and colonising principles come 

 early into operation. I have emphasised in my preface to 

 Evolution by Co-operation how Robert Chambers' sagacity 

 clearly perceived that though the "fecundity of nature" be 

 such as to cause organisms in time to press upon the verge of 

 the local means of subsistence, there is, on the other hand, a 

 colonising principle which comes into play to meet the con- 

 tingency of over-population. In other words, pressure of 

 population results in new specialisations, new capacities, new 

 values, and, concomitantly, in new forms and degrees of bio- 

 logical antagonism, according to the new forms and degrees of 

 biological relatedness now arising. 



That the principle of diversification is more profoundly 

 effective than was hitherto supposed, we may gauge from the 

 fact that according to recent biological observations no two 

 cells are ever alike. Their dissimilarity, I should say, has 

 reference in great part to the ever-changing bio-economic and 



