44 SYMBIOGENESIS 



We are not justified, moreover despite all these striking 

 temporary benefits in viewing the case of Convoluta as 

 approaching a genuine biological symbiosis, but it rather 

 seems to be a reversion from such. To take a true instance of 

 symbiogenesis : I have shown in a previous volume (Evolution 

 by Co-operation) that there is a significant connection between 

 the considerable longevity of certain trees or shrubs a factor 

 generally connected with a relatively high amount of repro- 

 ductive expenditure and the peculiar adequacy of their 

 productions ("love-foods ") for the higher animals 

 characterised in turn by their long periods of gestation and 

 likewise by their readiness to cultivate and propagate their 

 food-plants. On this symbiogenetic relation I shall have more 

 to say later on. 



Protracted gestation, longevity, symbiotic behaviour, 

 mutual aid, and mutual toleration with security of life, high 

 status, and general productiveness thus always go together in 

 genuine biological symbiosis, as they do in the domestic 

 symbiosis between the parts of a green plant. Hence genuine 

 biological complements are like the parts of a green plant 

 economically and physiologically belonging to one another, 

 although physically separate. This it is vital to remember as 

 the true relatedness thus disclosed constitutes in great part the 

 mechanism of heredity. 



I have at the same time been urging in a general way the 

 significance of the cumulative effects of food upon the genera- 

 tive system, and now that the connection of nutrition with 

 every important biological development is becoming increas- 

 ingly apparent, it is well to elucidate still further this very 

 important matter. 



The comparative harmony and order of the reproductive 

 life of the Mammalia, as is well known, are purchased by a 

 considerable amount of reproductive expenditure. It requires 

 the discharge of manifold and exacting duties and presents a 

 case of noblesse oblige. And in this instance we can see how 

 higher symbiotic needs have called forth new organs, and how 



