DESCENT WITH CHANGE 375 



transform the materials of its environment into Paramecium proto- 

 plasm — at the rate of 3000 generations in five years. And all the 

 descendants (if they actually existed) would equal 2 raised to the 

 3000th power, or a volume of protoplasm approximately equal to 

 10 1000 times the volume of the Earth! The Plant Lice, or Aphids, 

 may produce a dozen generations in a year. The final brood, as- 

 suming the average number of young produced by each female to 

 be one hundred and that every individual produced its full com- 

 plement of young, would consist of ten sextillion individuals — 

 a procession, if it could be marshalled, that "would extend from 

 the Earth out into space far beyond the furthest star that has 

 ever been discerned by the telescope." The common House Fly 

 under favorable conditions may lay as many as six batches of eggs, 

 of about one hundred and forty eggs each, during its short life 

 of approximately three weeks. Assuming that all the progeny 

 survived and multiplied at the same rate, ''the progeny of a single 

 pair, if pressed together into a single mass, would occupy some- 

 thing like a quarter of a million cubic feet, allowing 200,000 flies to 

 a cubic foot." And the all too familiar Mosquito may have nearly 

 two hundred billion descendants during one summer. Indeed, the 

 common Rat will afford astounding figures. (Figs. 222, 246, 258.) 



The number of individual organisms on the Earth is essentially 

 infinite. If it is assumed that the average life span of an individual 

 is a year — a day would probably be nearer the truth — then 

 one must grip the fact that this infinitude of individuals is each 

 year wiped out, and replaced by reproduction. Such an almost 

 explosive expansion of a population under favorable conditions is 

 appalling, though true, and serves to afford an appreciation of 

 the enormous realized and unrealized potentialities of living mat- 

 ter to make more living matter — to reproduce. ' The problem 

 of organic evolution is that of the evolution of an organic mass 

 consisting of an infinitude of individuals reproduced during an 

 infinitude of generations." 



Something must — does — suppress the inherent power of each 

 species to overpopulate the Earth, and Darwin emphasized the 

 struggle for existence between the individuals of species. 

 Since the struggle is so keen, a variation, however slight, which 

 fits — adapts — an individual better to its surroundings than its 

 neighbors are adapted, will, more often than not, give its possessor 

 an advantage in the struggle, and accordingly the latter will 



