14 ORGANIC EVOLUTION 



and ninety-nine, all but one, are destined, on the average, 

 to die, even assuming that the parent plant dies, which is 

 by no means always the case. Very many of our flower- 

 ing plants form more seeds than this annually, yet their 

 numbers do not materially increase under ordinary con- 

 ditions. 



Fern spores are much more numerous than the seeds 

 of flowering plants, and the lower cryptogams, the Fungi, 

 especially the Bacteria, breed with a rapidity which is far 

 beyond our comprehension. Under favorable conditions 

 a single bacterium might produce a million bacteria in a 

 day. If this rate of increase should continue, we would 

 have at the end of a week a million million million million 

 million million million bacteria, all derived from the single 

 individual with which we started. 



If all living things tend to reproduce with such aston- 

 ishing rapidity, and yet we find that their numbers do not 

 materially increase, but remain about constant, what is it 

 that holds them in check ? What kills the excess ? Many 

 things, unfavorable conditions of all sorts. Starvation 

 claims probably the largest share of victims ; heat and cold 

 kill many; floods, drouth, and storms destroy others ; multi- 

 tudes perish to feed their enemies ; disease takes its share. 

 Nature is fertile in expedients for killing. Life is not 

 easy. Success is not the rule but the rare exception. 

 For every one which lives and succeeds in rearing off- 

 spring, thousands and thousands perish. Competition is so 

 keen that no unhealthy or imperfect individual can endure 

 it. The weak fall first, leaving the field to their stronger 

 brethren, who in turn fight it out among themselves, till 

 finally only the strongest and finest survive. In a struggle 



