NATURAL SELECTION 13 



have a yearly birth-rate at least as great as that of the 

 more prolific birds. Frogs and other Amphibia have an 

 immensely larger number of young each season, often 

 several hundred for each pair. Many of the fishes lay 

 half a million eggs for each mature female, so that here 

 we have an example of a yearly death-rate two hundred 

 and fifty thousand times as great as the permanent popu- 

 lation, since on the average only one male and one female 

 out of this half-million of young survive to take the place 

 of their parents and keep the number of individuals in the 

 species up to its usual mark. A starfish may lay a million 

 eggs each season, and, as the number of adult starfish 

 remains about constant from year to year, we see that for 

 every starfish living nearly half a million die each year. 

 The birth-rate among the Mollusca, worms, jellyfish, 

 sponges, and the Protozoa, like that of the starfish, is 

 enormous. Taking animals as a whole, it would be safe 

 to say that hundreds of thousands die every year for each 

 one that lives. 



% 



Among plants the figures are no less startling. The 

 higher flowering plants reproduce much more slowly than 

 most of the lower plants, yet among them the death-rate 

 is very large. The common marguerite daisy, which 

 grows so abundantly in eastern America, is a fair ex- 

 ample. It is a moderate estimate to say that one of 

 these daisies of ordinary size, blooming as it does for 

 about two months, would have one hundred and twenty- 

 five heads of bloom each year. Each head of blossoms 

 would have about five hundred seeds, making a total of 

 sixty-two thousand five hundred seeds for each plant each 

 year. Of this number sixty-two thousand four hundred 



