130 CONDITIONS AFFECTING THE 



In the woods of Florida there are a great many pigs, 

 and it is a very curious thing that they are all black, 

 every one of them. Professor Wyman was there some 

 years ago, and on noticing no pigs but these black 

 ones, he asked some of the people how it was that they 

 had no white pigs, and the reply was that in the 

 woods of Florida there was a root which they called 

 the Paint Root, and that if the white pigs were to 

 eat anv of it, it had the effect of making their hoofs 

 crack, and they died, but if the black pigs eat any of 

 it, it did not hurt them at all. Here was a very simple 

 case of natural selection. A skilful breeder could not 

 more carefully develope the black breed of pigs, and 

 weed out all the white pigs, than the Paint Root 

 does. 



To show you how remarkably indirect may be such 

 natural selective agencies as I have referred to, I will 

 conclude by noticing a case mentioned by Mr. Darwin, 

 and which is certainly one of the most curious of its kind. 

 It is that of the Humble Bee. It has been noticed 

 that there are a great many more humble bees in the 

 neighbourhood of towns, than out in the open country ; 

 and the explanation of the matter is this : the humble 

 bees build nests, in which they store their honey and 

 deposit the larvae and eggs. The field mice are amaz- 

 ingly fond of the honey and larvse; therefore, wherever 

 there are plenty of field mice, as in the country, the 

 humble bees are kept down ; but in the neighbourhood 

 of towns, the number of cats which prowl about the 

 fields eat up the field mice, and of course the more 

 mice they eat up the less there are to prey upon the 

 larvae of the bees — the cats are therefore the indirect 



