ORGANIC EVOLUTION 



I. THE THEORY 



NATURAL SELECTION 

 Heredity. 



Every one knows that among both animals and plants 

 the offspring tend to resemble their parents. The young 

 of a horse is always a horse and never a zebra. Wolves do 

 not give birth to foxes. Sunflowers will not grow from 

 thistle seed. Each kind of animal and plant breeds true, 

 as we say. This was not always recognized, as is illustrated 

 by the ancient Greek conceptions of the origin of animals 

 from plants, not only supposed to have taken place in the 

 original creation of animals, but also thought to be of con- 

 tinued occasional occurrence. Similarly, the belief, preva- 

 lent during the Middle Ages, that the goose-barnacle (a 

 kind of crustacean, Fig. i) transforms into the barnacle- 

 goose (Fig. 2) is an indication that at that time the inde- 

 pendence of different species was not so clearly recognized 

 as now. Sylvester Giraldus, in his Relations concerning 

 Ireland, written in 1187, quaintly describes this remark- 

 able reputed process as follows : 



"Chap, n, Of Barnacles which grew from fir timber 

 and their nature. 



" There are likewise here [in Ireland] many birds called 



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