THE PRESENT POSITION OF THE THEORY OF ORGANIC EVOLUTION . 95 



origin of the dog, he arrives at the conclusion that all the 

 domesticated breeds are derived from several wild species, which 

 fall into two main categories, viz., those allied to Cants lupus, the 

 northern wolf, and those allied to the jackal, Canis aureus. No 

 doubt the blood of these species has been crossed again and again. 

 But, as visitors to the Zoological Gardens can convince them- 

 selves, there is nothing in the anatomy of either wolf or jackal 

 which could possibly account for the peculiarities of the Chinese 

 pug, of the dachshund, and of the greyhound. 



If then the wide divergence between domesticated breeds is 

 not to be accounted for by their origin from distinct species or 

 by the crossing of different species, to what then is it to be 

 ascribed? Darwin, after a long acquaintance with practical 

 breeders, answers the question thus : — by the mating together 

 of carefully selected specimens which show in the most marked 

 degree the "points" which the breeder desires to emphasize. 

 Darwin says that to select the proper individuals, a lifetime of 

 experience is needed, since the points in which the selected show 

 their superiority over their neighbours are often only visible to 

 the trained eye. 



Since all the " points " or characters of animals differ in 

 intensity of development from individual to individual, and since 

 either over-development or under-development seems to be 

 inheritable, by careful selection practised through a number of 

 years almost any amount of deviation from the original type 

 can be achieved, 



Darwin next points out that in every species of animal far 

 more young are produced than can possibly survive ; indeed, it is 

 obvious on reflection that where the animal population of a 

 district remains the same from decade to decade, on an average 

 only two of the offspring born of a single pair of parents survive 

 to enjoy adult life and to raise offspring themselves. But let 

 any lover of birds reason out the number of nestlings raised by 

 a pair of sparrows, for instance, during their lifetime, and then 

 calculate what a destruction of nestlings must ensue. Under 

 such circumstances, as Darwin points out, the surviving two will 

 be those best fitted to their surroundings— that is those which are 

 best adapted to gain food, withstand cold, and evade their enemies. 

 Under normal circumstances this elimination of all but the most 

 fit, generation after generation, will keep the average of health 

 and strength in the species at a high level, but if the circum- 

 stances change, if the climate becomes colder, wetter or warmer, 

 or if a new class of enemies turns up, then the standard of what 

 is fit will change also, and by the survival of a slightly different 



