144 SECRETS OF EARTH AND SEA 



with the stock from which they originally diverged a 

 repugnance which may be overcome by human contrivance 

 or by natural accident, but is, nevertheless, an effective 

 and real quality. Distinct forms, which have not arrived 

 at the stability and separation characteristic of species, are 

 spoken of as " races," or " varieties." It is very generally 

 the case that the " races " of one species can inter-breed 

 freely with one another, and with the original stock, when 

 it still exists. Comparatively little is known as to the be- 

 haviour of wild or naturally-produced " races." Practically 

 all our views on the subject of " races " and their inter- 

 breeding are derived from our observation of the immense 

 number and range of " races " and " breeds " produced by 

 man as farmer, fancier, and horticulturist. It has been 

 generally received as a rule, that the various races pro- 

 duced in the farm or garden by breeding from a species, 

 will inter-breed freely, and produce offspring which are 

 fertile. A special and important series of races, in which 

 human purpose and voluntary selection necessarily have 

 a leading part, are the races of man. 



The offspring of parents of two different races is called 

 a mongrel, whilst the term " hybrid " has been of late 

 limited, for the sake of convenience, to the offspring of 

 parents of two different species. Mongrels, it has been 

 generally held, are fertile often more fertile than pure- 

 bred individuals whose parents are both of the same race, 

 whilst " hybrids " are contrasted with them, in being in- 

 fertile. We have seen that infertility is not an absolute 

 rule in the case of hybrids, and it appears that there is also 

 a source of error in the observations which lead to the 

 notion that "mongrels" are always fertile. The fact is 

 that observations on this matter have nearly always been 

 made with domesticated animals and plants which are, of 

 course, selected and bred by man on account of their 

 fertility, and thus are exceptionally characterized by 



