224 ESSENTIALS OF BIOLOGY 



As a first approximation we may say that such local races 

 represent natural, irreducible, morphological categories of animals 

 living in the wild. The progeny of the animals belonging to a 

 local race are recognizable as also belonging to that local race. 

 But we shall see that even these local races are also logical 

 categories of organs. 



78. ON HEREDITARY RESEMBLANCES 

 We proceed now to qualify the above statement of what we 

 mean by '' heredity." It would not be true to say that the parents 

 are *' similar " to the progeny. By " similarity " we mean that 

 two things are so much alike that they cannot be distinguished from 

 each other, no matter how^ carefully we investigate them. This 

 is never the case with regard to parents and offspring : (i) 

 Because parent and offspring are always animals in different phases 

 of a life-history and are, therefore, not similar ; (2) there is 

 generally sexual dimorphism : the offspring, whatever its sex, 

 is always sexually different from one parent and this difference 

 includes not only the essential sex-organs, ovaries and testes 

 but it may also include external genital organs and un-essential 

 bodily characters (such as hair on the face in men) that go along 

 with sex. (3) There may ht polymorphic castes : thus the progeny 

 of a queen bee includes females, males and neuters, castes which 

 are well-distinguishable morphologically. So also with ants, etc. 

 Of course, in parthenogenetically and vegetatively reproduced 

 races such sexual polymorphism does not exist. (4) Finally, there 

 are always what we shall C2\\ fluctuations of morphological character 

 in the individuals of a local race and even in the individuals of 

 the same "' brood " or progeny. It does not matter here that 

 these fluctuating differences are " non-inheritable," they are still 

 differences. 



Therefore the characters of the parents are not similar to the 

 characters of the progeny, but this does not spoil our statement 

 of what is meant by heredity, (i) Because the definition of the 

 characters by means of which we define a local race, say, is a 

 definition of those characters at all phases in the life-history so 

 that, although the young animal may be very different from the 

 adult, these differences are included in the definition of the 

 category. (2) The definition includes both male and female 



