14 THE STORY OF ANIMAL LIFE 



one becomes a navvy and one a clerk. In five 

 years' time these two young men will probably 

 be very different in appearance from one another. 

 The navvy will have developed his muscles; he 

 will be broad-built, broad-chested, and strong. 

 The clerk, on the other hand, will probably be 

 comparatively weak and slim, his chest will not 

 be so broad, his muscles will not be so well de- 

 veloped. The navvy, too, will probably be of a 

 fresh complexion, while the clerk will be pale. 

 All these differences are due to the fact that their 

 bodies have adapted themselves to circumstances. 

 Both men may be equally healthy, and equally 

 long-lived. Let us take another example. Let 

 us compare two other youths, of whom one be- 

 comes a cobbler and one an Alpine guide. The 

 latter, in five years' time will have become a per- 

 fect specimen of muscular humanity active, agile, 

 and hardy. The cobbler will be comparatively 

 stiff in his limbs and unable to undertake any 

 singular feat of muscular exertion, although he 

 may be able to do a very hard day's work at his 

 own trade. The mountaineer, too, will probably 

 differ in disposition from the cobbler. He will 

 be daring, resourceful, and not afraid of danger 

 under circumstances which would terrify the cob- 

 bler. Now let us suppose that the sons and grand- 

 sons of the navvy are brought up to be navvies, 

 and the sons and grandsons of the clerk are 

 brought up to be clerks; that the children and 

 grandchildren of the Alpine guide follow his own 

 calling, and the children and grandchildren of 

 the cobbler do the same ; we shall probably 

 have four families differing very much in type 

 of physique from one another. Yet take one of 

 the navvy's sturdy grandchildren and bring him 



