THE STUDY OF INHERITANCE. 489 



be better able than the mediocres to crush through the thick 

 grass and foliage whenever he was scampering for his life, to 

 jump over obstacles, and possibly to run somewhat faster than 

 they. So far as he is small of his kind, he would be better able 

 to run through narrow openings, to make quick turns, and to 

 hide himself. Under the general circumstances it would be 

 found that animals of some particular stature had on the whole a 

 better chance of escape than any other ; and if their race is close- 

 ly adapted to these circumstances in respect to stature, the most 

 favored stature would be identical with the mean of the race. 

 Though the impediments to flight are less unfavorable to this 

 (stature) than to any other, they will differ in different experi- 

 ences. The course of an animal might chance to pass through 

 denser foliage than usual, or the obstacles in his way may be 

 higher. In that case an animal whose stature exceeded the mean 

 would have an advantage over mediocrities. Conversely the cir- 

 cumstances might be more favorable to a small animal. Each 

 particular line of escape might be most favorable to some par- 

 ticular stature, and, whatever this might be, it might in some 

 cases be more favored than any other. But the accidents of foli- 

 age and soil in a country are characteristic and persistent, and 

 may fairly be considered as approximating to a typical kind. 

 Therefore those which most favor the animals of the mean stat- 

 ure will be more frequently met with than those which favor 

 any other stature, and the frequency of the latter occurrence will 

 diminish rapidly as the stature departs from the mean. 



" It might well be that natural selection would favor the indefi- 

 nite increase of numerous separate faculties if their improvement 

 could be effected without detriment to the rest : then mediocrity 

 in that faculty would not be the safest condition. Thus an in- 

 crease of fleetness would be a clear gain to an animal liable to be 

 hunted by beasts of prey, if no other useful faculty was thereby 

 diminished. 



" But a too free use of this ' if ' would show a jaunty disregard 

 of a real difficulty. Organisms are so knit together that change 

 in one direction involves change in many others; these may not 

 attract attention, but they are none the less existent. Organisms 

 are like ships of war, constructed for a particular purpose in 

 warfare as cruisers, line-of-battle-ships, etc., on the principle of 

 obtaining the utmost efficiency for their special purpose. The 

 result is a compromise between a variety of conflicting deside- 

 rata, such as cost, speed, accommodation, stability, weight of guns, 

 thickness of armor, quick steering power, and so on. It is hardly 

 possible in a ship of any established type to make an improve- 

 ment in any one of these respects without a sacrifice in other 

 directions. If the fleetness is increased, the engines must be 



