FLIGHTLESS BIRDS AND THEIR FATE. 83 



the results of the modification of the same organ 

 in different animals for the same purpose. Or 

 to put it in another way, it shows us how the 

 need to overcome certain mechanical obstacles 

 demands that every organism or part of an 

 organism shall adopt one common plan of a 

 nature demanded by the particular obstacle to 

 be overcome. The superficial appearance in all, 

 is as a result, the same, however different may 

 be the underlying structures. 



Let us take, first of all, one or two illustrations 

 of the adaptation of animals originally very dif- 

 ferent one from another but now very similar. 



Once upon a time, ages and ages ago, certain 

 reptiles or lizard-like animals found life more 

 tolerable and food easier to procure near the 

 sea-shore, and occasionally in the sea itself 

 Of these some were more expert in catching 

 food in the water than others. Some slight 

 difference in their power of keeping out the 

 water from the lungs, a broader hand, greater 

 power of remaining for a long time sub- 

 merged, and so on, gave them an advantage 

 over their fellows which their offspring shared, 

 and not only shared, but possessed in greater 

 perfection. Exactly in so far as they became 

 more successful in these -respects, so in exactly 

 the same proportion did they become more 

 unlike their unsuccessful friends, and more 

 unlike their own parents and grandparents. 

 Eventually, after many generations, all obvious 

 relationship was lost. This process of trans- 

 formation was aided and hastened, by a weeding 

 out, which worked by the gradual killing off of 



