156 BIOLOGY FOR BEGINNERS 



Specialization. Robinson Crusoe on his desert island had to 

 perform all the processes needed to supply his wants. He had to 

 catch and prepare his food, make his clothes and shoes, build his 

 house and defend himself against enemies. Even though he be- 

 came somewhat skillful at all these duties he could never hope 

 to excel in any. He was, in fact, in the position of the protozoan 

 where all the life functions are performed by one cell. Even though 

 that cell be highly developed as in paramoecium or vorticella, still 

 its limit of advance is soon reached. 



Now, if there had been ten men shipwrecked with Crusoe, it 

 would have been possible for one to get food, another to prepare 

 it, others to build houses and so on. The increase in numbers per- 

 mitted division of labor. This is precisely the case with such forms 

 as volvox and all higher types; the increase in the number of their 

 cells makes possible a separation of life functions, which is actually 

 division of labor among cells. 



To return to the desert island again, if one man continued mak- 

 ing shoes or another did all the building, each would soon acquire 

 skill and perform his duty better; he would have become a special- 

 ist in his line. Cells also are able to perform their functions better 

 and better by constant use. Specialization is the term applied to 

 this condition in cells as well as in men. 



Finally, both cells and men would acquire special fitness for 

 their tasks. This special fitness is called adaptation and is 

 the permanent result of specialization. The more perfectly a 

 plant or animal is adapted to its environment, the better is 

 its chance to survive; hence this matter of development, 

 division of labor, specialization, and adaptation is of the utmost 

 importance. 



Interdependence. There is, however, another phase of this mat- 

 ter of specialization, which cannot be overlooked. The man who 

 devotes himself solely to the making of shoes, loses the ability to 

 do many other necessary things. Cells and tissues which become 

 adapted for special functions are all the more dependent upon other 

 specialized cells for equally important services. So it comes to 

 pass that the more highly specialized a plant or animal becomes 



