PROBLKM 4. The Effect of the Enviroimient on the Orgainsm 



487 



1200 — 



1050 - 



9-10 10-11 11-12 12-13 13-14 14-15 15-16 16-17 17-ls 



Fig. 436 Tl:>e results of measuring large mimbers of beans are given in the table. 

 These results were used in making the graph at the left. Note the few extrejnely 

 s?nall and extremely large beans, the many medium-sized bea?is. Variations of this 

 kind arranged in a graph give a bell-shaped curve. 



exactly alike, for you know that individ- 

 uals differ, first, in their genetic make-up 

 and secondly, in their environment. 

 Many years ago someone recorded the 

 chest measurements and heights of the 

 soldiers in a Scottish regiment. He 

 found a wide range from the short men 

 to the very tall men, from those with a 

 narrow chest to those with a broad chest. 

 Whenever a single character is measured 

 and the measurements are carefully listed 

 we discover an interesting fact. If enough 

 individuals are measured there is usually 

 a very si^radual change from those at one 

 end of the scale to those at the other. 

 This shows up best when one makes a 

 diagram of the table of fisrures. Such a 

 diagram is called a graph. After study- 

 ing the graph in Figure 436, you will 

 find it interesting to make graphs as de- 

 scribed in Exercises 4 and 5. 



What Lamarck thought about varia- 

 tions. About the year 1800 Jean Baptiste 

 L.amarck (1744- 1829), a French biolo- 



gist, called attention to the fact that the 

 environment causes changes in organisms. 

 The person constantly exposed to strong 

 sunlight acquires a darker skin. He saw, 

 too, that frequently as an animal used 

 some part or organ, the part or organ 

 grew larger or stronger; when allowed 

 to fall into disuse, it became smaller 

 or weaker. We all have seen examples 

 of this many times. The muscles of a 

 bookkeeper are usually smaller than those 

 of a steel worker. Lamarck was con- 

 vinced, as you are today, that the envi- 

 ronment causes changes in animals and 

 plants. 



But then Lamarck went one step 

 further. He said that a variation of this 

 kind would be passed on to the offspring, 

 even if only to a slight degree. He be- 

 lieved that if an ors^an had been much 

 used by the parents it would be slightly 

 better developed in the offspring; and 

 that if the organ had grown less efficient 

 because of disuse, it would be slightly 



