86 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



tat an insect has certain enemies which control its numbers and that, if we could 

 introduce those natural enemies into the area now infested by the insect, we 

 might be able to restore the balance that existed in the land of their origin. But 

 to search blindly for these natural enemies with no idea of where they are to be 

 found is a wasteful business. Sometimes that has been done, and on a few occa- 

 sions the search has, by great good fortune, been successful. On some other 

 occasions it has failed. Thus expeditions searching for natural enemies of the 

 "red scale" — an insect of much economic importance to the citrus growers of 

 California — were sent to South America, to Australia, to Africa. They secured 

 no parasites that were effective against the red scale. Why? The red scale, we 

 now are quite sure, is a native of southeastern Asia. 



How do we determine purely from sytematics where an animal came from? 

 First of all, there should be a study of the great group to which the animal 

 belongs — let us say, in this case, scale insects. By this study we arrive at an idea 

 of the minor groupings that exist. Next by a study and a mapping of the dis- 

 tribution of the species of a minor group we determine what part of the world 

 it belongs to. Then, by a more detailed study of all the species contained in this 

 minor group, we arrive at an idea of where a particular species naturally belongs. 

 Finally we can put our finger on the map of the world and say, "This is the most 

 probable place in which a search for parasites would be profitable." A study of 

 this sort indicated that parasites of the "olive scale," an insect of importance 

 in California, would most probably be found in northwestern India or Persia. 

 A search guided by this information found parasites in India, which have been 

 introduced into California and promise to be of value. 



In the field of that "environmental medicine" already discussed the syste- 

 matics of mosquitoes has demonstrated its value. Only certain species of mosqui- 

 toes carry malaria, while different species carry yellow fever and other diseases. 

 It is useless to spend money for the control of these diseases by attempting to 

 control "the mosquito." There are hundreds of kinds of mosquitoes, and the 

 recognition of the particular mosquito concerned is essential if our efforts to 

 control the disease by controlling mosquitoes are to be properly directed. 



Paleontology : There is one other field worthy of some special consideration in 

 which biological systematics has a very practical contribution to make. That is 

 the field of paleontology, which is fundamentally the recognition of the different 

 kinds of animals and plants that have lived in past times and that have left 

 fossil remains in the rocks. Paleontology could possibly be regarded as purely 

 a consideration of these fossils, but that would be relatively unprofitable and 

 it is well that it merges with, and is united with, information from other fields 

 to become historical geology. Historical geology has had not only a profound 

 influence upon the development of the idea of evolution but also upon many 

 practical matters. Time was when this was about all the explorer searching for 

 oil had to depend upon, although it is now aided and abetted by other methods, 

 but the practical aspects of historical geology still exist. 



These are merely pertinent examples, which could be multiplied many times, 

 to show that biological systematics has a proper place and at times is essential 

 to the development of a proper understanding of the world in which we live. 



In the end the systematist, if he is to fulfill his possibilities of being helpful 



