Typhus, Body Lice, and DDT (3 of 4)   by Dr. David L. Evans, Department of Natural Sciences Pennsylvania College of Technology    
     However, in subsequent years, earthquakes and other natural disasters
 
 
produced war-like disruptions in cities. The health authorities naturally wanted
 
 
to prevent an epidemic of typhus so they began to apply DDT. To everyone's
 
 
amazement at the time, it was absolutely useless. Fortunately, at that time,
 
 
certain antibiotics proved useful at killing the germs that actually caused typhus
 
 
but, of course, not the lice. The population of the body lice had permanently
 
 
changed because the DDT had killed all of the lice lacking the anti-DDT gene but
 
 
none of those that had the protective factor. The human body lice species had
 
 
permanently changed. This type of change brought about in the genetic make-up
 
 
of an entire species of living things is called evolution.