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.