In the past several years the analysis of ancient DNA has become widely use
d in paleontology and archeology. DNA has been reported to have been isolat
ed from a variety of organisms up to a hundred million years old. The analy
sis of these DNA molecules has been used to draw conclusions about phylogen
etic relationships, migration of populations, and the emergence of pathogen
s. It has become apparent, however, that many experimental artifacts are as
sociated with the study of ancient DNA and in several cases the DNA purport
ed to have been of ancient origin has been shown to be due to contamination
. This review will summarize the sources of ancient DNA, the information co
ntained within it, the methods of analysis, and the limitations of these te
chniques.