Karl J. Reinhard of Texas A&M University conducted a large study of human
coprolites from several sites in the Four Corners region of the American
Southwest. The oldest samples were from hunter-gatherers, who camped
seasonally in an Arizona cave nearly 9,000 years ago and used an area
near the front of the cave as a privy. More recent samples came from
latrines in permanent villages of Anasazi farmers that
flourished in Arizona and New Mexico of between 700 and 1,500 years ago.
   Remarkably, Reinhard could find no parasites in the hunter-gatherer
feces, but those of the farmers were laden with remains of pinworms,
tapeworms and possibly even hookworms, which can cause so much intestinal
bleeding that severe anemia may result. He estimates that the incidence
of pinworms after agriculture began at 100 percent.

  Reinhard attributes the parasite problem to the fact that sedentary
peoples live close to fecal mounds where parasites can survive, to
possible use of feces as fertilizer (a practice that continues in China
and some other places), to the high population densities that made it
more likely to transmit parasites from person to person and to
storage of grain, which attracts tapeworm-carrying rodents.

 Personal hygiene may have been no better among hunter-gatherers, but
since they were always on the move and lived in small groups, they had
less chance of picking up parasites shed by other humans. Reinhard also
notes that wild food plants are known to contain natural anti-parasite
compounds. People who depend on gathering wild foods are more likely to
consume them than are people who eat mainly corn.

From Washington Post Article

Ray Audette
Author "NeanderThin:A Caveman's Guide to Nutrition"
http://www.sofdesign.com/neander