actually I am less sure about my statement concerning cancer in wild animals
(but my other statements remain unchanged). See

http://www.med.ohio-state.edu/physiology/faculty/Wood.html

and the following abstract [does anyone here have data on chimpanzees?]

Dig Dis Sci 1998 Jul;43(7):1443-53

Colitis and colon cancer in cotton-top tamarins (Saguinus oedipus oedipus)
living wild in their natural habitat.

Wood JD, Peck OC, Tefend KS, Rodriguez-M MA, Rodriguez-M JV, Hernandez-C JI,
Stonerook MJ, Sharma HM.

Department of Physiology, College of Medicine and Public Health, The Ohio
State University, Columbus, USA.

The cotton-top tamarin is a nonhuman primate noted for susceptibility to
juvenile onset colitis and subsequent colon cancer. About 80% develop
colitis in captive environments outside the tropics. The aim was to
determine the prevalence of colitis and colorectal cancer in tamarins living
wild in their tropical habitat. Endoscopic biopsy was used to compare
severity of colitis, inflammatory/immune cell densities, mucosal dysplasia,
and occurrence of cancer in wild tamarins in a tropical habitat with
tamarins living captive in a temperate climate. Six colon biopsies from each
of 69 captives showed severe colitis in 64.5% of biopsies and moderate
colitis in 19.5%. Severe colitis was not found in 88 wild tamarins; 13% had
moderate colitis. Densities of polymorphonuclear leukocytes, plasma cells,
and mononuclear cells in the lamina propria were related directly to the
severity of four grades of colitis (normal, mild, moderate, and severe).
Histologic or gross signs of carcinoma were detected in 12 captives and low-
or high-grade dysplasia in 15. Neither cancer nor dysplasia was found in any
of the wild tamarins. The observations suggest that colitis and cancer in
the tamarin model are linked to environmental factors.