Geoff > it's just not correct to state that humans never got cancer in hunter-gatherer days

Actually that claim was first made by Stanislaw Tanchou in 1843 in his regular lecture at The University of Paris Medical School.   He found that the most accurate way to predict epidemiological cancer rates was by examining per-capital grain consumption rates.  These proved to have a striking correlation in all areas where these data were gathered.  He thus predicted that no cancer would be found in people who didn't eat grain.  Until the prevalence of Acrylamides in human blood samples was discovered in 2001, scientists had no idea why correlation was so.
 
Many explorers and missionaries, inspired by Tanchou, began to search for cancer among hunter-gathers.  In the resulting 100 year search for cancer in such people, documented by Anthropologist Vilhjalmur Stefansson, none was ever found except among those of those eating missionary food.
 
Steve Jobs died at almost the exact average lifespan ( 56.8 years) of middle-class vegetarians ( who have access to modern medicine) in India.  Incidences of Pancreatic cancer is growing at the fastest rates of all cancers found in the US.  It is usually associated with aflatoxin ingestion.  It is pandemic in Africa, Mexico and other places whee people eat large amounts of irrigated corn.
 
Montezuma's revenge - it's not just diarrhea anymore!
 
Ray Audette
 
Stefansson, Vilhjalmur, 
Cancer: Disease of Civilization. 
New York: Hill and Wang, 1960.