You see this figure a lot when you start reading about cancer: About 78% of all malignant disease is diagnosed in people 55 years or older. (American Cancer Society. Cancer Facts & Figures 2010) For that reason alone one would expect to find fewer cases in earlier centuries, a point I made in my recent Times story. By examining skeletons from the days of the Neanderthals through the year zero (when B.C. became A.D.) anthropologists have calculated that the mean lifespan was 30 years with a maximum of about 45. I read that in an interesting new book, How It Ends: From You to the Universe by Chris Impey, a professor of astronomy at the University of Arizona. (The book is not only about human longevity but also the longevity of the universe, a dizzying sweep across subjects. So far I’m up to page 50.)
The same low life expectancy continued through the Renaissance, Dr. Impe writes, except for royalty who could expect to live until 50. (Reading that brought to mind the autopsy of the mummy of Ferrante I of Aragon, the 15th century King of Naples, who died at 63 apparently from metastatic colon cancer.) It has been only in the last two centuries that lifespan has been increasing. By 1900 the rest of us (at least in the developed world) had caught up with Renaissance kings and queens: Children born in 1900 could expect to die at 50. For those born in 2000 life expectancy is 80.
All that was mostly familiar but Dr. Impey surprised me with this observation: almost all of the gain in lifespan came from a reduction in childhood mortality. “In other words it’s a myth,” he wrote, “that our ancestors endured lives that English philosopher Thomas Hobbes had labeled ‘nasty, brutish, and short.’”
Now I’m not sure what to think. If an abundance of infant deaths, through accident or infanticide, dragged down the average life span, then a significant number of people who survived childbirth might have lived well past 50. If so that would cast some doubt on the assertion that old age is the predominant reason there is more cancer today. What we need to know is the median, not the mean. More things I need to sort out.
I have been grappling all week with the issue of longevity as I try to finish a draft of my third chapter, which concentrates on ancient cancer. Archaeologists of the future exhuming a 21st century graveyard will surely find more cancer than in, say, a medieval crypt. But some scholars like Luigi L. Capasso, an Italian anthropologist, have argued that the discrepancy cannot be explained entirely by our living longer. He points to “the very strange fact that an increase in cancer prevalence has also been noted in countries in which life expectancy was minimal in the past century.” (Capasso, L. L. (2005), Antiquity of Cancer. International Journal of Cancer, 113: 2–13). I just read in the CIA World Fact Book that life expectancy at birth ranges from 38.48 (so precise!) in Angola to 89.78 in Monaco.
But isn’t there an easy rebuttal to Dr. Capasso’s argument? These countries would also be the ones with poorer nutrition, higher rates of chronic infection, and rising tobacco use. More people in the third world, mostly children, die from diarrhea than people die from cancer in the developed world. (That is also from the Impe book.) In poor countries now undergoing rapid development there will be increased urbanization, with more chances of spreading human papilloma virus and hepatitis, which are associated with cervical and liver cancers. If medical care in these countries is improving (from abysmal to mediocre) more cancer might be detected and better records kept. Some of the rise would be an illusion. As the country grows more prosperous people will be slowly adopting the lifestyles of the industrialized world, gaining weight (obesity is strongly linked with cancer incidence) and longer lifespans.
Dr. Capasso’s implication is that there is more cancer today because of industrial carcinogens. So many friends I talk to take that for granted. Until recently I would have too. But the deeper I dig, the less evidence there seems to be. It is all so much more complicated.