The film American Beauty featured a plastic bag poetically swirling on an eddy of air and went on to win five Academy Awards. Even so, I still can't think of those bags as beautiful. But just as a pathologist can admire the structure of a particularly virulent and contagious virus, I must admit that I feel a strange attraction to them.

According to a 1997 study, 58 percent of Americans prefer paper bags to plastic ones; yet a 1996 report by the Film and Bag Federation found that four out of five grocery bags we actually use are plastic. How to explain the discrepancy? Supermarkets have made it difficult to choose anything but plastic.

Stores have a financial interest in keeping their checkout lines moving smoothly, and having more than one option at the end of the line slows things down. A spokesman for Ralph's, one of California's large supermarket chains, would not admit to any company bias other than 'customer choice,' but a checker I spoke with at one of their stores told me that employees were explicitly instructed to use plastic if the customer expressed no preference. As you might expect, the issue is cost. Plastic bags cost about four cents each, while the average paper bag costs twice that amount. Paper bags hold between two and three times as much as plastic ones, but when all the numbers are crunched, supermarkets still save by pushing plastic -- especially when you factor in all those 'single-bag' orders in which a customer's entire purchase fits into a single sack.

Nothing epitomizes the mindless profligacy of our consumer culture like these cheap, flimsy, yet depressingly indestructible little bags that get caught up in our trees, litter our streets, and wash up on our beaches. Americans throw away 100 billion polyethylene bags a year. The bags choke thousands of marine animals annually; the inks used to print all those smiley faces break down in landfills and create a toxic seep. Though plastic bags take up less than 4 percent of all landfill space, estimates on how long they take to decompose range from 100 to 1,000 years.