We seem to have got away with it this time. The swine flu turned out not to be a global killer, at least not in this first go-round. But we have had a fright, and maybe we should learn something from it.

In 1994, only 10 percent of American pigs lived out their brief lives in vast factory farms. Only seven years later, in 2001, 72 percent did.

The percentage is even higher today—and it's now known that the virus that caused the outbreak in Mexico is a direct descendant of one that was first identified on an industrial-scale pig-raising facility in North Carolina in 1998.

It's not just pigs. Fewer than  300 people have died from the "bird flu" virus since it emerged in Asia in 2003. But if it became transmissible directly between human beings, it could cause a pandemic  killing tens of millions.

Did the bird flu virus also evolve on a factory farm where hundreds of thousands of chickens are crowded together? Nobody knows, but the fact that most chickens everywhere now live in battery farms certainly enhances the chance of a further mutation. And  that makes the virus transmissible human-to-human.

Industrial-scale livestock raising, a relatively recent development, is making lethal pandemics ten times more likely than they used to be.

Ten times? Okay, I'm just guessing, and you won't find scientists going out on a limb like that because they can't prove it. Scientists who go farther than the evidence will take them end up being pilloried by their colleagues: in academe, anybody who exposes a flank is attacked mercilessly by his peers, so the prudent researcher doesn't give voice to his hunches.

There has only been one major pandemic in the last  100 years, in 1918, and we won't have the hard numbers to show that pandemics have become  10 times more likely until and unless there are  10 major pandemics in the next  100 years.

But when I was interviewing experts about pandemics five years ago, just after avian flu first emerged, several of them told me off the record that that was precisely what they expected.

They wouldn't go on the record, of course, so it's left to journalists like me to say what's on their minds: the way we are getting most of our meat now is probably going to kill quite a lot of us. Just one more hazard of living in a mass society obsessed with getting maximum output at the lowest cost.

Human beings were hardly prey to quick-killer epidemic diseases at all until they started domesticating animals 9,000 or 10,000  years ago. Living in our original hunter-and-gatherer groups of  a hundred  or less, we were a poor target for diseases that killed their hosts fast, for they would quickly run out of potential hosts and die off themselves.

However, almost all the animals that human beings domesticated for food—pigs, sheep, goats, cattle, and poultry—lived in large herds or flocks. They WERE targets for epidemic diseases, because they had enough individuals to keep passing the disease on.

As the number of people in human societies grew larger—thousands, then hundreds of thousands, then tens of millions—they became potentially vulnerable to similar epidemic diseases. But even though the farmers often lived under the same roof with their animals, passing viruses back and forth, it generally took a long time before some minor mutation enabled the virus to cross the species barrier and thrive in human beings.

During the past several thousand years, major quick-killer epidemic diseases that affect human beings have emerged, on average, only once every few hundred years. But now that we keep most of our livestock in crowded cages for their entire lives, generally living above a cesspool of their own excrement and exchanging disease pathogens at blinding speed, the speed of evolution of the pathogens has accelerated dramatically.

"With massive concentrations of farm animals within which to mutate, these new swine flu viruses in North America seem to be on an evolutionary fast track, jumping and re-assorting between species at an unprecedented rate," explained Michael Greger, director of public health at the U.S. Humane Society. The same is true of bird flu viruses, and not just in North America.

The giant corporations that drove most small hog breeders out of business in the United States—from more than a million farms raising 53 million hogs in 1965 to only 65,000 facilities growing 65 million hogs today—are now active all over the world.

In Romania, for example, the number of hog farmers fell from 477,000 to just 52,00 in only four years after the agribusiness giants arrived on the scene in 2003.

The new diseases, and new strains of old diseases to which we have no immunity, will surely come, and not just one, either. We have created the ideal environment to maximize new mutations among the diseases that kill large numbers of people, and we will pay a high price. Unless we get out of factory farming, which does not seem very likely.

But then, pork prices in the United States dropped by one-fifth between 1970 and 2004, according to the U.S. Department of Agriculture. That means that factory farming is saving the average American consumer $29 a year, or about $2.40 a month. What's the risk of a lethal global pandemic compared to savings like that?

Gwynne Dyer's latest book, Climate Wars, was published recently in Canada by Random House.