How could the current H1N1 "swine flu" variation develop naturally?

Influenza viruses can infect multiple species of animal.

This is really not hard. Birds migrate, they take the flu with them. Humans travel they take the flu with them.

An Asian bird migrates to Europe taking a bird flu with them. That flu finds it's way into a human who gets "bird flu" and infects others. One of the poor unfortunate souls who picks up this "bird flu" is a sick elderly person who already has a form of human flu.

The two flu's combine and infect healthcare workers, then the healthcare workers kids, then the healthcare workers kids classmates, then the healthcare workers kids classmates parents. One of those parents gets infected, travels to Mexico on vacation, and passes this "combined flu" to one of the workers in the hotel. That worker passes it to their families.

One member of their family is already infected with a form of swine flu. That family member is now infected with a combination swine-bird-human flu.

This is not all that uncommon. What is uncommon is for these combined flu's to spread so late in the flu season. Which theoretically ends in mid-Spring.

The Centers for Disease Control and Prevention(CDC), and World Health Organization(WHO), agree that it was caused by a pig who got both swine, and avian flu. It gave it to a human, and while infected, the human got Human flu. This caused the flus to "merge", and created H1N1 A flu.

in case you look on the information with reference to the variety of "deadly" flu circumstances shown with H1N1 virus, even on the CDC's very own internet site, you will discover the media hype and warnings did not upload as much as an "epidemic." in short, rip-off.