Invasion on ABC

Surface on NBC

Threshold on CBS

There's something different about this season's new TV shows: the emphasis on fear. Each major network introduced a new series about sinister alien invasions: "Invasion" on ABC, "Surface" on NBC and "Threshold" on CBS (which is in jeopardy of extinction after moving to a new night).

They follow Steven Spielberg's version of the very first space alien invasion story, H.G. Wells' "The War of the Worlds" last summer. It was a blockbuster hit.

So what's under the surface of these invasions? What are we on the threshold of? The 1950s?

That's when the template for alien invasion drama was set, amidst the suppressed hysteria of the early atomic age and the Cold War. Although disguised in genre sensationalism, their correspondences to the sources of paranoia were pretty much one to one. Soviet bombers and missiles might come without warning to destroy from the sky; so do space aliens. But communists also subvert from within, fellow Americans could be fellow travelers and your neighbor might be a spy. So "Invasion of the Body Snatchers" led a subgenre of aliens taking over the minds and bodies of humans.

So who are the 21st century aliens? Who, or what, are we so afraid of now?

The terrorist is the obvious alien. "There can be no doubt that, even subconsciously, 9/11 is a thematic undercurrent in our show, for sure," said Threshold producer Brannon Braga.

But the obvious may not be the whole story. These shows imply other possibilities. With ancient and Biblical antecedents, the fear of nature and natural forces perverted by human actions has been a science fiction theme from "Frankenstein" to "Soylent Green" and "The Day After Tomorrow." In the 1950s, it was expressed as the monster created by nuclear radiation mutations (giant ants, locusts, spiders, etc.) or awakened by atomic explosions (Godzilla.) All three of these shows suggests variations appropriate to our contemporary Zeitgeist.

"Invasion" began with an alien-induced hurricane in its first episode, aired while the Katrina catastrophe was unfolding. "Surface" reveals alien life forms living in the sea. Our easily resurrected fear of ferocious animals may combine with stubbornly repressed suspicions of climate change distortions, undoubtedly enlivened by this year's record-breaking hurricane season.

When we feel alienated from our own planet, we fear some well-deserved Revenge of the Earth. Even Spielberg's alien machines emerged from the ground instead of falling from the sky as in the original Wells.

In "Threshold," the invasion is also a subversion. Its unseen aliens rearrange the DNA of human victims by means of a "signal" manifested as sound. Genetics is our generation's Dr. Frankenstein science, and the mating of the biological and the electronic -- viruses and computer viruses -- demonstrates another aspect of our paranoia: it is often about what we don't quite understand.

These aliens apparently attempt to transform us into versions of them, proposing a kind of Close Encounter of the Fourth Kind: We have met the alien, and he is us. We probably suspect that endangered species, for instance, might very well see us that way.

William S. Kowinski writes frequently for Insight from Arcata. Contact us at insight@sfchronicle.com.

Story continues at sfgate.com.