Huffington Post interviewed Seth Shostak, astronomer for the Search for Extra-Terrestrial Intelligence (SETI), prior to the airing of "Alien Encounters." He noted that there are potentially a thousand billion billion habitable planets just in the known universe. That would leave quite a bit of room for the emergence of quite a few biological life forms -- or aliens.

The episode "The Hybrid" explores the idea of combining biological systems; i.e. creating a hybrid life form out of an alien and a human. One scenario suggests that an alien presence on Earth has created "a generation of human-alien hybrids who eventually connect with a powerful quantum super computer." Shostak said the concept of one species breeding with another is still much centered in the realm of sci-fi.

"It's science fiction, of course, that they're coming here to breed with us, to make hybrids. We don't do that with other species of our own planet very often. We might crossbreed a couple species, but nobody here has got experiments to crossbreed humans with mayflies or something like that," Shostak said.

"Maybe with parrots -- that would be good because then maybe we would live longer, and we'd still be able to talk. We don't do that kind of thing because it doesn't make any sense biologically."

What Shostak means is that inter-species hook-ups are not done because there is no need for it in any biological sense. However, there are several examples of successful hybrid creations, such as ligers, tigons, and mules. However, these species are biologically compatible, unlike, say, attempting to breed a dog with a cat or chicken with a Komodo dragon. (But, then, if one takes a good look at the duck-billed platypus, there seems to have been some kind of hybridization going on somewhen back through the ages.)

But sex with aliens is most likely just the stuff of fiction. (Think: Mr. Spock of "Star Trek" fame just might be the most famous human-alien hybrid. The fictional character of Spock was the progeny of a mating between a male Vulcan and a female human.) Still, that doesn't stop the occasional UFO abduction victim from claiming to have had sex with an alien. (But abductions have been found to be more along the line of barely-conscious hallucinatory phenomena and self-created false memories than actualities.)

And even with Shostak's thousand billion billion habitable planets and the near centainty that humans are not alone in the universe, it is most doubtful that two completely foreign biological systems from different worlds could produce a working hybrid, regardless of the famous line from "Jurassic Park": "Life finds a way."

Still, sex with aliens or some type of biological experiment where humans and aliens might by hybridized would ultimately depend on the actual presence of other biological systems in the universe with which to breed. And, so far, humans seem to be alone.

And yet, there is always hope that alien life will one day be found somewhere out there in the vast reaches of space. As Shostak explained to Congress in May, extraterrestrial life will likely be discovered within the next two decades, provided that scientific research programs are properly funded.

Many point out that, mathematically, Drake's Equation proves that there has to be life in the universe. The probability is far too high that other life forms exist -- at least somewhere esle in the universe. And not only life, but intelligent life as well.

But the cautiously skeptical can always fall back on Fermi's Paradox: They may exist but where's the proof?

"Alien Encounters" airs Tuesdays on Science Channel at 10 p.m. (EST)