According to Nina Tassler, president of CBS Entertainment, the network's decision to air two science fiction and fantasy shows next fall is not due to the success of "Lost" for rival ABC.

"We don't literally go out to the community and say, 'Because that particular show is successful on another network, please bring us that,'" Tassler said during a recent CBS' fall press preview, according to SciFi Wire.

Tassler said, "I think there's probably the appetite for such shows. But, as I've said before, every year in development, we've had some version of those kinds of shows represented."

"This year in particular, those two scripts happen to come in as strong as they did, and we had terrific pilots," she said. "So I think clearly there is something in the Zeitgeist, but for us, it was based on producing the best pilot scripts that we had."

"Threshold" follows an alien invasion and its consequences. "Ghost Whisperer" focuses on a young housewife who can interact with the spirits of the dead.

"Lost's" success is no guarantee the new shows will thrive or even survive. It all comes down to viewership. "We like to call it 'scheduling Darwinism,' survival of the fittest," Tassler said.

She is optimistic about her new shows' chances, however. "With 'Threshold,' I've been fortunate to read the first couple of scripts and see some of the early dailies. They're really embarking on a very exciting challenge."

David Goyer, co-creator for "Threshold," told fans at the recent Comic-Con International that the show had been in development a long time prior to "Lost's" airing. He did admit, though, that he felt the ABC show's success may have been one of the reasons CBS decided to pick up the series.

CBS isn't the only network adding more science fiction and fantasy to their schedule next season. Among the shows scheduled are ABC's "Invasion," NBC's "Surface," and Fox's "Night Stalker."

This fall, "Ghost Whisperer" will be seen on Friday nights at 8, followed by "Threshold" at 9 p.m. will air Fridays at 8 p.m. ET/PT.