Echo (Eliza Dushku) and her surviving Dollhouse cohorts scramble into the year 2020 to save mankind from sudden destruction. Whether they succeed, time has run out for “Dollhouse” (7 p.m., Fox) itself. This is the show’s final episode.

The failure of “Dollhouse” to find an audience is not surprising, and its underperformance can be explained by at least three major trends.

Friday nights have become dead zones for networks. Friday viewers have moved to cable, and the networks have, in turn, offered them programming that is indistinguishable from cable.

Of the four networks, only CBS still offers three original series. And all three, “Ghost Whisperer” (SyFy), “Medium” (Lifetime) and “Numb3rs” (TNT) can be seen elsewhere. NBC’s sole Friday drama, “Law & Order,” really belongs on Wednesday nights, and it will return there in March. Every other network Friday series (that is not a news magazine) is either a knockoff of a British series, a cable series or both.

The failure of “Dollhouse” also proves a point that I have made before. When a show is best known for the name of its creator, it is generally doomed. “Dollhouse” was hyped as a show from Joss Whedon, the mind behind “Buffy the Vampire Slayer” (more hyped than watched) and “Firefly” (barely watched at all). The creator-as-star promotion has repeatedly failed for Steven Bochco (“Over There”), Aaron Sorkin (“Studio 60 on the Sunset Strip”), David E. Kelley (“The Wedding Bells”) and Dick Wolf (“Deadline,” “Arrest & Trial,” “D.C.”). So there’s little surprise that it didn’t fly for Whedon.

The third and most important reason “Dollhouse” tanked was the show’s unsubtle sexism and its disregard for the large and growing female audience for sci-fi and fantasy. You don’t need to be a feminist to find the show’s premise of code geeks programming a bodacious body with a new personality every week to be a tad off-putting. Dushku was often seen bursting out of her skimpy costumes or working as an escort.

This may have worked in an earlier era. But just last year, the Sci Fi network rebranded itself as SyFy to emphasize fantasy and to attract a female audience. It has done both and it has thrived.

The feminization of fantasy certainly figured in the success of “Avatar,” now the most popular movie of all time.

In it, a gung-ho mercenary is re-educated, reformed and redeemed by his interaction with a strong (blue) woman. And the forces of corporate greed and rapacious military hardware are vanquished by Mother Nature herself.

Tonight’s other highlights

• Family secrets can be murder on “Ghost Whisperer” (7 p.m., CBS).

• A murder investigation leads to a trail of cash and drugs on “Law & Order” (7 p.m., NBC).

• Allison meets a worrisome girl from her dreams on “Medium” (8 p.m., CBS)

• Chef Ramsay mentors three bored and dispirited sisters on “Kitchen Nightmares” (8 p.m., Fox).

• An ice cream vendor sees a future in the past on “Shark Tank” (8 p.m., ABC).

• A killer targets prostitutes’ clientele on “Numb3rs” (9 p.m., CBS).

• Zoe adjusts to her new “body” on “Caprica” (9 p.m., Syfy).

• Spartacus enters training on “Spartacus: Blood and Sand” (9 p.m., Starz).