This episode is part 2 of 2; it is preceded by "Prometheus".

"Unnatural Selection" in the twelfth episode of the sixth season of Stargate SG-1.


After retaking the Prometheus, Thor asks SG-1 for their help in defeating the Replicators once and for all, since the Replicators have taken over Hala and have taken Human form. The only way to ensure the success of taking them down is to trust Fifth, one of the Replicators.

Previously on Stargate SG-1[]

SG-1 discovers the android Reese, the creator of the first generation of Replicators and send her to the Asgard for study. The Prometheus is stolen by rogue NID agents and taken into hyperspace. SG-1 manages to retake the ship but are stranded. Thor arrives and requests their assistance as the Replicators have invaded their homeworld.


Thor, who has rescued SG-1, informs them that he needs their help to defeat the Replicators and because the Prometheus isn't very advanced (compared to Asgard standards), they could fly unchallenged into Replicator-controlled territory. In addition, he informs them that the Asgard were able to call all Replicators back to one point, their first colony world, Hala, by using a signal found in the android Reese. They then tried trapping them using a time dilation device, in a sphere encompassing the entire planet, but their plan ultimately failed. If they are allowed to escape, they will conquer the Asgard and most likely be drawn to the Milky Way and Earth's raw materials. Now he wants SG-1 to solve this problem but Colonel Jack O'Neill is by no means interested in this operation. Thor brings them back to Earth, where he beams up supplies from Stargate Command and transports extraneous passengers off the Prometheus, except SG-1, to the planet.

Jack later uses a holographic communicator to contact Major General George S. Hammond and briefs him about the situation. Afterward, he talks with Major Samantha Carter about the Asgard plan and then goes to the cargo bay to eat something, where he meets Jonas Quinn and Teal'c. They talk about the Replicator threat then feel themselves losing speed. Thor tells them that they have reached their target but the time-dilation device has long since been changed so that time now passes faster within the field ("by a factor of ten squared," as Thor explains). Thor wishes them luck and departs.

Unnatural Selection 1

The unnamed Replicator controlled Asgard ship

Unnatural Selection 2

The Prometheus landing on Hala

SG-1 flies near Hala, is scanned by a Replicator-controlled vessel, and enters the atmosphere of the planet. They land on a large surface with only one construction, the one spot on the planet that breaks the smooth terrain. As SG-1 steps outside, it turns out that the whole ground consists of Replicator blocks. They enter the nearby building and find the time-dilation device, when suddenly a man appears. Then, four more human-like persons appear and an older man demands that Carter stop her work on the device. The groups reveal that they are in fact replicators. Upon hearing this, SG-1 opens fire on them—–with no success. Suddenly, several bug-like replicators appear and surround the team, so they are forced to disarm. The leader of the five human-form replicators offers O'Neill his hand but when O'Neill takes it, the man seemingly pushes his hand into O'Neill's head and Jack finds himself in the Gate room where the man appears. The replicator tells him that they are in O'Neill's unconscious mind. Eerily, the replicator starts to read O'Neill's mind, including his Iris Deactivation Code. The two go through an imaginary Stargate. The replicator leader tells O'Neill they will go on a journey "to every place you've ever been."

SG-1 wakes up, finding themselves back on the Prometheus. It turns out they have all experienced the same thing, one of the replicators entered their minds. They determine they were out for 37 hours. In order to decimate this new threat, they plan to blow up the hyperspace engines. Jonas suggests they try reasoning with the replicators instead, but O'Neill just wants to blow them up.

However, when they go to execute this plan, they meet one of the human-form replicators, who calls himself Fifth. He carried each of the humans back to the ship, so they would be more comfortable. Fifth tells them that they are invited for meal with the other human-form replicators. He also says exploding the ship would only feed energy to the replicators. Fifth leaves, and Carter suggests they try to find out as much as they can about the evolved replicators and try to report back to Thor.

SG-1 returns to the building and First tells them about their history and construction. First explains that, instead of the larger replicator blocks, they consist of microscopic cell units. They modeled themselves on the form of their creator, Reese. There are currently six of the human form replicators.

First also tells them that it was he who deactivated the time-dilation device and reprogrammed it. They converse about Reese and the error that embedded in her systems. He says their purpose is still to increase their number. First, with a condescending attitude about him, reveals that they attempted to correct the error that Reese had in Fifth, yet First says Fifth is weak. First says they intend to explore SG 1's minds over and over until they have learned everything they can. Fifth is ordered to enter one of the human minds and Carter agrees to do it. However, instead Fifth brings Carter into his own unconscious mind so that he can communicate secretly with her. Carter says Fifth is more like humans than replicators. He says the other replicators will destroy him if he tries to help them. She says if he will help her repair the time dilation device, the replicators will be frozen in time and Fifth can come with them.

SG-1 awakens again with Fifth telling them that he has reconfigured the device. While Jonas and Teal'c return to the ship, Carter programs the device. However, she is secretly ordered by O'Neill to set the time on three minutes instead of the predetermined five, which they originally told Fifth to be the setting. SG-1 starts toward the ship after telling Fifth to head there himself shortly after three minutes. First suddenly appears and tells Fifth that SG-1 has lied to him but Fifth is adamant in his convictions about SG-1's honorability. He looks at the timer and is shocked to find that it's nearly to zero. Just as it activates, SG-1 leaves the planet. However, both Jonas and Carter feel bad that they used Fifth's "humanity against him." O'Neill insists that Fifth was not human and tells the team they did the right thing.

Back on Hala, Fifth and the other Human-Form Replicators stand there, trapped in the device.


Appearances for Unnatural Selection





Sentient Species




Notable quotes[]

Thor: The contents of your armory at Stargate Command, along with appropriate attire, food and other supplies you may require, are now being transported aboard this vessel.
O'Neill: I hope you did the paperwork.

O'Neill: Suffice to say, you might want to get upstairs and punch one on the old speed dial.
Hammond: My grandchildren?
O'Neill: Two, then.

O'Neill: They didn't go for it.
Carter: They didn't approve the mission?
O'Neill: No, they did that. Once they knew the stakes and the whole "fate of the universe" stuff. Both the President and Hammond realized we had no choice. He sends good luck, God speed, and all those things he says when he thinks we're going to die.
Carter: So what didn't they go for?
O'Neill: The name I suggested.
Carter: For the ship?
O'Neill: Yeah.
Carter: Yeah. Sir, we can't call it the Enterprise.
O'Neill: Why not?
Carter: The code name for the project is Prometheus. What's wrong with that?
O'Neill: It's a Greek tragedy. Who wants that?
Carter: Okay. The X-303 it is then.

Thor: If you wish to reconsider...
O'Neill: No, no. I full-well expected the other shoe to drop eventually.
Thor: We can only hope that this will be the last footwear to fall.

O'Neill: What is with you people? Time machines are nothing but trouble. Even we know that!

First: Your mind is incredible.
O'Neill: Well...
First: Such chaos, and humor, and pain.


Main Characters

Guest Stars


  • "Unnatural Selection" was originally titled "X-303, Part 2," according to Cult Times magazine.
  • Thor described Hala as the "first planet settled by the Asgard."
  • O'Neill initially wanted to call the Prometheus Enterprise, a reference to Star Trek. He also objected to the name Prometheus, due to the tragic origins of the name.
  • When O'Neill and Jonas Quinn are called away while O'Neill drills Jonas on reloading the FN P90 Personal Defense Weapon, Jonas places the weapon back in the crate loaded. Most likely due it being a 'crash course' in offensive weapon training.


  • Calculating the time it would take to leave the 0.16 light year radius of the time dilation field at the top speed of 110,000 miles per second (as Major Samantha Carter stated), it would take them approximately 100 days flat out to get to a safe distance from the planet and not be affected by the time dilation field. (100 days field time, 2767 years Earth time (factor 10^4))
  • When eating ice cream, at one point Teal'c trades his chocolate for O'Neill's semi-white of some kind (possibly Cherry Garcia?). As they're called to the bridge, O'Neill sets down a vanilla one and Teal'c sets down a chocolate one.
  • After Thor mentions that the Replicators have activated the time dilation field with a factor of 10 squared (or 100), Carter remarks that within one hour 4 days have passed inside the fields, which is roughly correct. Immediately afterwards she says that depending on when they did this hundreds of years could have passed for the replicators. However Thor mentioned earlier that even with the X-303 in tow the journey to the Asgard galaxy only took several hours (and the trip from the Asgard galaxy presumably being faster), thus in a worst case the time dilation field could only have been active for 6 hours (any longer and Thor would likely have noticed before heading towards the Milky Way), depending on the exact interpretation of "several hours", which in turn would translate into only 24 days, which is far from "hundreds of years".
  • Fifth states that "There are four minds to explore at least once", however SG-1 consists of five minds. The symbiote that Teal'c carries also has a mind that the Replicators could have explored, and given that the Goa'uld are the dominant race in the Milky Way galaxy, the symbiote's memories should have been of particular interest to the Replicators.


  • Nominated Leo for "Dramatic Series: Best Director" (Andy Mikita)

Other languages[]

  • French: Évolution (Evolution)
  • Italian: IL Tempo Immobile (The Still Time)
  • Spanish: Selección Antinatural (Unnatural Selection)
  • Czech: Nepřirozený Výběr (Unnatural Selection)
  • Hungarian: Természetellenes kiválasztódás (Unnatural Selection)
  • German: Unnatürliche Auslese (Unnatural Selection)
  • Russian: Неестественный отбор (Unnatural Selection)

Links and navigation[]

Smallwikipedialogo This page uses content from Wikipedia. The original article was at Unnatural Selection (Stargate SG-1). The list of authors can be seen in the page history. As with SGCommand, the text of Wikipedia is available under the GNU Free Documentation License.
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