Stargate SG-1 (1997–2007)
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Unnatural Selection 

Having regained control of the X-303, the SG-1 team finds itself in an unknown part of space. Rescue comes in the form of the Asgard, specifically Thor, who needs their help. The Asgard ... See full summary »



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Episode cast overview:
G. Patrick Currie ...
Fifth (as Patrick Currie)
Kristina Copeland ...
Fourth (as Rebecca Robbins)
Sgt. Siler
Thor (voice)
Sara O'Neill (archive footage)


Having regained control of the X-303, the SG-1 team finds itself in an unknown part of space. Rescue comes in the form of the Asgard, specifically Thor, who needs their help. The Asgard home world has been overrun by the Replicators and they require SG-1's help as well as the relatively low tech X-303. The Asgard had set a trap for the Replicators and hoped to use a time dilation device that would give them the time they need to find a way to defeat them. The problem is that the Replicators have turned off the device and the Asgard want SG-1 to go in and activate it. They accept the assignment but to meet their objective, O'Neill will face a moral dilemma. Written by garykmcd

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Release Date:

10 January 2003 (USA)  »

Company Credits

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Technical Specs


Sound Mix:

| (Dolby 5.1)


Aspect Ratio:

16 : 9
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Did You Know?


That incredibly tough material, neutronium, is repeatedly mentioned. Neutronium is made when the electron shells of atoms are collapsed and all matter becomes one giant nucleus of neutrons. A piece of neutronium the size of a double cheeseburger would weigh about as much as all of New York..the state, not the city. Unfortunately, neutronium could only exist under enormous pressure, literally tens of millions of pounds per square inch. See more »


Just after Carter reveals that there was nothing left on the planet but the miles-deep stack of Replicator blocks and the building in front of them, they go down stairs that are full of spider webs. See more »


Jonas Quinn: You instructed every replicator out there to come to you?
Colonel Jack O'Neill: I have a theory why you lost the war.
See more »


Features Stargate SG-1: Cold Lazarus (1997) See more »


End Title
Written by Joel Goldsmith
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User Reviews

So Far The Best Episode
21 May 2017 | by See all my reviews

The X-303 is located in an unknown part of the universe and Sam does not know how to route to return to Earth. Out of the blue, Thor appears at the bridge and tells that the Asgardian are monitoring Earth and it was possible to follow the X-303. He asks for help to O'Neill and the SG-1, since Asgard has been overrun by the Replicators. They used the android Reese to summon all the Replicators in the universe to trap them in a time dilatation device. However their plan failed and now they want to use the SG-1 and the X-303 to activate a time device to return to the original plan. O'Neill succeed to get authorization to proceed the mission and on the arrival, they learn that the Replicators have reverted the dilatation device and six of them have evolved to the human form. Now they want to explore the SG-1 minds to learn their knowledge and life experience. What will happen to the SG-1?

"Unnatural Selection" is so far the best episode of "Stargate SG-1" with a great story. The plot is highly attractive and O'Neill's unethical and Machiavellian decision in the end is logical despite the moral dilemma of Carter and the group. Fans will certainly be disappointed since Five's humanity could be a hope to save the universe from the Replicators. His surprise with Sam's attitude and this action may bring consequences to the SG-1 in the future episodes is the great question. My vote is ten.

Title (Brazil): "Unnatural Selection"

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