I don't pretend to be any sort of Survivor guru , but when tribes merge it is usually one side vs another, right? Whether it be the original tribes, or some secondary flip flopped tribes. My question is do any of the tribes from premerge actually survive all the way past the merge? ie after the merge 1 of the older tribes votes out everyone on the other side systematically? Or is there always some sort of cross or double cross?

When they had Survivor Men Vs. Women... the women picked the men off one by one, but by some miraculous oversight, Chris survived and in the end won.

Then in the last one, since Steph was the only one left and she exited soon after that, that doesn't count.

There's gotta be a site that analyzes that... there just has to be.

Not sure about the rest.

This is off the top of my head, but I believe that Chris (Survivor 9?) was the only winner that came from the tribe that was in the minority after the merge. Note, this really wasn't due to any skill on his part, it was more the in-fighting between all the folks on the other tribe.

In terms of systematic elimination, I think that Thailand might have had it, although their merge came in a little late (Shii-Ann getting burned by the non-merge). After that the rest of them got picked off rather quickly. Obviously, the orginal had it but they were even at the merge and just happened to realize that they should all vote as a group to oust Gretchen. Australia would have had it if not for the fact that everyone hated Jerri and then had to boot Amber as well. All of the other ones had a few twists along the way.

Survivor Amazon never really had any chance to show tribe loyality, because not only did they come into the merge tied, but Rob C switched alliances every single episode.

I assume you mean besides season one, of course?

I'm pretty sure that's what The Robfather engineered in the All-Star season.

To lessen the chance of one tribe sysematically vote out the other one, Survivor almost always have some members from one tribe swapping with the other tribe. This gives the people a chance to get to know other tribe and potentially to get into new alliances.