Rational ideas. Rick's group are the ZA balance, only going off in a "fringe" direction when absolutely necessary (Rick biting Joe's neck, the initial, pacifistic plan to release Randall, despite the danger he posed if he reunited with his allies, etc.).
Maybe that--barring overwhelming circumstances--is what gives them the edge: other groups only operate in extremes of violence, threats or barbarity. As seen with Tomas, Randall's bar friends or Woodbury--barbarity only opened the floodgates of self destruction.
I kind of see it that way too now. Clearly the ultimate way to live is to be open to living every way, as conditions require. We are now into yet another group who think they have the best way to live figured out & are sticking to it. That is a disadvantage, assuming one way to live is all you need to do, the way Woodbury did, or the way they thought at the prison. People who think they got it figured out are destined to be ruined eventually
That's what Rick's final words meant. What all their experiences add up to makes them rather profoundly tenacious, and that is this. Of all the groups or gangs we've seen in 4 seasons, the trait that none of them have more so than Rick's current band, is adaptability.
Evolution is just continuing to adapt to accept preferred or necessary advantages
All true. But I would add: it's more than just being adaptable. It appears the Terminus folks have made adaptations that have worked quite nicely, and it's going to backfire on them anyway. And really, I'd say Michonne did a good job of adapting before she met Andrea, but she also lost herself in the process.
I'd repeat that Rick's group is unique because they hold to a higher standard (or at least remain moderate) while still being willing to adapt. Like
TREK_GOD_1 said, they're capable of going off in a "fringe" direction when necessary, but only then.
What it adds up to is that Rick's group wasn't adaptable until they learned it the hard way. They've had a lot of costly lessons, but they did learn. It could be argued that Joe's group was extremely adaptable as well ... but they learned nothing.
The "learning" aspect and the "peace vs. war" aspect I mentioned earlier could almost be broken down into seasons.
In Season 1 they were just plain learning about their situation.
In Season 2 they tried to practice peace on the farm. They learned some hard lessons from that. Fortunately, they managed to survive the lessons.
In Season 3 they practiced, if not war, then significant hostility. We had the return of the Ricktatorship, the kick-ass raid to clean out the prison, Rick's suspicion of Tyrese's group which led to kicking them out, raiding Woodbury, and almost turning over Michonne. Michonne trying to practice her survival-hostility and seeing what was likely to happen if she kept it up. Daryl trying to go back to his old ways with his brother and discovering that he couldn't. Eventually they (or at least Rick, Michonne, and Daryl) learned the futility of much of that. Again, fortunately they managed to survive the lessons.
Finally, Season 4 was about integrating both war and peace, and practicing both moderation and adaptability. That's where they are now. In the future surviving their lessons won't happen just because they're fortunate, but because, as you say, they've evolved.