Born from fear. "Survival of the Fittest" is really about hate. And fear. Grounders, Ark-people, Mount Weather people, it's all about their survival, so fear from dying becomes hate, and hate makes them take stupid decisions.
Grounders and Ark people keep walking a tightrope, everything on the line. Fear of losing power, hate about past slights, makes one or two situations go further than they should. Darkness keeps permeating everything around them, and so, the feeling of dread is high. In that respect, this episode is another good one.
But the show is not playing it safe, so it decides to expand on two more story lines. Lincoln and Bellamy's plan to enter Mount Weather is fraught with danger. Will they be able to get inside? How can they get through without being discovered? Is this the start of a beautiful friendship? This one(two)man-mission by Bellamy is nicely done, and it teases us which much more to come if he gets inside the complex.
Talking about beautiful friendships... Jaha keeps his path to become a prophet, and harbors an interesting obsession about bringing his people to the magnificent City of Light. On this religious trip he decides Murphy would be a nice partner. Jaha is showing all the signs of one who believes he has a call, talking about god and being a leader, etc etc. This new strand is also an interesting one, which may further the world of "The 100" and stress the religious aspect, which till now has been kept on a tight leash. Religion and sci-fi make for interesting partners, so lets see if they explore it further.
For now, all this plot development makes for an interesting second season episode.