Ahhhh (hollywood) Zombies! My favorite topic since I was a kid. My first was "Return of the living dead" in 1990 and despite the cheesiness of this movie, I have been passionate by the topic ever since. Up to this day, I have seen almost every possible movie involving undead creatures and read a ton of fiction related to the subject. At 34 now, I do still collect fictions, roleplay book, board games, video games about zombies... (Please don't judge me. ;) anyway I assume this 100%)
For me this passion took place in the fact that it was a gruesome but oh so efficient horror model. Imagine yourself being chased by a rotting and mindless corpse of a human trying to eat you alive! It scared the living hell out of me and as a therapy, I decide to confront it and learn from it. Back in the days me and my best childhood friend spend hours discusing the famous question: "What would you do during a zombie outbreak?" And folks do not lie, you ALL have a contingency plan. It is a fun ice breaker in a stalled conversation, try it, you will learn a lot about your interlocutors!
Anyhow, we declined this theme on so many level that it was ridiculous and strangely because of that, I learned so much on many subject like survival, social skills, medical skills, weapons, food storage... The possibilities are endless!
OK before I loose you guys, I will get to what I think is an interesting analogy with some of the corpus researched here.
Zombies are "mentally dead" and those mindless creatures have only one purpose (in unlife :)) to feed on the livings. The absurdity is that they do not even need it to exist, but hunting the living is their only function. In that regard, they are 100% mechanical, stupid and incapable of adaptation but they are relentless and use their great number to overpower their victims. A victim that will turn zombie with only a bite.
The living are the opposite. They are smart, faster and at times stronger. They could team up and collaborate for surviving purposes. However, due to the dangerous nature of this world, they have to be extremely careful. Some could lose their humanity along the line as they strip themselves of their emotions as emotions are a liability when one is forced to brutal and cruel surviving options. Madness is not far away when you are surrounded by death and danger.
But if the zombies are a menace, it is always the human factor that end up being the most detrimental and we could see that in almost ALL the zombies movies, and who is the most dangerous type of enemies. A psychopath in a position of power.
Now replace zombies by OP, living by souled human and put psychopaths wreaking havoc and corrupting the whole atmosphere... Well... Are we not living in a zombie World already? ;)
I guess people don't need to look like the average zombie to act like one. Massive chaos, shortage of supplies, group think and the approaching wave intensifying the already intense emotions of such an event could turn people into raving, murderous lunatics IMO (that is, if a plague didn't already wipe most of us out). And that's not including the wild DNA changes that Laura has shown are very well possible. Well that's the good news! 
