So the Evolved all are because of parasites which I'm sure you all know. And because of the parasites the Evolved are able to evolve to be different from normal, and still look a bit normal. I'm sure you all can tell that so far from what I have presented to you they all have different intelligence levels with Flames and Freezers being the smartest and Jars and Basics being the dumbest. With the different intelligence levels there is also different aggression levels. Like how you'll notice that Stalkers and Megabeasts are the most aggressive. If you want them to be more tame and 'human like' then you just have to remove and kill the parasite. This will lessen their symptoms therefore saving some types from death or permanent damage to their bodies. This will also make them most commonly very docile with occasional outbursts of rage and aggression.