Evolutionary displays of group aggression refers to reasons why groups go against outsider groups;
You can use lynch mobs as its what I used for psya3 in january but you have to describe lynch mob behaviour from an evolutionary perspective.
Genocide is a form of institutional aggression and is not part of evolutionary explanations of group displays of aggression.
For lynch mobs in brief I wrote about;
How lynch mobs killed thousands of black people in the late 19th century, linked this to the power-threat hypothesis, then dehumanisation and how these two were evolutionary; killing rival groups increases your own groups survival chances through greater access to resources, more women, better chance for reproducing etc.
Dehumanisation was evolutionary as it made the process of killing easier in itself which would normally be hard to do; but dehumanising rival group members in ritualistic killings (lynchings) made it easier to kill rival group members to increase their own adaptive fitness (hence evolutionary).
then throw in supporting studies and evaluation.
The biggest one is that evolutionary explanations tend to be post-hoc and after the event has happened, they are difficult to prove or disprove and can argue both ways.
Such group behaviour could be argued to go against evolutionary behaviour as mixing with outsider groups would increase genetic diversity and create stronger genes hence why it can be argued both ways yet this states we go against outsiders...etc etc.
I posted my own model essay answer many months ago; search my posts with attachments and you should find it; that will tell you everything you need to know.
good luck!