What is the term where members of a group exclude non-group members

Like the topic states, I am wondering if there is a term whereby members of a group will reject non-members of that group? The concept makes sense from an evolutionary stand-point (ie those similar to me and that I am familiar with are much safer than those who are different from me). I can't seem to find a term for it online and am wondering if it exists. I am not referring to just humans- but to all organisms, as it seems this would be a pretty standard thing across all species.
(Not sure if this is relevant but I am considering this from the stand-point that most humans, for example, have this link that helps them fit in.. and it's all hooked into what one might call the "hive mind.")