I'm a man in my 30s, and I'm looking to settle down and start a family. I was falling in love with the woman I've been seeing for six months, who seems lovely, intelligent, and kind. Recently, I arrived at her place early and overheard her arguing with her mother on the phone. She was yelling, swearing, and being very nasty. I'm close to my parents and can't conceive of speaking to them this way. She never mentions her parents, beyond saying she isn't close with her mother. She's only been sweet and doting to me, and she seems well-liked by her friends and co-workers. Could she have hidden anger issues?

--Shocked

"Till death do us part" tends to come earlier than expected if your wife's idea of marital compromise is either you say, "Yes, Dear" or she garrotes you with the wire on a cat toy.

It's understandable you're worried there's a rage-filled, profanity-spewing ladymonster just under the sweet girlfriend veneer. However, because someone expresses anger in an ugly way at another person doesn't necessarily mean: 1. They are out of control; or 2. They will express themselves this way with everyone. (To be fair, it can mean one or both of these things.)

Anger often gets a bum rap, demonized as a "toxic," "negative" emotion. Aristotle knew better, suggesting only fools never get angry (though he didn't get into the subject of screaming a string of profanities at Mom). Our emotions, including so-called negative emotions like anger, are our protectors: motivating us to act in ways that make us more likely to survive, mate, and pass on our genes. For example, anger surges in us when we perceive that another person is treating us unfairly: shorting us on what we feel entitled to -- whether money, love, respect, or our fair share of cake.

Anger seems to function as a bargaining tool to incentivize better treatment, explains evolutionary psychologist Aaron Sell and his colleagues. "Acts or signals of anger" communicate that unless the other person mends their unfair ways, we might "inflict costs" (maybe go all screaming maniac on them) or "withdraw benefits" (possibly exile them from our circle of friends). This suggests it might be in their interest to "recalibrate" their behavior in our favor: stop being so disrespectful, stingy, and/or cake-hoggy.

Anger as a selective "hey, don't do me like that!" tool is different from anger as a way of being: "high trait anger," a chronically angry disposition. People with this disposition have "a short fuse," flying into a rage at the slightest provocation, explains evolutionary social psychology researcher Julie Fitness. They see the world and others in narrow terms -- "right" or "wrong" -- and are grievance hunters, ever on the lookout for "apparent injustice." They are quick to lash out and blame others when things don't go perfectly, and in relationships, they create a "climate of fear and loathing, with anger or the threat of it serving to intimidate and control" their partner.

If your girlfriend were this sort of person, wouldn't you know? One could argue she might be a scary-explody person who's managed to hide her true nature. That seems unlikely, given how the chronically angry tend to see a sick plot against them if the diner gives them three less raisins on their oatmeal than the guy at the next table.

You're shocked -- partly because you wouldn't talk to your parents this way. Consider the possibility that your girlfriend has a different sort of parent: unloving and toxic. And consider a reason people jack up the volume and ugliness: They repeatedly perceive they aren't being heard. (This is especially painful if you're speaking to your parent and they have a history of being physically present but emotionally vacant.)

If your girlfriend feels like an unloved daughter (or some shade of that), she might be ashamed of it and see it as something to hide. She might suspect there was something wrong with her, unlovable about her (rather than understanding her mother as broken: unwilling or unable to be loving in the way every kid needs from their mother).

To encourage your girlfriend to open up to you, ask about her mom in a way that suggests she should redirect any shame she might be feeling. Tell her you feel bad her mom seems to be a continuing source of pain for her and that she deserved -- and deserves -- better. Getting her to talk about her relationship with her mother -- plus observing, over a few months, how she reacts in tough situations -- should help you figure out whether there are any big red flags. As the saying goes: "Love is never having to scream, 'I will end you! And then bury you in 36 pieces in a shallow grave!'"

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.