That Thinking Feeling

Psychology's answers to everyday questions, in blog form!

Should I steal my friend's boyfriend?


Today’s blog is written by my brilliant friend, Dr Kate Cross, who has just had a shiny new paper about mate choices published here. She is a Lecturer in Comparative and Evolutionary Psychology at the University of St Andrews, and she specialises in sex differences in human behaviour. You can follow her on Twitter @CatharineCross.

Dr Kate Cross

Dr Kate Cross


Should I steal my friend’s boyfriend? Excellent question. The short answer is: tread carefully if you wish to remain friends with your friends. For a longer answer, let’s do some psychology.

Choosing the same sex partner as your friends makes perfect sense if you’re, say, a female grouse [i]. She gets nothing but sperm from her grouse spouse, so she should choose a partner based on whether he has good quality genes. Copying other grice’s spice is a short-cut to doing this effectively. We humans, on the other hand, are (often) hoping to get more than sperm from a male partner – like long-term companionship and support – so why would you choose someone who’s already taken?

A grouse in the wild

A grouse in the wild


Mildred’s ideal partner is small, brown and currently dating Linda.


The answer, according to some evolutionary psychologists, is: human males are tricky to evaluate as partners. For many women who are sexually interested in men, the ideal male partner is someone who looks hot, but is also pleasant to be around, interested in commitment, and willing to help raise children. Looking hot is fairly easy to evaluate, but these other qualities are harder. So why not let other women do some of this work for you? A man who has already made a commitment to another woman is clearly interested in commitment, right? And this other woman has judged him to be worth getting involved with. So, why not go for that one?

There are a number of studies out there which appear to show support for this idea [ii]. Many of them go a little bit like this: (straight) women look at pictures of men’s faces and rate their attractiveness. They rate the same faces as more attractive if they have information that suggests other women are interested.

Case closed, right? No. First we need to answer at least three questions:

  1. Do ratings of attractiveness translate into real-life romantic interest?

  2. Is it even a good idea to pinch someone else’s partner?

  3. What’s special about men’s faces?

Let’s start with 1. Do ratings of attractiveness translate into real-life romantic interest?

Rating the attractiveness of a picture of someone’s face is one thing: Deciding whether or not to ask them out is another. (Present me with 100 gorgeous people looking for a date and I’ll agree that they’re all gorgeous, but at least 95 of them will have to go home.)

One way of answering this question is to ask partnered men if they agree with statements like: In general, I feel that I have become more attractive to other women since I started dating my girlfriend. Vakirtzis and Roberts [iii] did this with men in heterosexual relationships, and those men did indeed agree. But maybe men who have girlfriends feel more self-confident than men without girlfriends. Maybe this increased self-confidence causes other women to be more interested in them – or just causes them to think women are more interested in them. Or maybe men are not 100% accurate when judging women’s sexual interest [iv]. That’s before we take into account the fact that men in relationships might actually be in those relationships because they are more attractive – which is bad news for testing any kind of link between relationship status and attractiveness [v].

If you have a mind like mine, you are currently thinking, An experiment! An experiment is the thing to do. Let’s take some men and present them as ‘single’ or ‘taken’, and see what women think then. Good idea. 

Close-up on two people shaking hands

Close-up on two people shaking hands


“Hello, I’m Brian, and I’m married.”


OK, then – 2. Is it even a good idea?

That depends. What are your local cultural norms about monogamy? (Ask around if you’re not sure.) If they are pro-monogamy, are you willing to break them? Are you sure this is your best option? Is he literally the last man alive?

Assuming you go for it, you might be thinking: But wait: if he’s willing to leave her for me, then won’t he leave me for someone else? And the answer would appear to be: Maybe. It seems that relationships that begin with one partner being ‘poached’ are not particularly satisfying or stable [vii].

Now for 3. What’s special about men’s faces?

The studies I mentioned at the beginning showed that (straight) women think men’s faces are more attractive if other women like them. There are two possible conclusions:

a)       The reason for this is something specifically to do with choosing a mate – straight women have an evolved tendency to be attracted to others’ partners because it helped their straight-woman ancestors choose good ones (see above).

b)      People just copy the preferences of others when we’re unsure about something – anything. People have evolved this tendency because it helped stop our ancestors making all kinds of errors – like eating poisonous berries (which no-one else was eating), building our huts on a flood plain (where no-one else was building), poking dangerous animals with sticks (etc etc etc). It’s just that if you test straight women on their preferences for men’s faces, it will look like they have a specific tendency to copy those.

I favour b), and I will tell you why. 

Uller and Johansson [vi] recruited 97 female participants and put them in a room with a man who was either wearing, or not wearing, a wedding ring. The participants were instructed to get to know the man, using a pre-set list of questions including: Where do you live? and What do you do for a living? After this interaction, the participants were asked questions like: How willing would you be to have sex with him? They did not answer this question more positively when he was wearing the wedding ring. This suggests that the situation certainly isn’t as simple as ‘married men are more attractive than unmarried men, and that’s easily detected’.

A man and a woman laughing among foliage and flowers

A man and a woman laughing among foliage and flowers


Sure, he’s got a nice face, but what does he think about these berries I’ve just found?


Some of my colleagues and I [viii] presented women with pictures of men’s faces. We gave them real information about the preferences of other women doing the experiment at the same time. We found the same effect for faces as in previous studies – being told that other women find a face attractive does boost our attractiveness ratings for that face. But… exactly the same thing happened when we showed them pictures of abstract art. Furthermore, we got exactly the same results when we included bi and lesbian women in our analysis – groups who are usually excluded in these kinds of studies. It doesn’t seem to matter if you actually view men as potential partners or not – the pattern of copying is the same. This suggests it’s not a specific mate-choosing mechanism at work.

I think what we’ve shown is that women copy the preferences of other women when they’re unsure about how to make a choice. If what you test people on is their ratings of men’s faces, then it might look like we have some special mechanism for copying mate preferences. But if all we had ever tested them on was abstract art, we might have come to a completely different conclusion.

So the answer to the question: Should I steal my friend’s boyfriend? is: Probably no, but consider nicking that Alma Thomas painting they have.