When people see young, attractive women in relationships with older and/or unattractive men, the usual perception that comes to mind is that the relationship revolves around money. This perception is usual because it tends to be accurate: women do, in fact, tend to prefer men who both have access to financial resources and who are willing to share them. What is rather notable is that the reverse isn't quite as a common: a young, attractive man shacking up with an older, rich woman just doesn't call too many examples to mind. Women seem to have a much more pronounced preference for men with wealth than men have for women. While examples of such preferences playing themselves out in real life exist anecdotally, it's always good to try and showcase their existence empirically.
This leads to a new paper by Arnocky et al (2016) that examined how altruism affects mating success in humans (as this is still psychology research, "humans" translates roughly as "undergraduate psychology majors", but such is the nature of convenience samples). The researchers first sought (a) to document that more altruistic people really were preferred as mating partners (spoilers: they are), and then (b) to try and explain why we might expect them to be. Let's begin with what they found, as that much is fairly straightforward. In their first study, Arnocky et al (2016) recruited 192 women and 105 men from a Canadian university and asked them to complete a few self-report measures: an altruism scale (used to measure general dispositions towards providing aid to others when reciprocation is unlikely), a mating success scale (measuring perceptions of how desirable one tends to be towards the opposite sex), their numbers of lifetime sexual partners, as well as the number of those that were short-term, the number of times over the last month they had sex with their current partner (if they had one, which about 40% did), and a measure of their personality more generally.
These measures were then entered into a regression (controlling for personality). When it came to predicting perceived mating success, reported altruism was a significant predictor (ß = 0.25), but neither sex nor the altruism-sex interaction was. This suggests that both men and women tend become more attractive to the opposite sex if they behave more altruistically (or, conversely, that people who are more selfish are less desirable, which sounds quite plausible). However, what it means for one to be successful in the mating domain varies by sex: for men, having more sexual partners usually implies a greater level of success, whereas the same does not hold true for women as often (as gametes are easy to obtain for women, but investment is difficult). In accordance with this point, it was also found that altruism predicted the number of lifetime sexual partners overall (ß = .16), but this effect was specific to men: more altruistic men had more sexual partners (and more casual ones), whereas more altruistic women did not. Finally, within the contexts of existing relationships, altruism also (sort of) predicted the number of times someone had sex with their partner in the last month (ß = .27); while there was not a significant interaction with sex, a visual inspection of the provided graphs suggest that if this effect existed, it was being predominately carried by altruistic women having more sex within a relationship; not the men.
Now that's all well and good, but the authors wanted to go a little further. In their second study, rather than just asking participants about how altruistic they were, they offered participants the opportunity to be altruistic: after completing the survey, participants could indicate how much (if any) of their earnings they wanted to donate to a charity of their choice. That way, you get what might be a less-biased measure of one's actual altruism (rather than their own perception of it). Another 335 women and 189 men were recruited for this second phase and, broadly, the results follow the same general pattern, but there were some notable differences. In terms of mating success, actual altruistic donations (categorized as either making a donation or not, rather than the amount donated) were not a good predictor (ß = -.07). In terms of number of lifetime dating and sexual partners, however, the donation-by-sex interaction was significant, indicating that more charitable men - but not women - had a greater number of relationships and sexual partners (perhaps suggesting that charitable men tend to have more, but shorter, relationships, which isn't necessarily a good thing for the women involved). Donations also failed to predict the amount of sex participants had been having in their relationship in the last month.
With these results in mind, there are two main points I wanted to draw attention to. The first of these concerns the measures of altruism in general: effectively charitable behaviors to strangers. While such a behavior might be a more "pure" form of altruistic tendencies as compared with, say, helping a friend move or giving money to your child, it does pose some complications for the present topic. Specifically, when looking for a desirable mate, people might not want someone who is just generally altruistic. After all, it doesn't always do me much good if my committed partner is spending time and investing resources in other people. I would probably prefer that resources be preferentially directed at me and those I care about, rather than strangers, and I might especially dislike it if altruism directed towards strangers came at my expense (as the same resources can't be invested in me and someone else most of the time). While it is possible that such investments in strangers could return to me later in the form of them reciprocating such aid to my partner, it seems unlikely that deficit would be entirely and consistently made up, let alone surpassed.
To make the point concrete, if someone was equally altruistic towards all people, there would be little point in forming as kind of special relationship with that kind person (friendships or otherwise) because you'd get the same benefits from them regardless of how much you invested in them (even if that amount was nothing).
This brings me to the second point I wanted to discuss: the matter of why people like the company of altruists. There are two explanations that come to mind. The first explanation is simple: people like access to resources, and altruists tend to provide them. This explanation should hardly require much in the way of testing given its truth is plainly obvious. The second explanation is more complex, and it's one the authors favor: altruism honestly signals some positive, yet difficult-to-observe quality about the altruist. For instance, if I were to donate blood, or my time to clean up a park, this would tell you something about my underlying genetic qualities, as an individual in worse condition couldn't shoulder the costs of altruism effectively. In this sense, altruism functions in a comparable manner to a peacock's tail feathers; it's a biologically-honest signal because it's costly.
While it does have some plausibility, this signaling explanation runs into some complications. First, as the authors note, women donated more than men did (70% to 57%), despite donating predicting sexual behavior better for men. If women were donating to signal some positive qualities in the mating domain, it's not at all clear it was working. Further, patterns of charitable donations in the US show a U-shaped distribution, whereby those with access to the most and the fewest financial resources tend to donate more than those in the middle. This seems like a pattern the signaling explanation should not predict if altruism is meaningfully and consistently tied to important, but difficult-to-observe biological characteristics. Finally, while the argument could be made that altruism directed towards friends, sexual partners, and kin are not necessarily indicative of someone's willingness to donate to strangers (i.e., how altruistic they are dispositionally might not predict how nepotistic they are), well, that's kind of a problem for the altruism-as-signaling model. If donations towards strangers are fairly unpredictive of altruism towards closer relations, then they don't really tell you what you want to know. Specifically, if you want to know how good of a friend or dating partner someone would be for you, a better cue is how much altruism they direct towards their friends and romantic partners; not how much they direct to strangers.
Last, we can consider the matter of why people behave altruistically, with respect to the mating domain. (Very) broadly speaking, there are two primary challenges people need to overcome: attracting a mate and retaining them. Matters get tricky here, as altruism can be used for both of these tasks. As such, a man who is generally altruistic towards lot of people might be using altruism as a means of attracting the attention of prospective mates without necessarily intending to keep them around. Indeed, the previous point about how altruistic men report having more relationships and sexual partners could be interpreted in just such a light. There are other explanations, of course, such as the prospect that generally selfish people simply don't have many relationships at all, but these need to be separated out. In either case, in terms of how much altruism we provide to others, I suspect that the amount provided to strangers and charitable organizations only makes up a small fraction; we give much more towards friends, family, and lovers regularly. If that's the case, measuring someone's willingness to donate in those fairly uncommon contexts might not capture their desirability as partner as well as we would like.
References: Arnocky, S., Piche, T., Albert, G., Ouellette, D., & Barclay, P. (2016). Altruism predicts mating success in humans. British Journal of Psychology, DOI:10.1111/bjop.12208