Which male traits are being sexually selected for?

Those of us interested in human evolution spend a lot of time looking into the past, so it can be easy to forget that evolution is an on-going process that continues to shape our species. One of the most often discussed forces shaping our current evolutionary trajectory is sexual selection. Simply speaking, this is the fact that certain attributes are viewed as attractive by the opposite sex – often because they indicate that the possessor would be a good mate – thus having that trait means you will be more successful at reproducing. The trait spreads throughout the population and before too long everyone has it; often to an exaggerated degree.

I find sexual selection fascinating because it means that our deeply personal opinions of what is attractive aren’t actually our own, but have been shaped by millions of years of natural selection driving us to pick the best mate. Loads of research has been published on the topic, so clearly I’m not the only one interested by the topic.

Most of this work consists of identifying a trait that a lot of people find attractive in the opposite sex, then suggesting it is sexually selected for. Some of these attractive attributes include chest and facial hair on men (perhaps because it signals the owner is mature and thus would have had time to acquire resources to invest in offspring) and a certain hip to waist ratio in women (possibly because it shows they would be good at giving birth).

Whilst having a beard was attractive, too much beard had the opposite effect. "Heavy stubble" was deemed nicer than "full beard"

Whilst having a beard was attractive, too much beard had the opposite effect. “Heavy stubble” was deemed nicer than “full beard”. Similarly, a waist to hip ratio in women that was too high or too low was deemed unattractive

The problem with this sort of research is that for evolution to occur the trait has to increase your chance of reproducing not just make people think you’re attractive. Granted being attractive probably helps, but we don’t know if the effect is significant enough to be an evolutionary driving force. Fortunately new research is being conducted to help fill in this gap in our knowledge and figure our whether what we find attractive is influencing our evolution.

An international team of researchers recorded a large group of men and asked women to rate how attractive they were. They then analysed the photographs in an effort to see what traits made a man seem attractive. The results weren’t too surprising, with things such as being tall, having a certain facial structure and so forth meaning you would be perceived as more attractive. These are the classic traits many people believe to be under the influence of sexual selection.

They then went back to these men and found out how sexually successful they were, and whether this was connected to how attractive they had been rated.  The results may surprise you, because they showed that attractiveness didn’t have a strong influence on mating success. The women indicated that being a bit brawny but with a slightly feminine face and a voice that wasn’t too deep was the most attractive, but possessing those traits didn’t mean that a man would be sexually successful. The exception to this was height. Being tall was the only attractive trait that also increased the chances a man would get lucky.

So what about men made them likely to be successful with the ladies? The researchers got a group of men to also look at these individuals and rate them in terms of how dominant they looked. Interestingly, they found that being perceived as more dominant was much better at predicting whether or not the man would be sexually successful. Dominant traits included a very deep voice, overly masculine face and other traits which were the exact opposite of what women found most attractive.

Whilst being dominant may help with the ladies, I don’t think this will

Evolutionary speaking, this would mean it was competition between men rather than appealing to women which was the primary driving force behind the development of many masculine traits, such as a deep voice. Further, this continues to be a powerful force in the present day, with more dominant men getting more ladies than even the most attractive guy; as counter-intuitive as this may seem.

However, this study is far from perfect. For example, they don’t bother looking at personality. It may be that the most attractive people are as fun to be around as a donkey’s anus, hence why they don’t have as much success as one might think. Further, this was a fairly limited study, only examining 63 men or so from one part of the world (and asking a mere 72 women what they found attractive). It may be that this handful of women had an unusual taste.

So, whilst more research is needed these results clearly have fascinating implications. They suggest that the development of “manly” traits was actually the result of men trying to out-compete other men and ultimately being good as such competition is what will get a guy the ladies. Conversely, being an attractive man doesn’t translate to mating success, suggesting sexual selection may not be as an important force in our evolution as once thought.

References

Dixson AF, Halliwell G, East R, Wignarajah P, & Anderson MJ (2003). Masculine somatotype and hirsuteness as determinants of sexual attractiveness to women. Archives of sexual behavior, 32 (1), 29-39

Dixson, B. J., & Brooks, R. C. (2013). The role of facial hair in women’s perceptions of men’s attractiveness, health, masculinity and parenting abilities.Evolution and Human Behavior.

Sybil A Streeter, Donald H McBurney (2002). Waist–hip ratio and attractiveness: New evidence and a critique of “a critical test” Evolution and Human Behavior, 24 (2), 88-98

Wheatley, J. R., Dawood, K., Shriver, M. D., & Puts, D. A. (2013). Quantifying the strength and form of sexual selection on men’s traits.

Apologies for any adds you see in the article, I have no control over them. In fact, I can’t even seem to figure out what spawns them, different phrases light up as adverts each time I load the page

2 thoughts on “Which male traits are being sexually selected for?

  1. It’s likely that we evolved in scenarios with very limited potential mates where the modern practice of sitting around making visual judgements of portfolios of hypothetical partners just wasn’t providing selection pressure. Physical beauty counts as a proxy for good genes but so does dominance, physical and mental prowess, etc. Today’s culture presents a lot of visual input but we are trying to make up for a lot of the sort of information that you might have got in the past, like observing someone for a long period as you grew up together, smelling the usefulness of their immune system for your kids, knowing where they are in the pecking order, observing their hunting output, and so on.

    As I’ve said previously, it is doubtful that your genes (alone) could contain enough information to build brain systems that select partners on the basis of some of the fine-grained physical characteristic, such as the shape of the chin. A more reasonable interpretation of these preferences would be that a range of characteristics are broadly correlated: dominance, vitality, immune function, height, strength, endurance, symmetry, skin quality, mental agility, specific facial characteristics, good teeth, and so on. Detection of basic qualities like height, vitality and immune function are within the bounds of what could be reasonably expected genetically. These kind of judgements are also made by other mammals. These basic qualities would correlate with more specific visual qualities like facial characteristics and waist-to-hip ratios which would then be enhanced, tweaked and solidified by culture.

    When a college girl picks the a preferred male face in a lab, her choice is likely more culturally than genetically determined. Over time, as she selects a physical partner to actually have sex with and then to actually make babies with, the time spent together allows her to make choices that start to incorporate the drivers of choice that were active a million years ago.

    It’s also interesting to consider the impact of living in the modern world with modern nutrition supply (and health care). For virtually all of human history, food supply defined population size. This means that less successful individuals (in particular) would be getting insufficient nutrition. In this scenario, “beauty” is growing to a good size, having a bit of meat on your body, and remaining more-or-less healthy, and that, is a pretty easy pick. In the modern world we nearly all hit the standard of high beauty by paleolithic standards. (Yes, you are a supermodel! Anachronistically, unluckily or luckily.) We are still driven to select the best mates, but are forced to work with esoteric and culturally-defined metrics of mate quality.

    On the behavioral side, modern culture redirects a lot of energy from the flat-out dominance battles that occupy other great apes towards more productive pursuits. These offer something a bit like dominance but in highly abstracted cultural forms – for example, different shaped squiggles on your bank statement or your undergarments. Even dominance detection ain’t what it used to be. It’s got quite hard and confusing. For me, at least. 🙂

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