No matter how hard men try, they may not be able to hide their aggression. A study in male ice-hockey players suggests that to gauge a man's aggression levels, you just have to look at the proportions of his face.
Cheryl McCormick and Justin Carre from Brock University in Ontario, Canada, found that the larger the width-to-height ratio of a player’s face, the more aggressive they were.
They measured aggression by the number of penalty points each player accrued for potentially harmful behaviour, such as elbowing and fighting.
In general, men's faces tend to have a larger width-to-height ratio than women's. This physical characteristic has been linked to higher levels of testosterone, which in turn is linked to aggressive behaviour.
Interesting quote from the Physiognomonica attributed to Aristotle:
εν εκαστω γενει θηλυ αρρενος μικροκεφαλωτερον εστι και στενοπροσωποτερον και λεπτοτραχυλοτερον
in each genus, the female has a smaller head than the male, and a narrower face and a thinner neck
and the Physiognomonica attributed to Polemon:
τον ευφυην τοιουτον ειναι νοει ... επηρμενα προσωπα και σαρκωδη, ου μην λεπταand the Physiognomonica of Adamantius:
consider the man of good nature to be such... raised and fleshy faces, but not narrow
το θηλυ ως επι το πολυ εχει του αρρενος ... προσωπον στενωτερον
the female in most cases, compared to the male, has ... a narrower face
A reader asks in the comments whether men are indeed broader-faced than women. Looking at the data of Farkas et al. [International Anthropometric Study of
Facial Morphology in Various Ethnic Groups/Races], it appears that this is not the case. Out of the 25 groups where both male and female data exist, in 19 men have a higher facial index (narrower-faced) than women, and in 6 the opposite is true.
Here are the 6 groups where men have broader faces than women (greater difference first):
Slovaks [men's F.I. = 97.6% women's], Czechs, Germans, Hungarians, Vietnamese, Angolan [men's F.I. = 99.9% women's]
The median ratio of men/female F.I. is 101.9% (Slovenians); for Greeks it is 102%, very close to the median. For white Americans, the ratio is 102.3%.
I also looked at Howells' craniometric data, which includes a wider sampling of world populations, taking the ratio of Nasion-Prosthion/Bizygomatic. The ratio of the male to the female average is 99.5%, practically the same.
So, while men do have wider faces in the absolute sense (mean +7.6%, median +3.6% in the Howells set; mean +5.6%, median +6.3% in the Farkas set), they do not appear to have wider faces in terms of proportions compared to women.
[I will comment further when I read the article]
UPDATE (Aug 21)
I have posted the abstract below. They looked at the upper face, not the total face height, thus the data of Farkas et al. (which did not measure upper face height) are not relevant. But, the skull data of Howells is relevant, and do show the predicted sexual dimorphism, although not very noticeable on a global scale.
The authors cite Weston et al. (2007).
Young children possess shorter, broader faces relative to those of adults. However, a distinction between the sexes can also be observed that is linked to distinct male and female growth trajectories (Figure 1). Analysis of individual traits against age indicates that male and female growth trajectories diverge at puberty for BZW but not for FHT (Figures S2 and S3). This relationship of width-to-height of the upper face deviates from predictions based on ontogenetic scaling, as males (which are, on average, larger than females) have similar facial heights to females, whereas facial breadth is larger in the maleThey used a South African collection to arrive at this conclusion.
I examined ZYB/NPH on either Europeans or Zulu, and list the mean and median values of the trait for men and women:
So, these don't look supportive of greater ZYB/NPH in males than in females. In this paper, the authors measured ZYB/NPH from photographs. It is very difficult to get an accurate estimate of the nasion, prosthion or zygomata using a photograph; the authors report high inter-rater reliability, but reliability means that different raters measure similarly, not that they measure correctly!
In particular they measured upper facial height from the brow to the lip. Their photograph indicates that they took this measurement from the lower point of the eyebrows. Since men are both hairier and don't remove eyebrow hair, it is quite possible that women's upper facial height was inflated. In any case, taking the upper facial height from the brow is not consistent with taking the nasion-prosthion height.
So, while the conclusion that broader-faced men are more aggressive is correct, the explanation that it is due to men having a higher breadth/upper face ratio seems suspect.
Proceedings of the Royal Society B doi: 10.1098/rspb.2008.0873
In your face: facial metrics predict aggressive behaviour in the laboratory and in varsity and professional hockey players
Justin M. Carré, Cheryl M. McCormick
Facial characteristics are an important basis for judgements about gender, emotion, personality, motivational states and behavioural dispositions. Based on a recent finding of a sexual dimorphism in facial metrics that is independent of body size, we conducted three studies to examine the extent to which individual differences in the facial width-to-height ratio were associated with trait dominance (using a questionnaire) and aggression during a behavioural task and in a naturalistic setting (varsity and professional ice hockey). In study 1, men had a larger facial width-to-height ratio, higher scores of trait dominance, and were more reactively aggressive compared with women. Individual differences in the facial width-to-height ratio predicted reactive aggression in men, but not in women (predicted 15% of variance). In studies 2 (male varsity hockey players) and 3 (male professional hockey players), individual differences in the facial width-to-height ratio were positively related to aggressive behaviour as measured by the number of penalty minutes per game obtained over a season (predicted 29 and 9% of the variance, respectively). Together, these findings suggest that the sexually dimorphic facial width-to-height ratio may be an ‘honest signal’ of propensity for aggressive behaviour.