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Biometric evidence that sexual selection has shaped the hominin face.

Weston EM, Friday AE, Liò P - PLoS ONE (2007)

Bottom Line: We consider sex differences in human facial morphology in the context of developmental change.A link between this developmental model and sexual dimorphism is made for the first time, and provides a new set of morphological criteria to sex human crania.This finding has important implications for the role of sexual selection in the evolution of anthropoid faces and for theories of human facial attractiveness.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University College London, London, United Kingdom. e.weston@nhm.ac.uk

ABSTRACT
We consider sex differences in human facial morphology in the context of developmental change. We show that at puberty, the height of the upper face, between the lip and the brow, develops differently in males and females, and that these differences are not explicable in terms of sex differences in body size. We find the same dimorphism in the faces of human ancestors. We propose that the relative shortening in men and lengthening in women of the anterior upper face at puberty is the mechanistic consequence of extreme maxillary rotation during ontogeny. A link between this developmental model and sexual dimorphism is made for the first time, and provides a new set of morphological criteria to sex human crania. This finding has important implications for the role of sexual selection in the evolution of anthropoid faces and for theories of human facial attractiveness.

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A comparison of male and female skeletal traits versus dental category (age class) for Pan troglodytes and Gorilla gorilla.For the chimpanzee, sexual size dimorphism is shown to be statistically significant in BZW in age classes 6 and 7 (A) and no significant sexual size dimorphism is evident in FHT for any age class (B). For the gorilla, sexual size dimorphism is evident in BZW (C) and FHT (D) for age classes 4, 5, and 7; BZW and FHT are sexually dimorphic in size as adults (age class 7). Age classes 1–7 plotted on the x axis; each class with females (F) plotted first and then males (M). Trait size on y axis (cm). The box plots indicate the median in white and the quantiles in colour. The dotted lines indicate the data range with outliers shown as isolated bars (for sample analysed see electronic Appendix in [17]).
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pone-0000710-g003: A comparison of male and female skeletal traits versus dental category (age class) for Pan troglodytes and Gorilla gorilla.For the chimpanzee, sexual size dimorphism is shown to be statistically significant in BZW in age classes 6 and 7 (A) and no significant sexual size dimorphism is evident in FHT for any age class (B). For the gorilla, sexual size dimorphism is evident in BZW (C) and FHT (D) for age classes 4, 5, and 7; BZW and FHT are sexually dimorphic in size as adults (age class 7). Age classes 1–7 plotted on the x axis; each class with females (F) plotted first and then males (M). Trait size on y axis (cm). The box plots indicate the median in white and the quantiles in colour. The dotted lines indicate the data range with outliers shown as isolated bars (for sample analysed see electronic Appendix in [17]).

Mentions: If facial variation is considered across anthropoid primates, a similar type of facial width-to-height sexual dimorphism (though more exaggerated) has been noted in the common chimpanzee and some other primates [17]. The sex variation in the chimpanzee face [17] in contrast to that of humans (Table 1,2) is mostly indicated by slope and not intercept differences, and the degree of sexual dimorphism in the traits varies. However, the same relationship between width and height of the upper face in relation to body size (ontogenetic scaling) is shown to vary between males and females in humans and chimpanzees. Figure 3 provides a comparison of male and female cranial traits (BZW and FHT respectively) versus dental age category for Pan troglodytes and Gorilla gorilla. In the chimpanzee, though size dimorphism in facial breadth is evident by dental category 6, upper facial height is not significantly different in male and female adult chimpanzees (dental category 7), in spite of the larger male body size, analogous to the condition recorded in humans. In the gorilla, both variables exhibit size dimorphism by dental category 4 and both traits are dimorphic in adults. Chimpanzee and human facial sexual dimorphism with respect to FHT are developmentally similar, and potentially explained by the same constraints of maxillary rotation and lower jaw development. This type of facial dimorphism, expressed as an index, was shown to be negatively correlated with canine height dimorphism across a taxonomically mixed sample of anthropoid primates, suggesting that there could be some kind of trade off between facial dimorphism (signalling attractiveness) and canine dimorphism (signalling aggression) [17]. If H. sapiens is included in the primate sample (see Materials and Methods, Table S2 and Figure S5), a significant inverse relationship is evident between facial and canine sexual dimorphism, with modern humans exhibiting low canine sexual dimorphism but sexually dimorphic faces. If facial structure replaced canine size, or perhaps the general possession of a large anterior dentition, as a sexual selection signal in early hominins [17], it would suggest that facial attractiveness did, indeed, play a major role in shaping human evolution.


Biometric evidence that sexual selection has shaped the hominin face.

Weston EM, Friday AE, Liò P - PLoS ONE (2007)

A comparison of male and female skeletal traits versus dental category (age class) for Pan troglodytes and Gorilla gorilla.For the chimpanzee, sexual size dimorphism is shown to be statistically significant in BZW in age classes 6 and 7 (A) and no significant sexual size dimorphism is evident in FHT for any age class (B). For the gorilla, sexual size dimorphism is evident in BZW (C) and FHT (D) for age classes 4, 5, and 7; BZW and FHT are sexually dimorphic in size as adults (age class 7). Age classes 1–7 plotted on the x axis; each class with females (F) plotted first and then males (M). Trait size on y axis (cm). The box plots indicate the median in white and the quantiles in colour. The dotted lines indicate the data range with outliers shown as isolated bars (for sample analysed see electronic Appendix in [17]).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC1937021&req=5

pone-0000710-g003: A comparison of male and female skeletal traits versus dental category (age class) for Pan troglodytes and Gorilla gorilla.For the chimpanzee, sexual size dimorphism is shown to be statistically significant in BZW in age classes 6 and 7 (A) and no significant sexual size dimorphism is evident in FHT for any age class (B). For the gorilla, sexual size dimorphism is evident in BZW (C) and FHT (D) for age classes 4, 5, and 7; BZW and FHT are sexually dimorphic in size as adults (age class 7). Age classes 1–7 plotted on the x axis; each class with females (F) plotted first and then males (M). Trait size on y axis (cm). The box plots indicate the median in white and the quantiles in colour. The dotted lines indicate the data range with outliers shown as isolated bars (for sample analysed see electronic Appendix in [17]).
Mentions: If facial variation is considered across anthropoid primates, a similar type of facial width-to-height sexual dimorphism (though more exaggerated) has been noted in the common chimpanzee and some other primates [17]. The sex variation in the chimpanzee face [17] in contrast to that of humans (Table 1,2) is mostly indicated by slope and not intercept differences, and the degree of sexual dimorphism in the traits varies. However, the same relationship between width and height of the upper face in relation to body size (ontogenetic scaling) is shown to vary between males and females in humans and chimpanzees. Figure 3 provides a comparison of male and female cranial traits (BZW and FHT respectively) versus dental age category for Pan troglodytes and Gorilla gorilla. In the chimpanzee, though size dimorphism in facial breadth is evident by dental category 6, upper facial height is not significantly different in male and female adult chimpanzees (dental category 7), in spite of the larger male body size, analogous to the condition recorded in humans. In the gorilla, both variables exhibit size dimorphism by dental category 4 and both traits are dimorphic in adults. Chimpanzee and human facial sexual dimorphism with respect to FHT are developmentally similar, and potentially explained by the same constraints of maxillary rotation and lower jaw development. This type of facial dimorphism, expressed as an index, was shown to be negatively correlated with canine height dimorphism across a taxonomically mixed sample of anthropoid primates, suggesting that there could be some kind of trade off between facial dimorphism (signalling attractiveness) and canine dimorphism (signalling aggression) [17]. If H. sapiens is included in the primate sample (see Materials and Methods, Table S2 and Figure S5), a significant inverse relationship is evident between facial and canine sexual dimorphism, with modern humans exhibiting low canine sexual dimorphism but sexually dimorphic faces. If facial structure replaced canine size, or perhaps the general possession of a large anterior dentition, as a sexual selection signal in early hominins [17], it would suggest that facial attractiveness did, indeed, play a major role in shaping human evolution.

Bottom Line: We consider sex differences in human facial morphology in the context of developmental change.A link between this developmental model and sexual dimorphism is made for the first time, and provides a new set of morphological criteria to sex human crania.This finding has important implications for the role of sexual selection in the evolution of anthropoid faces and for theories of human facial attractiveness.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University College London, London, United Kingdom. e.weston@nhm.ac.uk

ABSTRACT
We consider sex differences in human facial morphology in the context of developmental change. We show that at puberty, the height of the upper face, between the lip and the brow, develops differently in males and females, and that these differences are not explicable in terms of sex differences in body size. We find the same dimorphism in the faces of human ancestors. We propose that the relative shortening in men and lengthening in women of the anterior upper face at puberty is the mechanistic consequence of extreme maxillary rotation during ontogeny. A link between this developmental model and sexual dimorphism is made for the first time, and provides a new set of morphological criteria to sex human crania. This finding has important implications for the role of sexual selection in the evolution of anthropoid faces and for theories of human facial attractiveness.

Show MeSH
Related in: MedlinePlus