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Here are a few more scientific studies which could pass for the more outlandish claims of The GenoType Diet. Finger digit ratios (the comparison of the lengths of the ring and index fingers) correlate with other facial structures used in The GenoType Diet, such as jaw angle and other asymmetries. Put it all together and you get (drum roll, please):
The second-to-fourth-digit ratio (2D:4D) may be related to prenatal testosterone and estrogen levels and pubertal face growth. Several studies have recently provided evidence that 2D:4D is associated with other-rated facial masculinity and dominance, but not with facialmetric measures of masculinity. We found that localized face shape differences, shown here to be sexually dimorphic* and related to ratings of dominance, were associated with direct and indirect measurements of 2D:4D. In this study we examined various localized features of the face, showing nose width, jaw angle, and lip height to be sexually dimorphic. We then had faces rated for dominance and saw that the most dimorphic characteristics were those most associated with rated dominance, with typically masculine characteristics tending to be associated with high ratings of dominance. Finally, 2D:4D measurements were made using three different techniques. High (feminine) values of 2D:4D were associated with feminine facial characteristics in women, but not in men. It was concluded that certain aspects of facial development are governed by factors that are established prenatally. These aspects may be associated with perceptions of the self by others that are important in the social environment, particularly in terms of intra-sexual competition and mate acquisition.
* Dimorphism is the systematic difference in form between individuals of different sex in the same species.
2D:4D and sexually dimorphic facial characteristics. Arch Sex Behav. 2007 Jun;36(3):377-84.
The average human male face differs from the average female face in size and shape of the jaws, cheek-bones, lips, eyes and nose. It is possible that this dimorphism is determined by sex steroids such as testosterone (T) and oestrogen (E), and several studies on the perception of such characteristics have been based on this assumption, but those studies focussed mainly on the relationship of male faces with circulating hormone levels; the corresponding biology of the female face remains mainly speculative. This paper is concerned with the relative importance of prenatal T and E levels (assessed via the 2D : 4D finger length ratio, a proxy for the ratio of T/E) and sex in the determination of facial form as characterized by 64 landmark points on facial photographs of 106 Austrians of college age. We found that (i) prenatal sex steroid ratios (in terms of 2D : 4D) and actual chromosomal sex dimorphism operate differently on faces, (ii) 2D : 4D affects male and female face shape by similar patterns, but (iii) is three times more intense in men than in women. There was no evidence that these effects were confounded by allometry or facial asymmetry. Our results suggest that studies on the perception of facial characteristics need to consider differential effects of prenatal hormone exposure and actual chromosomal gender in order to understand how characteristics have come to be rated 'masculine' or 'feminine' and the consequences of these perceptions in terms of mate preferences.
Second to fourth digit ratio and face shape. Proc Biol Sci. 2005 Oct 7;272(1576):1995-2001.
Sex steroids are supposed to moderate the differences between male and female facial characteristics. Studies on women's preferences for male faces reported increased preferences for facial architecture developed under the influence of testosterone as this may indicate masculinity, dominance and social status. Recent research demonstrates that facial sexual dimorphism does not only develop at puberty but may be organized much earlier in ontogeny. However, the actual cause and timing of variation in facial shape due to sex-steroids remains speculative. This study uses data from Neave and colleagues who measured digit ratio (2D:4D) as a proxy to prenatal testosterone and also salivary testosterone samples in order to study differential effects of androgens on perceived male facial shape. Male facial shape was regressed upon 2D:4D ratio and circulating levels of testosterone by means of geometric morphometric methods. We found some evidence for opposite effects of early androgen action (via 2D:4D ratio) on the upper and the lower face respectively (i.e. low 2D:4D ratio results in a relatively robust and prominent lower face), whereas circulating testosterone seems to cause a rather uniform elongation of the face. Local deformations primarily show pronounced and medially tailed eyebrows for the shapes associated with increasing salivary testosterone. These preliminary results suggest that prenatal and pubertal testosterone have differential effects on male facial shape that should be considered in future studies on women's preferences towards male facial appearance.
Visualizing facial shape regression upon 2nd to 4th digit ratio and testosterone. Coll Antropol. 2005 Dec;29(2):415-9.
Deviations of physical characteristics from bilateral symmetry, in otherwise symmetric individuals, are supposed to result from environmental perturbations during development. One cause of such perturbations may be sex steroids such as testosterone and estrogen. AIM: The study examined the relationship between second to fourth digit ratio (2D:4D), a putative negative correlate with prenatal testosterone and a positive correlate with prenatal estrogen, and asymmetry. METHODS: Eleven traits (including the second and fourth finger lengths) were measured in a sample of 680 English children aged 2-18 years, and second to fifth finger lengths in samples of 120 Austrian and English undergraduate students aged from 17 to 30 years and 213 Polish adults aged from 26 to 90 years. RESULTS: Significant U-shaped curvilinear associations between 2D:4D and all 11 traits were found in English children with the strongest associations between 2D:4D and composite asymmetry of second plus fourth digit, and second to fifth digits. Further investigation of the relation between 2D:4D and digit asymmetries in the sample of Austrian and English undergraduates and the Polish adults confirmed significant U-shaped relationships between 2D:4D and finger asymmetries. CONCLUSION: Our data show that both low 2D:4D (a marker of high prenatal testosterone) and high 2D:4D (a marker of high prenatal estrogen) are associated with elevated levels of asymmetry and this relationship applies particularly to finger asymmetry.
The second to fourth digit ratio and asymmetry. Ann Hum Biol. 2006 Jul-Aug;33(4):480-92.
I just saw the documentary "Encounters at the End of the World" by Werner Herzog and in the film he interviews a man who is part American Indian (can't remember what tribe) who has some very interesting fingers. His D2 is exceptionally short (such that the DIP of D2 is in line with the PIP of D3!) and his D4 is exceptionally long (such that it matches D3). Overall, this means that when he adducts his fingers, D3 and D4 are identical and D2 and D5 on either side are identical and it forms a symmetrical shape. According to him, this is a feature of Aztec descendents.
I'm assuming that this must either be a specific genetic trait of Aztecs or some strong epigenetic influence that pushes the D2:D4 ratio extremely low.
Needless to say, this was the most interesting part of the whole film for me and so I've been trying to find into about this feature with no luck. I was just wondering if you have seen/heard of this before and if you know where I can go read more?
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