Symmetry Predicts Sex-typical Body Attractiveness

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Symmetry Predicts Sex-typical Body Attractiveness

SciMed - Neuroscience

TS-Si News Service

Wednesday, 20 August 2008 16:30

Dr. William Brown and colleagues at the Brunel School of Social Sciences and School of Engineering and Design used a 3D optical body scanner to accurately measure human body proportions.

Genotype & Phenotype. Every living organism exhibits the outward physical manifestation of its internally coded, inheritable information.

A genotype is the internally stored set of instructions (the blueprint) for building and maintaining a creature throughout its life. Nearly all cells contain the instructions in a language called the genetic code).

The bluprint is inheritable because it is copied at the time of cell division or reproduction, then passed from one generation to the next. These instructions are intimately involved with all aspects of a cell or organism, controlling everything from the formation of protein macromolecules to the regulation of metabolism and synthesis.

The genetic code is stored on one of the two strands of a

DNA molecules. It is a linear, non-overlapping sequence of the nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C) and Thymine (T). The alphabet, AGCT, is used to write a sequence of three letter code words (triplets or codons). There are 64 code words possible from an alphabet of four letters.

Each 3-letter code word can be interpreted as a single amino acid in a polypeptide chain, a sequence of words along the length of the DNA strand. The start signal word begins all sequences coding for amino acid chains; three words are stop signals that close the message.

All the other sequences code for specific amino acids. Some amino acids are only coded for by a single 'word', while some others are coded for by up to four 'words'. The genetic code is redundant.

A phenotype is the physical manifestation of an organism — the outside. The living organism is the sum total of its physical parts. They include anything that is part of an organism's observable structure, function or behavior (atoms, molecules, macromolecules, cells, structures, metabolism, energy utilization, tissues, organs, reflexes and behaviors).

The relationship is direct: the genotype codes for the phenotype. The internally coded and inheritable information, the genotype, holds the critical instructions that are used and interpreted by the cellular machinary of the cells to produce the outward, physical manifestation, or phenotype of the organism.

The molecules, macromolecules, cells, and other structures act and interact with one another over time, producing larger and more complex phenomena (such as metabolism, energy utilization, tissues, organs, reflexes and behaviors).

A genetic trait is a small part of an organism's phenotype. The tools of molecular and cellular biology can see into the cell cytoplasm and observe chemical reactions that result in the ever more complex structures obervable to our eyes. The action of proteins produces almost all traits.

The information flow insures a a trait can be observed. DNA molecules store the essential instructions for building a protein macromolecule. These instructions are copied from the DNA molecule into the form of an RNA molecule. One, or many copies can be made of these instructions.

Each of these messenger RNA (mRNA) copies move away from the DNA templates and enter the cytoplasm of the cell. They then encounter the machinery that will convert the biological information (the instructions) into the correct linear sequence of amino acids that will become a functioning protein.

Once the protein has been correctly assembled and folded it can go to work and produce a particular trait.

Uxbridge, Middlesex, UK. Scientists used a breakthrough methodology that reinforces sexual dimorphism with objective measures of what makes the human body attractive. The first 3D study identifies masculine traits associated with the attractiveness and symmetry of male and female bodies, explaining why symmetry predicts bodily attractiveness.

Brunel University scientists have developed an explanation for the correlation between attractiveness and bodily characteristics like height, broad shoulders, long legs, breast size, or a curvy figure.

[ Download Supp Data PDF ] [ Download Movie Zip ]

The study also explored the degree of asymmetries between the left and right sides of the body. It is widely believed that for many species, including humans, asymmetry is an indirect measure of developmental quality. The findings appear in the Proceedings of the National Academy of Sciences (PNAS).

Dr. William Brown and colleagues at the Brunel School of Social Sciences and School of Engineering and Design used a 3D optical body scanner to accurately measure human body proportions. [Note]

Through their research at the Brunel Centre for Cognition and Neuroimaging (CCNI), Brown and his team identified a property dubbed ‘body masculinity’.

The property is a mathematical fusion of several traits, including greater height, wider shoulders, smaller breasts and shorter legs.

The study co-author, Dr. Jinsheng Kang from Brunel’s School of Engineering and Design, explained the methodological benefits of this new technology:

The 3D body scanner accurately extracts hundreds of measurements of the human body, including volume, in six seconds and removes a potential source of measurement error, the human experimenter.

Previous studies of this kind relied on callipers to measure body traits, which are highly prone to human error and can only measure up to a maximum of nine inches, thus missing important 3D aspects of size and shape.

Researchers used the 3D optical scanner to characterise the bodily topography (size and shape) of 77 volunteers (40 male and 37 female). Other volunteers then assessed how attractive the bodies of the opposite sex were, in a colour-neutral, 360 degree computer-rendered videos, minus the heads.

Key findings of the study included:

When asked to assess the attractiveness of female 3D body images, men rated those with less body masculinity most attractive, and vice versa
High masculinity correlated with fewer departures from perfect bodily symmetry in males but with more asymmetry in females.

This suggests that those with good development and health may have bodies that exaggerate sex-typical bodily features.

Commenting on the research, Dr. Brown says “It is widely believed that human beings are attracted to one another as a result of genotypic and phenotypic quality — in other words, their prospect as a mate who will yield higher quality offspring for the chooser.”

“My previous research suggested that bodily symmetry is not necessarily what people attend to when they find someone attractive but nonetheless the physical cues that they do prefer may reveal an individual’s underlying developmental quality (i.e. degree of symmetry)."

"This new research identifies an explanation for the correlation between bodily shape and attractiveness:

your body proportions, shape and stature are signals that conspicuously advertise your good development or health and therefore the degree to which you are a desirable reproductive partner.

In many species fewer departures from perfect symmetry are associated with good development, health and reproductive success.”

He concludes: “It seems that because bodily asymmetries are too subtle to be seen with the naked eye,

evolution has instead engineered more conspicuous signals and displays, such as broad shoulders, curvy waist lines or smooth dance moves to indicate mate quality.”

[Note] Brunel’s 3D body scanner was purchased by grant funding awarded to Professor David Wright and assistance from the School of Engineering and Design.

Fluctuating asymmetry and preferences for sex-typical bodily characteristics. William M. Brown, Michael E. Price, Jinsheng Kang, Nicholas Pound, Yue Zhao, and Hui Yu. PNAS 18 August 2008. doi: 10.1073 / pnas.0710420105.
[ Download Supp Data PDF ] [ Download Movie Zip ]

Abstract

Body size and shape seem to have been sexually selected in a variety of species, including humans, but little is known about what attractive bodies signal about underlying genotypic or phenotypic quality. A widely used indicator of phenotypic quality in evolutionary analyses is degree of symmetry (i.e., fluctuating asymmetry, FA) because it is a marker of developmental stability, which is defined as an organism's ability to develop toward an adaptive end-point despite perturbations during its ontogeny. Here we sought to establish whether attractive bodies signal low FA to observers, and, if so, which aspects of attractive bodies are most predictive of lower FA. We used a 3D optical body scanner to measure FA and to isolate size and shape characteristics in a sample of 77 individuals (40 males and 37 females). From the 3D body scan data, 360° videos were created that separated body shape from other aspects of visual appearance (e.g., skin color and facial features). These videos then were presented to 87 evaluators for attractiveness ratings. We found strong negative correlations between FA and bodily attractiveness in both sexes. Further, sex-typical body size and shape characteristics were rated as attractive and correlated negatively with FA. Finally, geometric morphometric analysis of joint configurations revealed that sex-typical joint configurations were associated with both perceived attractiveness and lower FA for male but not for female bodies. In sum, body size and shape seem to show evidence of sexual selection and indicate important information about the phenotypic quality of individuals.

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Last Updated on Wednesday, 20 August 2008 16:45

TS-Siis dedicated to the acceptance, legal protection, and medical treatment of individuals correcting the misalignment of their brains and their anatomical sex, while supporting their transition into society as hormonally reconstituted and surgically corrected citizens.

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