Most of the times, we associate symmetry with beauty. The symmetry may be in architectural/interior design for instance. Why would this be so ?
Indicator of genetic fitness argument
There is an evolutionary psychology argument. As with most evolutionary psychology arguments, the strength of the evidence is typically a bit fuzzy.
Symmetry in many aspects of the human body is functional. Such symmetry might be seen as the natural state that arises from a healthy life and a youthful body. In contrast various genetic abnormalities, diseases, and the like can give rise to asymmetry (e.g., scars, moles, freckles, ageing processes, deformities, etc.).
The argument might continue that it is adaptive for us to seek out sexual partners who appear genetically and environmentally fit where symmetry may be one indication of this fitness. One could even extend the evolutionary argument to suggest that it would be adaptive to avoid certain types of diseased individuals in order to reduce the risk of catching some disease, where various forms of asymmetry may be indicative of this.
How does this explain our desire for symmetry in physical objects? The perception of beauty in the environment might be seen as an extension of perceptions of beauty in other people.
Little and Jones also summarise this perspective
One explanation for the preference for symmetrical faces comes from a postulated link to an evolutionary adaptation to identify high-quality mates (see Thornhill & Gangestad (1999) for review). Symmetry in human faces has been linked to potential heritable fitness (‘goodgenes’) because symmetry is a useful measure of the ability of an organism to cope with developmental stress (both genetic and environmental). As the optimal developmental outcome of most characters is symmetry, deviation from perfect symmetry can be considered a reflection of challenges to development. Only high-quality individuals can maintain symmetrical development under environmental and genetic stress and therefore symmetry can serve as an indicator of phenotypic quality as well as genotypic quality (e.g. the ability to resist disease: see Møller (1997) and Møller & Thornhill (1998) for reviews). This logic would lead to a preference for high symmetry mates as evolution will have favoured individuals who had preferences for high-quality mates over low-quality mates. Indeed, morphological symmetry appears to be related to reproductive success in many species, including humans (Gangestad & Thornhill 1997a; Møller & Thornhill 1998). For example, more symmetrical human males have more sexual partners than less symmetrical men (Thornhill & Gangestad 1994) and symmetrical males are also more likely to be chosen as extra-pair partners (Gangestad & Thornhill 1997b). Thus the link between symmetry and attractiveness may reflect that preferences for symmetrical individuals may be potentially adaptive.
Enquist and Arak (1994) articulate a perceptual clarity argument. They wrote (my bolding):
Humans and certain other species find symmetrical patterns more attractive than asymmetrical ones. These preferences may appear in response to biological signals1–3, or in situations where there is no obvious signalling context, such as exploratory behaviour4,5 and human aesthetic response to pattern6–8. It has been proposed9,10 that preferences for symmetry have evolved in animals because the degree of symmetry in signals indicates the signaller's quality. By contrast, we show here that symmetry preferences may arise as a by-product of the need to recognize objects irrespective of their position and orientation in the visual field. The existence of sensory biases for symmetry may have been exploited independently by natural selection acting on biological signals and by human artistic innovation. This may account for the observed convergence on symmetrical forms in nature and decorative art.
- Enquist, M., Arak, A. & others (1994). Symmetry, beauty and evolution. Nature, 372, 169-172.
- Little, A.C. & Jones, B.C. (2003). Evidence against perceptual bias views for symmetry preferences in human faces. Proceedings of the Royal Society of London. Series B: Biological Sciences, 270, 1759-1763. PDF
There is a processing fluency theory that explains it quite nicely. In short, according to this theory the symmetrical objects are pleasant as they are easier to process.
See Reber et al (2004) for a detailed description:
We propose that aesthetic pleasure is a function of the perceiver's processing dynamics: The more fluently perceivers can process an object, the more positive their aesthetic response. We review variables known to influence aesthetic judgments, such as figural goodness, figure-ground contrast, stimulus repetition, symmetry, and prototypicality, and trace their effects to changes in processing fluency. Other variables that influence processing fluency, like visual or semantic priming, similarly increase judgments of aesthetic pleasure. Our proposal provides an integrative framework for the study of aesthetic pleasure and sheds light on the interplay between early preferences versus cultural infiuences on taste, preferences for both prototypical and abstracted forms, and the relation between beauty and truth. In contrast to theories that trace aesthetic pleasure to objective stimulus features per se, we propose that beauty is grounded in the processing experiences of the perceiver, which are in part a function of stimulus properties.
- Reber, R., Schwarz, N., & Winkielman, P. (2004). Processing fluency and aesthetic pleasure: is beauty in the perceiver’s processing experience? Personality and Social Psychology Review, 8(4), 364–382. doi:10.1207/s15327957pspr0804_3 PDF