The experience of "beauty" often involves an interpretation of some entity as being in balance and harmony with nature, which may lead to feelings of attraction and emotional well-being. Because this can be a subjective experience, it is often said that "beauty is in the eye of the beholder."
There is evidence that perceptions of beauty are evolutionarily determined, that things, aspects of people and landscapes considered beautiful are typically found in situations likely to give enhanced survival of the perceiving human's genes.
The classical Greek noun for "beauty" was κάλλος, kallos, and the adjective for "beautiful" was καλός, kalos. The Koine Greek word for beautiful was ὡραῖος, hōraios, an adjective etymologically coming from the word ὥρα, hōra, meaning "hour". In Koine Greek, beauty was thus associated with "being of one's hour". Thus, a ripe fruit was considered beautiful, whereas a young woman trying to appear older or an older woman trying to appear younger would not be considered beautiful. In Attic Greek, hōraios had many meanings, including "youthful" and "ripe old age". A study published in 2008 suggests that symmetry is also important because it suggests the absence of genetic or acquired defects.
Although style and fashion vary widely, cross-cultural research has found a variety of commonalities in people's perception of beauty. The earliest Western theory of beauty can be found in the works of early Greek philosophers from the pre-Socratic period, such as Pythagoras. The Pythagorean school saw a strong connection between mathematics and beauty. In particular, they noted