Beauty has been shown to be related to symmetry among other things. The more bilateral symmetry a person displays, the more physically attractive. Among the Masi warriors, those with the most bilateral symmetry can jump the highest, which the women find very attractive. Likewise, the more symmetrical the face, the more attractive it is considered. In addition, the proportions of the features to each other is considered more attractive the closer they follow the Fibonacci series, another ubiquitous type of symmetry found in nature.
All of this symmetry is an indication of healthy genes. Dwarves, for example, do not possesses the same ratio of length of limbs to body that is the most symmetrical in the fibonacci series. Likewise, the facial features of people with Down Syndrome do not follow this symmetry. In general, the more asymmetrical the body, the more damaged the genes.
Among humanity the health of our genes is of particular concern. Half of our DNA are what is sometimes called "junk DNA" that allows for extremely fast evolutionary changes and, recent evidence indicates, this is what distinguishes us from Chimps who otherwise share 98% of our DNA. Having the physical ability to evolve rapidly must be counter balanced by the ability to maintain a stable genome once an advantageous adaptation has been achieved. Hence the necessity for beauty, if not the desire for beauty.