One thing that I have conclude is that ideal beauty is partially naturally based in the sense of symmetry and such, but that ideal beauty is even more so socially based.
On that note, it is my opinion that society's ideal beauty is based on wealth and how money and power can attribute to a person's look.
For instance, before the 20th century, the ideal western woman was pale, plump, and had very little muscle. Only wealthy women could achieve this look because they could afford not to do heavy labor and could afford to eat heartily. The middle to lower class woman would have had tanner skin, muscular arms, and would have been thinner due to lack of nutrition.
But since the 20th century, this trend has flip flopped. Now tan skin and very thin waists are a sign of ideal beauty, and this flip happened because in the past 75-100ish years for only wealthier women can afford this look. The industrial revolution forced a movement towards more desk-related or indoor jobs rather than physical labor for the middle to lower classes, and so the middle to lower classed women tend to be paler, plumper, without toned arms. They don't have the money to spend on tanning salons or vacations to exotic beaches, don't have time to go to the gym or money to pay for a membership, and are often exposed to unhealthier eating habits by eating more processed foods and eating at fast food restaurants.
At the same time though, It's a slightly different story when it comes to race. I've read articles about arguing how in the media paler women give off the image of pureity and female strength and are more goddess-like, and tanner women give off the image of sexiness and seduction. Tanner women in the media are more likely to be wearing less clothing than paler women. I realize there are a lot of factors that could be playing into this study such as race... but it was an interesting read.
I have noticed that when I go into the makeup aisle at Jewell, the pictures were all of black or mixed race black/white women who had paler chocolate skin to begin with that were lighted to look even more white. The 3 I saw were Jessica Alba, Halle Berry, and Beyonce Knowles. All three of them are drop dead gorgeous, but they are black women with whitish features. In this way the make up companies are trying to appeal to women of color by using black women as their models, but also to white women because all three have very white features that are heightened and highlighted in the advertising. It makes perfect sense, but I feel almost tricked in a sort of way.... it's a very backhanded way to say that darker skin and black features are undesirable.