I don't really agree. I believe in an idea of an Absolute Beauty that the trends cannot change. I would like to give an abstracter example like the golden ratio, but for now I would just give the example of the Nefertiti bust. She was beautiful then and she is still beautiful now. If you would see a woman with her features you would think that she is beautiful. (On the other hand,  there obviously exist trends and cultures. But it's only the spirit of the time and it doesn't really affect the Absolute :))

Depending on each person or specific cilture, the criteria for beauty may vary, however, there is at least a basic consensus beyond people or cultures about who is beautiful or not, I think.
Even a few month old babies recognize beautiful or handsome faces, and smile at them. Balance and harmony between body parts create good looks and it means good genes. So we humans including babies recognize beauty instinctly, because it is related to breeding and survival of our tribes. Animals are same.

Of course, the standards of beauty can be various according to cultures, times, and people.
However, I still think it's because each culture, era and person have different conditions and environments.

Nontheless, even though we are basically dominated by genetic Instinct, it isn't that it is always like that without exception. 

The standards of beauty prevail only at first. Later the attitude defines how the person looks for us. So I agree that beauty is always in the eyes of beholder.