Science can’t determine values, and this includes aesthetics, beauty. But that doesn’t mean science has nothing to say about beauty. As this article at PolicyMic indicates, it can study what most of us see as beauty and explore the reasons why we see it as beautiful.
The primary reason we are alive is to reproduce and pass our genes onto the next generation, who then reproduce and pass their genes on, and so on. But in order to give our children the best chance of surviving long enough to reproduce, we are wired to choose the healthiest partner we can find — and beauty is often the best proxy for health.
As science writer Matt Ridley explains in his book The Red Queen, “Prettiness is an indication of youth and health, which are indications of fertility. Why does [a] man care about fertility in his mate? Because if he did not, his genes would be eclipsed by those of men who did.”
But I think it would be wrong to conclude from this that beauty is solely a biological or evolutionary function. In the case of humans, the biological markers of health and fertility are required, but not sufficient. They provide a range of possibilities of what we might find beautiful.
Culture is what further restricts our conception of beauty, just as it restricts our conceptions of morality from the options our biology provides. It’s why many may not consider people from other cultures attractive, or ethnic groups discriminated against in their culture as desirable. Even a liberally minded person raised in a certain culture may not have a primal feeling of attraction to what another culture regards as beautiful.
I think the right way to think of it is that, for most people, both the biological instinctive triggers and the local cultural requirements must be met for beauty to be appreciated. Insisting that it be one or the other is a false dichotomy.