When you make that first instantaneous judgment about whether or not you like how someone looks, you're actually being influenced by a whole slew of things you don't realize you find attractive. At first glance, the basics of attractiveness seem pretty straightforward - humans like health and youth because they like reproductive fitness. Generally, humans also like sexual dimorphism (men with strong jaws and large brows; women with large eyes and youthful features). None of that should be too surprising. Humans are pretty predictable in this respect, and they really aren't much different from the lowliest bug who desperately wants to mate with whichever other bug would enable it to procreate the best.
That's how it seems at first glance, anyway. Beneath the obvious stuff, a lot of other cues determine whether you like what you see when you look at someone's face, and we waste no time in making that determination. It takes about a tenth of a second for you to see a face and jump to a whole bunch of conclusions - whether the person is trustworthy or not, aggressive or not, and, obviously, whether he or she is attractive. But if you were to write down a list of the things that you assume you find attractive, and then read this list, you will probably not find much overlap. From the smell of someone's sweat to the amount of vegetables a person eats, there are tons of features we're attracted to without knowing it.
Men With Wide Faces Come Across As More Sexually Fit
Several traits are associated with facial width; for example, men with wider faces have higher levels of testosterone than average (and also, as a corollary, higher levels of aggressiveness). A higher facial width-to-height ratio ("fWHR ") is seen as more dominant and powerful. Women also consider these men more attractive - at least, as short-term romantic partners, not necessarily as long-term marriage prospects. A speed-dating study found that women expressed more interest in men with a high fWHR and were more likely to want a second date with them. (This is a distinction the researchers noted; the women didn't just find these men more attractive; they were actually willing to pursue real-world interactions with them, as opposed to just rating their appearances in an experimental setting.)
Averageness Is An AphrodisiacDescriptions of beauty always focus on someone's outstanding features: her big, soulful eyes or his chiseled jaw. Nobody ever writes an attractive character by saying "Well, to be honest, most of her was pretty unremarkable." But all of a person's ordinary features, the ones that don't really stand out, are actually pretty important. Several studies have demonstrated that, the less a person's features differ from the norm in a given population, the more attractive his or her face is. One study found that averaging together random faces into a composite image resulted in a more attractive face than any of the individual source faces.
Immune System Strength Is A Turn On
Given that human immune systems have the ability to distinguish between their own cells and the cells of another person, it shouldn't come as a surprise that one of the unseen forces of attraction is the health of someone's immune system. British researchers tested the immune systems of male subjects by measuring their antibody responses to a vaccine for Hepatitis B. They then showed photographs of the men's faces to 94 female study participants, who went on to rate the men with the strongest immune systems as more attractive than their peers. (The men rated as most attractive also had higher testosterone levels and lower levels of the stress hormone cortisol.) Incidentally, this seems like it may be a one-way correlation; a similar study by the same researchers found that men also preferred the faces of women with low cortisol, but their immune systems weren't significant to facial attractiveness ratings.
Men Love A Long-Armed Woman
A study in the Journal of Evolutionary Biology found that some aspects of attractiveness were to be expected, and they persisted across different cultures. When asked to rate images of various women for attractiveness, a group of Australian participants pretty much agreed with a group of Hong Kong participants in their ratings; both groups prioritized things that indicate youth and health. Both groups preferred taller women with a low BMI and a high hip-to-waist ratio. Surprisingly, though, both groups also indicated a preference for women with longer arms; leg size had no effect on their ratings.