Certain beliefs about beauty and notions of what is attractive have been explained by an experimental psychologist at the University of St Andrews in Scotland.
David Perrett, author of 'In Your Face: The New Science of Human Attraction', tweaks faces on screen to explore how they help us choose the best mates, reports the Sydney Morning Herald.
When someone smiles, we tend to think they are smiling at us, but when someone looks angry, we think they are mad at someone else, he says.
"One rule is symmetry - it does make faces more attractive. But it's a small factor. Another rule is averageness. That may seem contradictory, but we like to choose things that are familiar to us," he told The Los Angeles Times.
He added that making a woman's face more feminine (through software) may make it more attractive, but making a man's face more masculine won't have the same effect.
A face can covey a person's health too, he said.
"For instance, skin colour - this is not about dark skin or light skin, but rather about redness and yellowness. Ruddiness can tell you about the blood circulation, whether it's poor or good. Yellowness in the skin reveals a plant-based diet," Perrett said.
When asked about the role of symmetry in attraction, he replied, "Everyone seems to like symmetry, but not everyone likes it as much. For instance, women who find themselves attractive seek more symmetrical men. So the degree to which symmetry matters to someone depends on what they think of themselves."
"Symmetry is less important to some people; it actually explains very little about the range of attractiveness in people," he added.
Perrett explained that not everyone plays by the same rules or focuses on the same things.
"Beauty is in the eye of the beholder. The family - particularly parents - affects us. Especially if we get along with our parents, we tend to (but don't always) choose partners that resemble the opposite-sex parent," Perrett said.
"The experiences you have with someone - friendship, or more intimate - really affects how you see them. No matter what their face, the chemicals in our brain can lock us onto one person."
Perrett has written, "We're at our cutest at about 8 months of age, and after that it's all downhill."
He explained, "One way to chart this is to play around with faces of babies (on the computer). You can expand the forehead and reduce the size of the chin. By 8 months of age, human babies have a massive forehead and a really diminutive chin - and that's the point at which most people find babies most attractive."
"After 8 months, the face grows relatively quickly. That gives rise to a less and less cute configuration. We find infants cute and we want to take care of them," he said.
Perrett also dispelled the notion of 'sexy sons' - that good-looking sons will father the most offspring, and that what is attractive to women in one generation will be attractive to women in the next generation.
"We found that masculine dads do have masculine sons. But some women like masculine men and some women don't like it. So that's why there's no connection between father and sons," he said.
Which means that "a good-looking son could come from any dad, whether the dad was good-looking or not."