Not just the windows to the soul: our eyes can reveal more about us than previously thought.

The human eyes are often referred to as the "windows to the soul" or "mirrors of the soul," but a new study by researchers suggests that our eyes may reveal much more about us than previously thought. The study indicates that it's not just about the color of our eyes, but also two other crucial factors, as reported by Daily Mail.

The research was conducted by scientists from Leiden University. The team discovered that our eyes significantly influence how people perceive everything around us, from our attractiveness to our generosity.

While one might think it's solely about the color of our eyes, the researchers emphasize that two other important factors are: pupil size and iris brightness. During the study, participants were asked to evaluate photographs of non-human primates with altered eyes.

The study's findings revealed that animals with bright irises and large pupils were rated by participants as more attractive and friendly. The team also found that animals with larger pupils appeared more appealing to people.

According to the authors of the study, their results demonstrate that minor changes in the perceived morphology of the eyes affect behavior and emotional responses. The human eye is composed of several parts, including:

• the iris;
• the pupil;
• the lens.

Most previous studies have looked at the effects of each of these parts in isolation. For instance, a prior study found a link between pupil size and traits such as friendliness, attractiveness, and trustworthiness. However, in this new research, the scientists aimed to determine whether changes in both pupil size and iris brightness affect how we are perceived by others.

According to lead author Juan Olvido Perea-Garcia, in the first experiment, 64 participants were shown portraits of 32 species of non-human primates, including chimpanzees, lion tamarins, and silvery gibbons. The animals' eyes were adjusted for pupil size, with some having larger pupils than usual and others smaller. Participants were then asked how much money they would be willing to donate for the conservation of each species, as well as how cute, friendly, and attractive they found the animal in the photo.

The results indicated that people donated more when shown animals with larger pupils. They also rated the animals as cuter, friendlier, and more attractive when they had larger pupils.

The second experiment involved 121 individuals. They were also shown photographs of non-human primates, but this time the researchers adjusted the brightness of their irises as well as pupil size. This time, the researchers found that participants donated more when they were shown eyes with brighter irises. They also perceived primates with brighter irises as cuter, friendlier, and more attractive, but only if they had dilated pupils.

Now, researchers believe that pupil size is key to our perception of people, although iris brightness seems to play an important role as well.