We compared the external morphology of primate eyes in nearly half of all primate species, and show that this feature is uniquely human. Humans have the largest ratio of exposed sclera in the eye outline, which itself is elongated horizontally.
We suggest that these are adaptations to extend the visual field by allowing greater eye movement, especially in the horizontal direction, and to enhance the ease of detecting the gaze direction of another individual.
The results revealed a striking difference between humans and apes. Human infants primarily followed the direction of the experimenter’s eyes, looking toward the ceiling nearly three times more often when he shifted only his gaze than when he merely raised his head with his eyes closed. In contrast, gorillas, chimpanzees, and bonobos relied mainly on head movement rather than eye direction. The apes looked toward the ceiling approximately 2.5 times more often when the researcher raised his head with his eyes closed than when he shifted only his gaze.
These findings indicate that humans and apes attend to different visual cues when determining where another individual is directing attention. Human infants are especially sensitive to eye gaze, whereas apes depend primarily on head orientation.
Humans are remarkably sensitive to eye contact and gaze direction.
Studies of newborn infants have shown that, within the first five days of life, babies look longer at faces whose gaze is directed toward them. The ability to follow another person’s gaze emerges between two and four months of age and becomes a consistent behavior by about eight months. Following another person’s gaze can reveal what interests them, where their attention is focused, whether they are being truthful, and can even help establish social bonds. Language is often complex and ambiguous, but eye contact provides an additional channel of communication.
In light of the fact that the human eye, with its highly visible white sclera, greatly enhances our ability to determine where others are looking, and what they are attending to. The important role that gaze detection plays in communication and social interaction rases an interesting question:
Q: if this trait provides such significant advantages, why is the conspicuous white sclera found only in humans and not in our closest ape relatives?
A: And God said, Let Us make man in Our image, after Our likeness: Genesis 1:26."
CEH
The results revealed a striking difference between humans and apes. Human infants primarily followed the direction of the experimenter’s eyes, looking toward the ceiling nearly three times more often when he shifted only his gaze than when he merely raised his head with his eyes closed. In contrast, gorillas, chimpanzees, and bonobos relied mainly on head movement rather than eye direction. The apes looked toward the ceiling approximately 2.5 times more often when the researcher raised his head with his eyes closed than when he shifted only his gaze.
These findings indicate that humans and apes attend to different visual cues when determining where another individual is directing attention. Human infants are especially sensitive to eye gaze, whereas apes depend primarily on head orientation.
Humans are remarkably sensitive to eye contact and gaze direction.
In light of the fact that the human eye, with its highly visible white sclera, greatly enhances our ability to determine where others are looking, and what they are attending to. The important role that gaze detection plays in communication and social interaction rases an interesting question:
Q: if this trait provides such significant advantages, why is the conspicuous white sclera found only in humans and not in our closest ape relatives?
A: And God said, Let Us make man in Our image, after Our likeness: Genesis 1:26."
CEH
