"The mirror test is a measure of self-awareness developed by Gordon Gallup Jr in 1970.
The test gauges self-awareness by determining whether an animal can recognize its own reflection in a mirror as an image of itself."
What Do Animals See in a Mirror?
"Gallup wasn't the first to come up with the notion that it might be significant if a person or animal recognizes itself in the mirror. He would only later learn that Charles Darwin had shown mirrors to orangutans, but they didn't figure the mirror out, at least while he was watching. Darwin had also noted that, for their first few years, his children couldn't recognize themselves in their reflections."