The Emergence of Self-Awareness: The Mirror Test
Do other animals have a sense of self?
One common way of answering this question is with the "mirror test". Does an animal recognize itself in a mirror?
The test was first devised by Charles Darwin who held up a mirror to an orangutan in a zoo, noting how the animal reacted with unusual facial expressions. In the 1970s the test was refined by placing a mark on an animal's face, and then observing how it responded when it looked in the mirror. Orangutans, chimpanzees, gorillas and bonobos will poke the spot or try to remove it, showing that they see the image in the mirror as a reflection of themselves. Bottlenose dolphins and orcas also pass the test. And recently elephants have been shown to pass it.
Dogs and cats, however, fail the mirror test. Dogs will occasionally bark at their reflection, and cats have been known to go look behind the mirror, but generally these animals ignore their image in the mirror. It is therefore assumed that they have no sense of self. But can we draw such a clear line between creatures with a sense of self and those without?
That a dog or cat generally ignores its reflection rather than behaving as if it were seeing another animal is interesting. They do not pass the test in the sense of recognizing themselves in the reflection; yet they do not completely fail the test either. They know they are not seeing another dog or cat. I call this "not-other" awareness, as opposed to full self-awareness.
I suspect not-other awareness is to be found in any animal that drinks from water. As it leans forward to drink, it is likely to come face to face with its own reflection. If it interpreted this as another animal looming close, it would probably back off (and, if repeated continually, die of thirst). For such creatures, there is a clear evolutionary advantage in the inhibition of the "other" response when seeing their own reflection in water.
With the great apes, dolphins, and elephants, consciousness has now evolved to the point where it can recognize the "not-other" as itself.
So it would seem that the evolution of self is not a black or white affair. There are many shades of gray between no self-awareness and self-awareness.