At the beginning of the video starring Marcus de Sautoy, he observes Gordon Gallup's mirror self-recognition experiment in person. In this experiment, the parent of a child sticks a black dot to the child's face without them knowing, disguised by them blowing their nose. Then, the child is put in front of a mirror. If they acknowledge the dot on their face, it proves they are self-aware.
When Sautoy was observing this experiment in action, he watched it being performed on two individuals. Owen was 16 months old and Bethany was 22 months old. When the dot was placed on Owen's face, he did not see himself in the mirror and recognize that there was something on his face. But when the dot was placed on Bethany's face, she did notice that there was something on her face via the mirror and tried to remove it. This concludes that Owen was not self-aware, but Bethany was. By doing this experiment, scientists have been able to narrow the window of time in which we become aware of ourselves to between 18 and 24 months of age.
Gallup also thought about how this experiment would work on animals. Out of all the animals he tested, only chimpanzees and orangutans were able to pass the test like humans. This video isn't showing this experiment, but it is showing how chimpanzees are aware of themselves in a mirror. This feat distinguishes the great apes (chimps, orangutans, and humans) from all other animals. This self-awareness allows us to "mentally time travel" so that we can think about what we've done in the past, what we are doing in the present, and what we could be doing in the future. The downfall of being self-aware is that we are also aware of the death of our consciousness.
After watching this video and seeing this experiment, I find it quite fascinating that we become self-aware at such a young age. I would have thought we'd need to be much older to recognize this. If we are aware of ourselves at such a young age, how come we can't remember memories from that young, too?