Can we blame our fear of the dark on our ancestors? MAYBE!
Being afraid of the dark is known as a "prepared fear." Martin Antony, professor of psychology at Toronto Metropolitan University said, quote, “I would see a fear of the dark as what we call a prepared fear. What that means is we’re prepared or predisposed to develop fears of some things more than others.”
These "prepared fears" go back to what would have been dangerous to our prehistoric ancestors. There are other factors that could also contribute to this fear like: certain life events & fear of the unknown.
Source: HuffPost