I don't understand what you mean. The ancestral environment is one in which danger comes at night; that's when the tigers come for you. That's why people ar

I don't understand what you mean. The ancestral environment is one in which danger comes at night; that's when the tigers come for you. That's why people are afraid of the dark, why even grown men run up their basement stairs after turning off the lights. Monsters in the dark will nip at your heels; that's what our genes tell us. But in the modern context, a child who's facing real adversity (not monsters under their bed) at night has serious problems with their home-life which they'll be poorly equipped to deal with. Daytime problems for kids are usually problems with other kids and teachers, but those kinds of problems are much easier for kids to deal with alone. Particularly if their home situation is stable.