Quote from a very interesting paper on human sleep (ecology of human sleep):

Fire also produces steady, irregular (in volume, frequency, and quality) noise that some ethnographers report as being subliminally monitored in sleep: continual small noises are reassuring, loud pops are arousing, and the absence of sound wakes the sleeper concerned with fire maintenance.

Why do we need total darkness? Haven't humans mastered fire for hundreds of thousands of years? Personally I have no problem sleeping during the daytime. Remember also that the moon provides a little light during night as well.

I'd say that most sleep problems are due to people staying up late. It's not like ancient humans had laptops, televisions, and other electronic stimuli.

I've never had a problem with noise preventing me from sleeping. I grew up on a farm, and there would regularly be koalas fighting outside my bedroom window, rifles firing at foxes in the distance, my Dad watching TV late into the night (between lamb feedings), and other bumps in the night. When I moved into the city, my computer would hum so much that others couldn't bare to sleep near it. I never noticed.

Needing darkness makes sense, especially on a hormonal level. But nighttime isn't quiet, so it doesn't make sense to need perfect silence. However, our survival instincts probably mean that our subconscious is attuned to particular 'danger' noises that may lighten or disrupt our sleep. So if you live in a neighbourhood where people scream at all hours, dogs barks, etc, then perhaps a brown noise machine or other sound blocker is a sensible choice.

Untill very recentlly people rarely slept separate from others, this is still true in many parts of the world. The extented famnily or even the entire tribe of maybe upto 50 people would have slept in close proximity, everyone from the babies to the elderly.

Historically the most normal night-time environment of a cave or hut would have been filled with the sounds of people breathing, snoring and having sex. There would be young babies being breast-fed and comforted, people waking up, squashing biting insects, tending to the fire and talking quietly.

If sleeping out in the open these would be added to by the sound of the wind, insects chirping, animals and birds calling and rodents russling in the grass.

In the wild a restfull nights sleep would be aided most by the feeling of security of knowing you're surounded by relatives with less risk of being draged off and eaten by lions coming out of the darkness.

I'd say some noise is quite normal.

Try sleeping outdoors, near a river. You think there's anything such as silence in a typical, evolutionary human environment? The night is loud with cascading, burbling sounds... of water, insects, frogs, birds, etc. White noise is evolutionarily appropriate for sleep. In fact, for millions of years, every night sleeping creature most likely slept in the midst of nocturnal sounds.

Nature isn't all that quiet so I'm not sure that's equivalent to darkness. I think you're on the right path with your "brown noise", though. White noise masks lots of low-volume sounds neurologically (if I recall my undergrad psychology classes correctly) so it would help with small disturbances but not the loud ones - which you might want to hear for your own safety!

I think most people can adjust to various levels of noise during sleep. My favourite noise is water- either a river or stream or ocean, and even a rainstorm will do.

In Mexico we adjust to fireworks at odd hours of the night, roosters crowing at inappropriate times, church bells before the crack of dawn, and loud music just as a few examples.

Previously when I lived near an airport I became adjusted to hearing planes at all hours and the noise quit affecting my sleep.

One of our friends keeps the radio on all night to sleep well, whereas his wife used to use a clock radio as an alarm and she now has trouble getting restful sleep, so I guess some people adjust more easily than others.

I usually use my oscilating fan. Turn it on medium or high, puts me right to sleep. So does the sound of rain or the rumble of an engine.

I was stationed on a river tender a while back and when we were underway, the 2 caterpillar engines would put me right to sleep, but keep everyone else up. Haha.

There are downloads of white noise sound files that are for specific purposes. Cat naps, deep sleeps, etc.; basically subliminal messages to our brain. Pretty interesting, but I've only used them a time or two.

I use earplugs every night without fail. Every now and then I try going to sleep without them, but my sleep is not as restful and it seems to take longer to hit deep sleep.

My very best sleep is when I am camping. I think it could be due to many factors like the sounds of water from rain, rivers, and the ocean. More active during camping also no electronic stimuli helps to fall asleep. One time I was scared of bears while camping with my son in a tent, so I DID NOT get any sleep that night. I think the security factors in as well as mentioned.

At home every little noise bother's me and I need to use ear plugs to help me stay asleep. I can do this now that my kids are older, but I did not use them when they were young.