comment: >
  
  I guess that's why some people wake up easier. And why there is a difference between morning people and evening people/night owls. Insures someone is awake to either hear or see a threat and can alert others. At least that would made sense in times before.
  Also heard people in the middle ages slept close together. Like only a room away or even closer. Safety in numbers I guess.
context: This is a friendly reminder to read our rules.
  Remember, /r/Showerthoughts is for showerthoughts, not "thoughts had in the shower!"
  (For an explanation of what a "showerthought" is, please read this page.)
  Rule-breaking posts may result in bans. >
  
  Like other mammals, humans live in groups and have security systems that protect the group.  Like a locked door.  Or 500 years ago, someone in the village or tribe that slept in the day and was awake at night. >
  
  That's probably why some people have a intrinsic tendency to wake up really early while others are the opposite. Diversity within a group probably worked as some sort of defence mechanism. Nowadays we are just lazy when we have a hard time going to sleep early/waking up early. :) >
  
  There is indeed a theory proposed a number of years ago in psychology and sociology which speculates that the reason older people tend to have more trouble sleeping and require less sleep per night has to do with exactly this. The idea being that older people are more likely to nap during the day when the younger portion of  the village would be busy doing tasks and chores that older people are less able to do. Then, at night, older people are more easily awakened by external threats like animals, invaders, or impending natural disasters and would then go about rousing the people to counter or escape the threat. 
  They also pointed out men tend to wake more easily to when disturbed by sounds with bass and tend to lose more high frequency hearing range as they age. Women tend to be more readily awakened by higher pitch sounds like a baby crying, and tend to lose more in the lower frequency ranges as they age. 
  I wish I could provide a source on this but I do not remember which podcast I was listening to at the time. I can only say that it was around 2018 and I was doing a ton of research on sleep disorders, sleep apnea, PAP therapies, and generally all things having to do with sleep hygiene when I came across a podcast with a research scientist talking about it from a historical/evolutionary perspective. I've never been able to find a paper about this online despite having looked again just now. 
  It seems very plausible though, considering that, in the past, many generations often lived with each other and this would have niched the roles somewhat. >
  
  My personal take away from this is that humans weren't meant to survive alone but as part of a community. >
  
  The only thing we have going for us that isn't related to living in groups is our ability to chase anything to death >
  
  Also throwing! No one throws like a human. Our hunting game went to another level when throwing spears got involved. >
  
  And even MORE extreme when we learned how to throw sharp rocks SUPER fast through a metal cylinder by using gunpowder >
  
  We basically got really good at throwing rocks >
  
  Deadly yeets >
  
  Many animals have existed much longer than humans and are the same way. Yet to see a dog or wolf or bear spray acid from its ass as a defense mechanism and remain asleep after. Because that self-defense mechanism is called "waking up" >
  
  You were so close. One could say that domestication of dogs was our way of evolving our self-defense while sleeping. >
  
  One could say it, sure.... Wouldn't make much sense tho. >
  
  This doesn’t really make sense. By your logic, couldn’t someone just argue that we’ve actually evolved so greatly on other levels (technologically, engineering, etc) that we now have the luxury of being totally vulnerable while we sleep because we’ve created safety systems like enclosed domiciles? Isn’t that just a perfect example of evolution? >
  
  OP doesn't understand evolution >
  
  That's made clear by their implication that 200,000 years is even remotely meaningful in evolutionary terms. >
  
  I actually didn’t even think of that but you’re beyond right >
  
  200k years is a blink in terms of evolutionary timelines >
  
  Depends on the species. Some bacteria evolve so quickly that it's the cause of antibiotics failing. >
  
  In the ancient past, it was called a watch. Each watch was 3 hours then rotated to the next person on watch.  But you're right though. We sleep more soundly in modern times. >
  
  Reminds me of ftxs in the army. Or missions in general >
  
  Bro why you getting down voted LMAO >
  
  Idk it's true.
  Someone stays up guarding SI, or even in garrison they watch the building aka staff duty or cq. Then they get a rest day after. >
  
  All animals are vulnerable while they sleep. Some sleep in holes in the ground, others sleep in trees. Some sleep in packs. Humans alarm their town houses and keep baseball bats by the bed >
  
  This post complexity misunderstands what evolution is. Evolution is not some ordered system that tries to solve problems or “improve” the species. It’s the result of completely random mutations that just by chance happen to provide some benefit, such that the individuals with that mutation are more likely to live and pass it in to future generations.
  Humans haven’t evolved some specialized defense mechanism during sleep because either: the random mutations just never happened or some mutations happened but they provided no added survival benefit beyond what the rest of the species had.
  Edit: added some clarification >
  
  Yeah OP acting like we're supposed to become gods after years of evolution. You can go through centuries of evolution and still make zero forward progress. >
  
  Speak for yourself. In my sleep I have:
  
  Physically punched the air on multiple occasions, waking up my wife, barely missing her.
  Physically kicked the air on multiple occasions, waking up my wife, hitting her in the shin once.
  Yelled “FUCK YOU!” extremely loud, waking up my wife.
  Gotten out of bed, walked into another bedroom, woken up my dad, told him the toilet was broken, went into his bathroom, pooped, and left it there.
  
  If some shit’s going down (literally), I’ll stay asleep, but I’ll wake you up. >
  
  I bit my bf in my sleep, just woke up to him yelling. Does that count as sleep defence? >
  
  Depends on what he was doing to you in your dream at the time. >
  
  I was fighting a woman and woke up with my mouth clamped to his shoulder. Very weird experience >
  
  Who won? >
  
  Who's next?
  You decide!
  Epic Dream Battles of History! >
  
  My defensive mechanism whilst I sleep is a lock on my front door. >
  
  So, fun fact: Different people naturally have different circadian rythms. Some people are better suited to being morning people, others function better when staying up until 4-5 in the morning and waking up mid afternoon.
  In other words, human communities have physiologically adapted to leaving some people up at night (presumably to keep watch and wake everybody else up if a tiger is stalking the camp (though now that we don't have to worry about Saber Tooth cats anymore, most of those night people are now working bar and Taco Bell night shifts). >
  
  I wake up every morning to the tic-tac sound of my dog's claws because if I don't, she will do her business inside. So I'd say our hearing is a pretty decent defense mechanism. >
  
  I remembe listening to a Mr. Ballen podcast about a girl who was camping and wolk up midway through a fox eating the top of her head. I think there was a similar one about a polar bear too. Depending on the stage of sleep we are in we can be pretty unaware of the world around us. >
  
  You raise a good point about sleep stages but then last night? My dog woke me a little after midnight (only 3 hours into sleep!) and she really had to go so, perhaps there's an override for some of us caused by specific sounds and/or known dangers. The most common of these would be a baby crying, I would guess.  Any parents out there who can concur? >
  
  How is it even possible to reply to so many answers that get you so consistently downvoted? Like, at some point reassess bro >
  
  If I had to guess, I’d say OP is downvote farming.  Either that or extremely stupid, but I’m honestly leaning toward downvote farming.  One likes to think this level of stupid isn’t possible. >
  
  Some people are also so insecure that they are completely unable to say “oh, I guess I was wrong!” Without damaging their ego.
  Case and point: OP >
  
  Hey! The phrase is actually 'case in point'. Because it means "In this point (argument/example) you can see my case at work." >
  
  Oh, I guess I was wrong! 
  Thanks! >
  
  Admitting you made a small mistake and updating your knowledge? How dare you. >
  
  there's also an evolutionary mix of night- and day-active people. some stay up late naturally and some wake up early naturally >
  
  We have defensive mechanisms, some more than others. Even while sleeping, even little but unusual sounds can wake you up. When suddenly waking up people breathe in violently, boosting the amount of oxygen in the blood, raising the heart rate. The Eyes, which are closed during sleep, can see better even without light in the dark. This trick was used by Pirates and on other Ships. The Eyepatch wasn't cause of a lost Eye, when they needed to go suddenly inside the ship, where only little light source where possible, they changed the Eyepatch and used the Eye which was under it to see better. Higher heart rate means a higher production of Adrenaline which allows faster reaction from Muscles. Also, when panicking, more blood get pumped into the extremities, the legs to assure fleeing. All these defensive mechanisms are from a time we needed them like 200.000 years ago, we use them now instinctively. These mechanics are good enough to survive, so we didn't need to develop new or different once. An animal which reached it's peak of evolution don't need to evolve until the surroundings change and make it more difficult to survive. >
  
  Other than the intelligence to build shelters and form social groups and societies where some can keep watch and protect the group while most sleep >
  
  That is because we grew smarter. Most animals do not sleep as deeply as humans due to having to be on their guard against predators. Humans who learned how to communicate effectively who learned how to create weapons and shelters can now sleep more deeply. >
  
  We evolved to be social creatures, which is the defence. By living in groups/packs with watchers we didn't need to evolve any further innate defences. >
  
  People have touched on a lot of great points but one I think deserves mentioning is that humans when asleep aren’t really in as much danger as you’d think. 
  Firstly, there’s not much in the environment that actually poses a threat to humans from a predation standpoint. Yes lions exist and have been known to hunt us but think about the circumstances surrounding when most humans would have gone to sleep. They would likely be back at camp which was probably either a cave or some other defensible place, we would be surrounded by other humans who likely would come to our mutual defense, and also humans for quite a bit of that 200k years had access to fire which would hurt in top of the arrows and javelins. It makes much more sense for a predator to wait for a human to leave that place either alone or in a much smaller group to go pick berries or whatever and snatch them then. 
  Secondly the threat from other humans throughout most of those 200k years was probably not as significant as you’d expect. There wasn’t that many of us and we were spread out across Afro-Eurasia, running into another group was probably less walking dead and more oh thank god someone I’m not related to.
  Humans wherever they have been for the last 200k years have either been one of or the apex predators of that landscape and while yes we sleep 1/3 of our lives away other predators do that too and you don’t see any of us sneaking up on a them any time soon. >
  
  Simple. You can't sleep when enemies are nearby. So if you fall asleep that means it's safe. >
  
  I understood this reference. >
  
  200,000 years of evolution is like trying to boil water in 3 seconds. Evo is really really, and I mean reaaaaaaally slow >
  
  OP you sound like your learning about the world and your curiosity is commendable, but I don’t think you understand how evolution works >
  
  I’m quite sure that if there were things that wanted to eat you prowling around where you sleep, you would be woken up by sounds in the night more often than you would if there weren’t any things that wanted to eat you around. >
  
  My girls got spayed recently, all of a sudden i was shooting awake at 4 am because on of them removed their cone, and my instincts just woke me up. Another time in the past, i went to sleep, suddenly i was standing by my fridge that i couldn't see from my bed. I hadn't shut the door properly earlier so it was open, i just done food shopping so it all woulda gone bad. So that's twice now my body has awoken me when something's wrong haha >
  
  Houses. We built houses. That’s about the most comprehensive defense mechanism possible. We even have automated motion alerts, artificial lighting, sirens, cameras, and (possibly illegally) traps. No other animal has nearly as well-guarded of a sleeping spot. >
  
  So my raging insomnia is an evolutionary defence mechanism then? >
  
  Yes, you would have been the night watchman. For animals that live in groups it's useful survival-wise to have some of them not feel like sleeping when the others do. >
  
  It’s believed that snoring is actually a sleep defense mechanism. The sound of it coming from a cave would suggest that a large creature lives inside >
  
  we learned to build homes and live indoors.  We are a lot less vulnerable than we were 200,000 years ago, actually. >
  
  We have built houses and communities and laws al for this.
  ​
  Not only that the intinct of waking up to a strange sound close to you is very real. >
  
  I disagree. Humans developed cooperation to keep watch while others sleep, fire to ward off predators, and dogs to help alert to danger. >
  
  Does OP know that humans were not the first species to sleep? >
  
  The two security doors and the concrete walls which I'm currently behind of would like to disagree. >
  
  The same can be said for many species but humans specifically have evolved a brain capable of great subconscious foresight. Obviously there will always be occasions where people think they are safe asleep and get hurt and or killed but we have a population of eight billion encounting for a reason.
  Most people do millions of calculations subconsciously and obviously deem it safe to sleep at a particular time in a particular place. The brain is really fascinating. >
  
  Try to sneak up on me while I sleep. You will have to bypass multiple locked doors and booby traps after that. >
  
  
  Craft shelter/burrow
  Pack tactics such as rotating sleep schedules 
  Insomnia
  Buddy system >
  
  Because we evolved to live in groups and at some point starting keeping dogs around as an alarm. >
  
  Ok but all animals are like that. Everything that has a brain, sleeps vulnerably.  So that's more like 500 million years of evolution >
  
  Maybe I’m just sleep deprived, but this makes total sense, my insomnia isn’t a problem its proof I’m more advanced than the rest of humanity. >
  
  "200,000 years of evolution"
  This isn't a whole lot of time for any significant amount of evolution to take place. It took like 5 million to get sweating down. >
  
  It also doesn't really describe evolution right, since life has been evolving since it began. It's not like humans started doing it just in the last 200,000 years. >
  
  As animals, our defense mechanism was to sleep in packs and maybe have someone guarding.
  Nowadays we got more complex mechanisms. >
  
  we do have a defense mechanism, it’s called other people. But since society forces all those people stay awake at night to be asleep as the same time as the rest of us, we got rid of that mechanism ourselves >
  
  If only we had some sort of structures to keep us safe and other people to form “communities” of some sort… >
  
  Humanity actually did evolve a defense mechanism for this: the night owl.
  Approximately one-third of the human population has a circadian rhythm that does not match the rest of the human race, and across them all, cover all hours of the night. This is why night shifts exist, now that we have electricity to light them.
  I am one such person. I work best if I go to sleep at 2 AM and wake at 10 AM, and I feel most awake at 4 to 8 PM, then get another burst of energy at 11 PM. In a tribe, I'd be the first of two or three night shift guards.
  Sadly, my job likes everyone on the same schedule, so I'm forced to wake up at 4 AM. My brain doesn't like that, though, so I still often only get to sleep between 10 and midnight, despite how tired I may be. >
  
  1) most animals don’t. Unless they already have passive protection systems(porcupine came to mind)
  2) we evolved past the general need for it long ago. Probably around the time we figured out how to lock doors. >
  
  I'm pretty sure that before we had locks the defense mechanism was communal living. A few people probably stayed up and kept watch. Then they passed down their genes all the way to me, and thanks to them I hate getting up early in the morning or going to bed early at night. But hey, your ancestors are welcome for their survival LOL. >
  
  Humans did evolve a defense mechanism, it’s called society. I can sleep safely because I live a house with a lock on the door, and other humans stay awake during the night to patrol the streets and watch out for potential threats. 
  The best defense was the friends we made along the way. >
  
  The “defense mechanism” is having a social group that can watch out for you while you sleep.
  Humans sleep deeper than most other animals, and don’t need to sleep as long. >
  
  Babies actually have pretty advanced and complicated defense mechanisms known as “parents” >
  
  This is not true at all. We’ve created, buildings, cities, communities, doors, doors with locks, ring cameras, and a police state that quite effectively discourages and prevents situations requiring humans to evolve sleep awareness.
  We evolved in communities of 100-150ish members, when one group or person is sleeping, other community members stay awake to protect the sleeping.
  We could also get into domestication of dogs and other animals.
  We could also talk about the way humans jolt out of a dead sleep into a survival / high alert state. 
  /showerthoughts is full of ideas that seem interesting but just are not true in anyways. OP post has 2400 upvotes…does anybody out there have critical thinking skills? Fuck. >
  
  family/tribes... which is why some of us are night owls, to protect the others while asleep. That means the nine to fivers failed/died off long ago.. in their sleep >
  
  that's why it's so hard to sleep when you're not at home. that's your defensive mechanism. >
  
  I think the house I wake up in every morning is a pretty good defense mechanism. >
  
  We've literally spent thousands of years building complex societal rules and bodies so that we can have a secure place to sleep at night. >
  
  Dogs. They evolved alongside us. And as part of their domestication they often became protectors. >
  
  I’ll have you know I’ve developed insomnia just for the occasion. Take that nighttime attackers! >
  
  Sleeping didn’t start in humans. Sleeping has been around much longer.
  If while sleeping does have its disadvantages, if it was less efficient than staying awake 24/7, it would have died off millions of years ago. But it is still here and found in pretty much all land animals. 
  Sleeping has proven to be “worth it”. Conserving energy is worth the disadvantages because of the benefits that come with it. 
  Also, as others have pointed out, there are defense mechanisms against being hunted in our sleep, such as sleeping in groups, and having some members stay awake at night. >
  
  Humans used to sleep in caves. We evolved to use huts, then houses with locked doors. A lot of people can't sleep without the comfort of a blanket no matter how hot it is because it makes them feel safe. Our defensive mechanisms are our brains and ability to shape our environment. >
  
  What about hiring body guards?  Or building a safe capsule to sleep in? >
  
  Our defensive mechanism is being a social animal, living in groups and being smart enough to make houses with man-made security >
  
  Worse example is the carbon monoxide inhalation during sleep. No immune system response at all. >
  
  These thoughts get more stupid every day. Maybe we’re devolving. >
  
  Well Idiocracy was a movie about human evolution. Just because humans as a whole are moving towards something individuals don’t see as advantageous doesn’t mean we’re not changing. >
  
  Evolution: that’s not how this works. That’s not how any of this works. >
  
  We've probably evolved to not have to worry about it anymore. >
  
  its remarkable that most species, even huge dangerous ones will leave us alone if we show no fear
  some animals are crazy and will try to eat us >
  
  I have a cat, I can relate >
  
  So stupid....our hair actually has receptors that warn us while sleeping...it's one of the reasons for restless nights sleep >
  
  We didn’t need to evolve to be not vulnerable during sleep because we had a way to work around that. If it was a big problem then yeah natural selection would have done something about it >
  
  I heard that snoring might accidentally be helpful for the purposes of scaring away potential animals because they think you are growling. >
  
  God, I wish I had failed this evolutionary stage. I will wake up at the slightest of sounds, no matter how deeply asleep I am. >
  
  The study has been done. When sleeping in an unfamiliar spot the brain does not shutdown all the way. It stays alert while you sleep. >
  
  Locks, burglar alarms, all sorts of weapons, trip wires, sleeping in shifts... >
  
  Social bonding and groups.
  I don’t think a sabertooth tiger is going to eat a tribe of 40 people without getting killed first. >
  
  Tell that to the 4 guns loaded and ready to go off once someone trips the wire.. >
  
  If true, this would suggest that IT DOESN'T MATTER. If it were a significant disadvantage, it wouldn't be that way, because we would have died out long ago. >
  
  If you work on-call, you very quickly develop the ability to wake up to sounds that aren’t normal in the night >
  
  The evolutionary defense is houses. Humans have have shells or spines so we make our own and burn down anything that threatens us. >
  
  Work smarter not harder. That's why we don't live in caves anymore. >
  
  We have evolved to snore to ward off animals.
  We have also evolved so that younger and older people sleep/are awake at different times of the night, presumably to keep watch more effectively
  Add to that us making lots of noise with singing and generally being loud apes.
  We're not totally defenseless >
  
  They already have a defence system. Its called locking your door before going to bed. >
  
  You don't set your home lasers, dogs, barbed wire, and ultra death robot before bed? >
  
  We still have the drop reflex at the point of falling asleep from when out ancestors lived in trees.  
  We have also domesticated animals with keen senses to alert us to danger.  Not just dogs, but several species of bird will sound an alarm too. 
  There is a theory than modern human senses have dulled after the domestication of the dog, as keen senses were no long as vital to survival once we outsourced them. >
  
  And so do literaly all other animals. The only exception being hedgehogs. Who can curl up into a literal ball of death. >
  
  We do have a defense mechanism, as social animals we thrive in a group, so we evolved to have different sleep cycles so there's always someone who can alert the rest of the group
  Keep in mind evolution isn't a conscious effort of the body, imagine throwing stuff at the wall and seeing what sticks, most of the time the simplest solution is the one that stays because it's the first that happens >
  
  Lol, you really can't naturally select for being eaten in your sleep, unfortunately the artist subset of humans that are less likely to get eaten in their sleep >
  
  I'm pretty confident that being inside a building with walls and a roof counts as defense. >
  
  We night owls are the defense mechanism.. currently punished by society with early rise. >
  
  Eh, 200,000 years compared to billions for how long life has been here, its not massively long tbh. >
  
  sharks 300 million, thats older then trees >
  
  Our defense mechanism is our brains. I'd say they've done pretty well for those most part. Clear individual exceptions apply >
  
  I don’t think this can be 100 percent true. Because of work, my body automatically wakes up the time I usually have my alarms on my days off. Meaning my body subconsciously sets a wake up schedule to my needs when I don’t technically need it.
  But I am still defenseless as fuck while sleeping >
  
  We dont need it anymore. And yes we actually do. We can get so stressed, after months and years of not listening to that stress, our brain will go in to a fight or flight mode. If/when this happens, we will not be able to fall in to deep sleep, and every faint sound or movement will wake us up in an adrenaline rush. >
  
  If you've ever been woken up by a sound in your house  you know this is wrong. >
  
  When we are sleeping,  for the most part,  we are woken by things that are extremely loud or extremely quiet.  
  We mostly don’t register mid range noises when sleeping.  That’s a function of evolution. >
  
  Lmao at OP just completely shitting all over any response that challenge their brain-dead take, this comment section is keeping me awake on rotation >
  
  I think I'm more protected while I sleep than during the day.
  Alarm monitoring every window and every door each second of the night, motion-activated cameras on both doors that go off before someone would even be at a point of entry and several boom sticks next to the bed. 
  Top it off with the best guard dog that signals to us every branch or wind gust that could be a potential threat at all hours of the night. >
  
  Any sort of defence mechanism?
  How about waking up to a noise, smell or touch, insomnia with adrenaline, night time sleeping, staying in groups, setting traps, ability to stay awake for>24 hours, rem sleep patterns when lacking sleep... >
  
  Many people have a reflex to wake up and punch or kick when they’re startled. It may not be a super defensive mechanism but it’s something >
  
  tribalism.
  It's literally the first thing we learn: how to ask for help. While the others sleep one person in the tribe would stay awake an look out for danger. We even adapted, so that some people have an easier time staying up late and some would wake early.
  When I used to live in a squatted property we even used to do this, because it is a really effective defense strategy. >
  
  
  We even adapted, so that some people have an easier time staying up late and some would wake early.
  
  And now we punish the night owls and call them lazy. Oh well. >
  
  Well we are social.  Maybe you mean a lone human?
  Ever wonder why almost every single village in almost any part of the world tolerates dogs? Or why we keep dogs as pets?
  At first you think it's annoying, and sure, it definitely is.
  But then you realize they are an alarm system that is literally tens of thousands of years old.
  And it's not just dogs.  We have plenty of both low tech and high tech alarm systems!
  And we're able to adapt our circadian rhythms pretty well to keep watch when we have to. >
  
  My dutch oven says otherwise. You don't have to get ready, if you stay ready. 😏 >
  
  I have two defensive mechanisms while I sleep. 
  Dog 1 and Dog 2. >
  
  snoring scares away predators because you sound bigger than you are >
  
  Our ability to build shelters that can sustain damage from natural disasters and predators makes up for "being vulnerable." This is a dumb shower thought. >
  
  Social structures and residences are the best possible defense. No evolution needed. >
  
  Our intelligence, tool use, and social structures give massive defensive benefits. We build structures like tents, huts, and walls to keep outsiders away. We use tools like fire, clubs, spears, arrows, and guns to defend ourselves. We use family units and larger villages as protection in numbers.
  Secondly, you don't seem to understand evolution very well. Evolution doesn't lead to a super-creature able to do everything. Evolution leads to something that is good enough to survive and pass its genes on. All of the methods I listed above are enough to allow humans to survive and reproduce. That's it. >
  
  I mean we aren’t subject to the same conditions that animals are that led to them to develop those defense mechanisms. Actually, seeing as how most of us live out lives now and in the future, there wouldn’t be a reason for us to evolve in any ways that would be better defensively. >
  
  To quote planet of the apes, because it's the exact reason: "apes together, strong"
  We looked out for eachother >
  
  Except for all of the other people we live in groups with that have varying sleep schedules >
  
  Light sleeping, being afraid of the dark, fire, the ability to build shelter and innovate on top of that. Homes, doors, community, police, etc.
  These things stop evolution in its tracks because it’s no longer needed. The human mind is the most powerful tool of evolution. We don’t need what other animals have because we find ways to work around the issues with our mind.
  That, and also, every species needs a downfall. There has to be a weak spot or it throws off the balance. For instance, the Industrial Revolution and and advancements of modern medicine have increased the human population to the point of largely overtopping the scales. Now, the biggest threats to the world all stem back to the fact that there are too many living human beings on the planet.
  This gives way to interesting thought about war and violence being a characteristic of humans that is needed , but I’ll stop there. >
  
  Go sleep outside and work on evolving this strength then.
  It will probably be in vain though because nobody will ever procreate with you. >
  
  Apparently if you sleep somewhere different than usual. A hotel bed for example. Your brain will not fully switch off and you won't get a proper night's rest. You remain alert to dangers all night. >
  
  I dunno, I wake the fuck up the second my cat climbs the curtains. >
  
  Nah I have spikes that come out of my skin when I sleep. Is that not normal? >
  
  Got a better one : uncanny valley effect
  People  get wierded out by things that that look " mostly  human "  but isn't. It creates  an instinctual fear response.  
  .  So, as humans  evolved...there was something out there that looked...sorta human...But wasn't...that we needed to be afraid  of >
  
  Wife: “why do you keep sleeping with that hand gun next to you?”
  Me : points at and taps the print out of this Reddit question >
  
  you will shoot yourself most likely >
  
  We aren't vulnerable. The defense mechanism that we have evolved is that we live in groups. While some humans sleep the others are awake. >
  
  We did. We built homes, made walls and slept in rotations. 
  Ape together strong. >
  
  Ever heard of insomniacs before? We’re the defensive mechanism. >
  
  I once accidentally kicked my girlfriend in the butt while sleeping because I was dreaming about a video game, so.. there's that. >
  
  I'd say my brick walls and locked front door are pretty effective defence mechanisms. >
  
  The sense of smell isn't processed in the same part of the brain as the other senses. As many animals heavily use their nose to detect things, this was our tactic way, way back. However during our evolution we relied less and less on smell, and at that point we didn't need a new mechanism to keep us safe in our sleep similar to how we don't have claws because we used pointy sticks. Living together and using the environment to our adventage is our sleep safety measure now. >
  
  I mean, so are almost all other animals. It's clear that to a large extent it's a physical/chemical/biological rule that all sophisticated brains need time to repair/rest or else quickly deteriorate in their ability to function properly. Better to have a fully functional brain 2/3 of the time than only compromised brain or nervous system all the time. >
  
  We literally build concrete bunkers around ourselves to sleep in.
  Wdym no defense mechanisms.
  Behaviour also counts, not just claws. >
  
  I me a my ex-girlfriend was able so subconsciously head punch me if I hogged too much of the duvet whilst she was asleep. That was a pretty good defense mechanism NGL. >
  
  We use group tactics and intelligence, build a shelter that others can't enter or have friends watch your back. >
  
  having huge balls works wonders
  I have seen 3 African natives walk with spears towards a kill surrounded by lions
  the pride ran away >
  
  Hah you haven’t met my son. If you wake him suddenly he comes up swinging. He flattened a teacher when he was away at a school camp. Luckily the man had a sense of humour. >
  
  This is interesting but I don't think it's completely true. We have homes and social structures in place to protect us in our sleep. >
  
  Um yes we do, we live in groups in which some individuals can watch over the others at night. >
  
  Not nearly as vulnerable as "Rocky" from Project Hail Mary. Those crab things have to have others watch them sleep. >
  
  ALL of this (big wild gestures) are our defense mechanisms >
  
  The defence mechanism is how we work in groups. Now we build a fortress/homes >
  
  it's very possible we had one back in the times where we loved wild and free, but after developing shelter it probably dissipated out over time as the need for it decreased. >
  
  Tell that to my aunt, who if even jostled slightly from sleep would fly out of bed like the Red Bull from the Last Unicorn and start punching and beating without mercy. >
  
  Counterpoint:
  If we are so vulnerable at night, how are we the dominant species on the planet?
  That should spark your intuition that something about your thought is incorrect.
  And indeed, the answer is that we (along with many other animals to various degrees) evolved Communities to deal with this problem.
  A single human sleeping alone in the wilderness is moderately vulnerable. Certainly, a sneaky predator could probably find them and bite them before they could do much of anything.
  However, a sneaky predator who tries the same thing with a group of 30 sleeping humans is going to be dinner the next day for 29 or so humans. The predators who survive are the predators who don't attack groups of sleeping humans.
  Communities are the evolutionary solution to a great many problems, and it happened millions of years ago, not in the last 200,000. >
  
  Yet another shower thought we could have avoid if people understood evolution better. >
  
  We tamed dogs to take that roll. If you remove the pressure to evolve with technology, a species has no evolutionary impetus to change because the humans with better adoptions to deal with that pressure no longer have an advantage when passing on their genes. 
  Personally, I very rarely enter REM sleep, and wake up many times throughout the night. I once had a cow that was having some health issues, and would roll over on her side when laying down and not be able to sit back up on her own. She would make little grunts of distress, but on their side cows don't have the lung capacity to make much noise. I would wake up pretty quickly if she was in trouble even if she was acers away from the house. My mother and her mother also had a knack for being able to wake up at the drop of a pin. The adaptation is here, it's just not the norm in most populations because it doesn't serve as a strong benefit to passing on the genes for it. >
  
  I feel like I missed out on the sleep part. Like even the slightest sound and I’m awake… >
  
  You're thinking of evolution in terms of a bunch of engineers designing a machine. Sure, humans are defenceless when asleep and it would be dumb not to design a defence mechanism, but that's not how it works in nature. It doesn't matter how illogical the 'design' is, the important thing is that it hasn't stopped our species from reproducing. That's literally it. >
  
  I tend to wake up if people make noise near me. Idk about yall >
  
  Fun fact: some scientists believe that snoring was a caveman's form of protection while sleeping. Apparently if "caveman snore loud in cave, snore sound like growling monster" or something. May not be true, but it's still funny to think about >
  
  What are you high? We build literal defensive structures to keep us safe as we sleep, and we utilize our ability to work together and socialize to also keep eachother safe as we sleep. We most definitely have many defense mechanisms for sleeping. This post makes no sense. >
  
  It's called being a light sleeper. And yes, we have stopped selectively breeding for it. >
  
  My pitch black room with my  black German shepherd blended into the dark. I'd say I got a defense mechanism. Also my squeaky door or windows will wake me >
  
  I have one. Night terrors. I wake up running away from my bed as fast as possible. I thought I was mentally I’ll maybe I’m just evolved >
  
  Houses... With locks... We literally built houses for this exact reason. They protect us from outside elements. If you invite the outside elements inside that's on you. >
  
  So my house with security cameras, motion detection, gun, alarms with auto phone call to security and police is not a defense mechanism? >
  
  I've seen some dumb showerthoughts, but this one is way up there.
  Firstly, humans have a longer evolutionary history than 200k years, our current form has been around that long, the things we evolved from go back millions of years.
  Secondly, that's not how evolution works, I know its easier to think and word it that way, but we don't evolve traits 'to do' something. Mutation is random, and sometimes that mutation helps you survive long enough to or makes it more likely you will procreate and pass your mutation along.
  Thirdly, the most effective defense mechanism, is a big brain, which enabled us to build shelters, weapons, and out-think predators, making some other weird defense mechanism unnecessary. We're also social creatures, so we band together for security. >
  
  What are you talking about. We have houses. 
  Before that, we had dogs. They sense the danger before we do, and they wake everyone up. Which leads to our next defense mechanism: strength in numbers. We live in community. Now there’s a whole group of people wide awake and holding their angry dogs back and discussing who’s going to spear the lion. And they will. Poor lion doesn’t stand a ghost of a chance against that. 
  It takes a stupid stupid predator to attack a human village. 
  It’s not that we don’t have defenses. It’s just that you don’t notice our defenses, because you walk right through them unhindered. Unless the dogs don’t know you, in which case you’ve got some ‘splainin to do. >
  
  You ever falling sleep and get that sudden jolt that wakes you up? That's from when we lived in trees and had a built in survival mechanism to stop us falling out as we slept. It's still there because evolution always has to take the long way round >
  
  Those two times I punched my husband while sleeping beg to differ... >
  
  We literally evolved to build things around us to keep us safe at night. >
  
  What about the heart stopping jolt we do when we’re just about to fall asleep and suddenly dream of falling off a cliff >
  
  Not necessarily, we've developed this thing (i forgot the name) that let you feel when you're being stare at by someone or something (predators) giving us a higher chance to survive and that's why you wake up in middle of the night when you feel you being watch >
  
  There is probably not a single animal that is not completely defensive if they slept outside in the open alone and without a sleep guardian member of the group.  Everything from dolphins to termites. >
  
  We evolved intelligence which has enabled us to build a 99.99% safe haven during sleep. >
  
  Oh look, another shower thought that is just a simpleton displaying their ignorance. Awesome. >
  
  I have a tripwire set up by the door attached to a 70,000 kiloton thermonuclear bomb. >
  
  Our dogs will wake the house if a squirrel so much as farts in the front yard. We’re good. >
  
  Shit I have a new born, I can hear a cricket fart these days >
  
  I dunno.. my warm and secure home, along with my beloved k9 companion seem to do the trick. >
  
  Building a secure shelter from other people animals and the elements leaves us pretty secure. And if the shelter fails me the alarm system wakes me up in time to get my best defence mechanism, my gun. I would say I’m not too vulnerable even in my slumber >
  
  Other people. Our fellow humans are our defence mechanism for when we sleep. >
  
  Have you ever woken up a veteran who’s been through hell? I promise there’s a survival reaction built-in. >
  
  But so are Most animals. Vulnerable as we are, thats why some dig in the ground or builds nest - Like we build homes and security systems. >
  
  There is that startle reflex where you punch whatever wakes you >
  
  Tell that to my brother after I punched him in the throat after waking me up >
  
  I mean at least we have big brain and thumbs to build things to protect us >
  
  A few people stand guard while the others sleep, and rotate guard duty in shifts. >
  
  You used your brain to craft a safe place to sleep, so our brain can get the entirety of a much needed sleep. >
  
  OP has never seen me hurl a 15 lb weight blanket across the room while still asleep. Pretty decent defense mechanism there >
  
  there was no environmental pressure to do so as we designed shelters thus such mutations would have no real reproductive advantage >
  
  Tell that to me when I get woken up suddenly, I'm downright mean and violent >
  
  Are you stupid, what do you think a house and doors are for? Humanity evolves with it's tools.
  Thats why we won the race >
  
  I’ve read befor that different sleep habits is what we evolved as that protection system.   Some people are night owls and can sound the alarm, while others are are mentally disturbed people that enjoy getting up at 4-5 am. >
  
  I had a guy tell me I "slept with my elbows" I guess go get some severe PTSD and you'll be a little protected from everything but yr own brain. >
  
  It’s not really the case. Humans are meant to sleep in big groups- it’s why our circadian rhythms aren’t exactly the same from person to person. I’m reading a book on it now, actually: “Why We Sleep” by Matthew Walker. It’s quite interesting, I recommend it if anyone is interested! >
  
  We have a little dog that barks at any sound in the night... So if a sound at 2am finally isn't one of the kids going to the bathroom, all those times she woke us up would be worth it. >
  
  Speak for yourself. I have three eyes and one is always open. >
  
  Maybe you don't. Talk to people who've gone through war and they can tell you someone who woke up when you got too close. >
  
  bitches walk into my room only to find that in the bed is a dummy and I'm actually behind the door with a sledgehammer