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00:00Humans can live almost anywhere on the planet.
00:03We're capable of adapting to the harsh conditions of the Arctic Circle,
00:07the high altitudes atop the Andes, and even in the midst of tropical jungles.
00:12In fact, few species are spread as far and wide as humankind,
00:16with us even aiming to venture to the stars and colonize alien worlds.
00:20But could evolution have taken us down a totally different path?
00:24This is Unveiled, and today we're answering the extraordinary question,
00:28what if humans were cold-blooded creatures?
00:31Do you need the big questions answered?
00:33Are you constantly curious?
00:35Then why not subscribe to Unveiled for more clips like this one?
00:38And ring the bell for more thought-provoking content!
00:41First off, what do we actually mean by warm and cold-blooded?
00:45Neither are the best nor most specific terms.
00:48Biologists would rather speak of endothermic and ectothermic creatures,
00:53referring to animals that either produce their own body heat or don't.
00:57As well as that, we have homeothermic and poikilothermic creatures,
01:01meaning an animal either maintains its own internal body temperature
01:05or it relies on its environment to regulate it.
01:08All told, as humans, we're endothermic homeotherms,
01:12because we produce our own body heat and maintain it ourselves, through our metabolism.
01:18Most other mammals and birds also do this.
01:21But cold-blooded animals, or ectothermic poikilotherms,
01:25are incapable of regulating their own temperature.
01:28That's why you see lizards in the desert bathing in the baking sunlight,
01:32because they need to warm up their bodies before their muscles and brains can work.
01:36Interestingly, though, even these aren't the only options that the natural world can throw up.
01:41Paleontologists now believe that some dinosaurs were actually mesothermic,
01:45meaning that they survived via a combination of creating and maintaining their own body heat
01:50and utilizing their environment.
01:52But for this video, let's just focus on the basic, non-dino categories.
01:57If humans had evolved to be cold-blooded instead of warm-blooded,
02:00or even if we all miraculously turned cold-blooded overnight,
02:04one of the first big changes we'd all notice is we'd be eating less food.
02:08A lot less food.
02:10Even the so-called king of reptiles, the crocodile,
02:13can actually go more than twelve months without eating anything at all.
02:17They're painted as ruthless killers of the deep,
02:19but typical crocs only average about fifty meals a year, or just one a week.
02:24If humans ate so infrequently, rather than tucking into three square meals a day plus snacks,
02:30our food bills would definitely be much cheaper.
02:33And it'd also be much easier to feed everybody around the world.
02:36And we'd only need a tiny fraction of the land we use now for agriculture.
02:40Theoretically, nobody would ever have to go hungry.
02:43Of course, you still could eat three meals a day if you wanted to,
02:47but with the much slower metabolism of a cold-blooded creature,
02:50the calories wouldn't have anywhere to go,
02:52and the added food would translate into fat.
02:55In lots of warm-blooded animals, fat is pretty important and essential,
02:59keeping mammals like seals and whales warm in freezing oceans, for example.
03:03But it could prove deadly very quickly were we cold-blooded,
03:07causing us to overheat and die.
03:09Luckily, as a cold-blooded being,
03:11you should never feel hungry enough for this to ever actually happen,
03:15but overindulgence would definitely be off the menu.
03:18Assuming that you don't eat too much, though,
03:20it'd actually be harder to get sick as a cold-blooded animal.
03:24The constant heat of an endothermic homeotherm, as we currently are,
03:28provide a perfect incubator for germs,
03:30which is why it's so easy for us to get sick from just being near other sick people.
03:35But if we were cold-blooded,
03:37our bodies wouldn't be able to cultivate these germs as easily,
03:40staving off potential infections.
03:43This is a deadly caveat, though,
03:45because our newfound cold-bloodedness wouldn't make it impossible to get sick.
03:49And if you did fall ill, the consequences could be dire.
03:52You may not spread your disease,
03:54but if you got just a little too cold,
03:57say, your heating breaks or the wind picks up when you're waiting for a bus,
04:01your lowered body temperature could damage your immune system.
04:04If an ectotherm is too cold for too long,
04:07their body could stop functioning,
04:09leaving them wholly unable to fight off disease and infection.
04:12As warm-blooded creatures, we can live anywhere with relative ease,
04:15usually by just adding or removing layers of clothing.
04:18We can even survive the likes of Antarctica with the right equipment.
04:22But if we were cold-blooded,
04:24the state of our environment becomes a matter of life or death every single day.
04:28Where most warm-blooded creatures maintain a body temperature of around 37 degrees Celsius,
04:34a cold-blooded creature is exactly the same temperature as its environment.
04:38So, if humans were suddenly cold-blooded,
04:40we'd be much better off living in jungles and deserts,
04:43along the equator and in the tropics,
04:45never straying too far north or south.
04:48If we did branch out to a colder region,
04:51we'd need to build complex habitats designed to maintain a constant, reliable 24-7 temperature.
04:57Going outside for just a couple of minutes could result in death,
05:00so human settlements would have to be high-tech places
05:03with our fundamental need for tolerable temperatures at their heart.
05:07Strangely, although travelling to places like Canada, Russia, or Scandinavia would be a lot harder,
05:13travelling into space might actually be easier if we were a species of advanced ectotherms.
05:19This is because it'd theoretically be easier to go into torpor if we were ectothermic,
05:24which is a state of total inactivity some animals can enter by slowing their metabolism to a stop.
05:30Putting humans into deep sleep is a staple sci-fi idea,
05:34but it'd be all the easier if we could just do this naturally,
05:37without the need for complex technologies that we haven't yet invented.
05:41Send some deep space astronauts on a shuttle to Mars,
05:44and if they're cold-blooded, they could nap through the whole journey,
05:48meaning they needn't take as much food and water with them,
05:51and they needn't deal with the loneliness.
05:53Though, of course, actually living on Mars would be just as tricky for any ectotherm,
05:57since the red planet's average surface temperature is minus 60 degrees Celsius.
06:02There's one final thing that's pretty important, though… brain function.
06:06The human brain uses about 20% of our current energy levels,
06:10which is 20% of our daily caloric intake.
06:13Clearly, if we only ate one meal a week, our human brains wouldn't receive the same power to reach the same levels.
06:20It's why the world isn't really run by a race of advanced lizard people.
06:24If there actually were lizard people, they'd be environmentally obliged to spend most of their days sunbathing
06:30just to get their brains and bodies to work.
06:32And they'd have to stay stuck on the equator to even begin to match the potential of a warm-blooded rival.
06:38So, even with space travel, the problems would again outweigh the plus points.
06:42Yes, we might stand more of a chance of actually getting to other planets…
06:46but would a cold-blooded crew be clever enough to work out what to do next?
06:50Probably not.
06:51With this in mind, if humans had always been cold-blooded,
06:55evolution wouldn't have happened in even remotely the same way.
06:58We certainly wouldn't be such a social species,
07:01and our hunter-gatherer instincts wouldn't have developed as they did.
07:04Instead, we'd all have sat around waiting for our next meal to arrive,
07:08expending all of our limited energy on trying to catch it in one strike,
07:13just like real-world reptiles do.
07:16It's why you see crocodiles floating ominously in the water for hours on end,
07:20biding their time for absolute efficiency.
07:24Even if we did have some intelligence,
07:26we wouldn't have needed to cooperate to do things like build, farm, and generally invent.
07:31The only time we'd ever really need to have met other people would have been for procreation.
07:36And even then, reptiles and fish aren't exactly known for their parental instincts,
07:41instead tending to leave their offspring to fend for themselves,
07:44or else ditch them before they've even hatched.
07:47And as well as all of that, we probably wouldn't even be bipedal.
07:51Instead, we'd crawl around, spreading our bodies to expose as much of our skin to the sun as possible,
07:58in order to increase our brain function.
08:00True, nobody would ever go hungry because of our extremely low metabolisms,
08:05but we also probably wouldn't care if anybody went hungry in the first place,
08:09because an ectothermic race of humans would essentially all be lazy, antisocial lizards.
08:15And that's what would happen if humans were cold-blooded creatures.
08:19What do you think? Is there anything we missed?
08:21Let us know in the comments, check out these other clips from Unveiled,
08:25and make sure you subscribe and ring the bell for our latest content.