Event That Left Only 1,000 Humans Alive

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Around 800,000 to 900,000 years ago, a genetic bottleneck occurred, drastically reducing the human population. This event led to the extinction of 98.7% of the population, leaving only about 1,280 individuals. The main cause was a significant climate shift called the middle Pleistocene transition, which brought longer and harsher glacial cycles. This change made it difficult for early humans to hunt, forcing them to adapt while some animals went extinct. Scientists are still studying the exact cause and timing of this bottleneck.

Transcript

00:00Can you imagine that all modern humans came from about 1,000 people?

00:05Around 800,000 to 900,000 years ago, almost all of our ancestors disappeared,

00:11leaving about 1% of the population behind.

00:14So, what the heck happened?

00:16The Earth often goes through glacial cycles, things that we call ice ages.

00:21Back in the past, they were pretty mild and happened regularly, about every 41,000 years.

00:27The ice ages happened because of the Earth's axis.

00:30Our planet is slightly tilted at an angle, which is why its axis isn't straight up.

00:35Over thousands of years, this tilt has changed a bit.

00:38This teeny-tiny shift completely changes how much sunlight we receive,

00:42especially at the poles, and leads to incredibly strong cold or warm periods.

00:47About 2.6 million years ago, when early humans were settling in on Earth,

00:53the Pleistocene epoch started.

00:54That's the era we traditionally call the Ice Age, the one from the movies.

00:58Large ice sheets completely covered parts of North America, Europe, and Asia.

01:04It wasn't constant ice everywhere all the time.

01:07These glacial cycles came and went, and sometimes ice sheets melted for a while.

01:11But overall, things were still much snowier and colder compared to now.

01:15We can still see the evidence of this from back in the day.

01:19Those glaciers carved out valleys and left behind some awesome things like moraines and fjords.

01:24And since sea levels were super low, a huge part of the world was land.

01:29This allowed people and animals to travel between continents and spread everywhere.

01:33It was the time of the megafauna.

01:36You all know about it from the movies.

01:38Woolly mammoths, saber-toothed cats, giant ground sloths, and mastodons.

01:43Our ancestors had some fun times hunting all those giants.

01:47Now, humans didn't come from one lineage.

01:49It wasn't like monkeys slowly turned into humans.

01:51We also consisted of many species.

01:54Homo erectus, Neanderthals, and so on.

01:57But only one species, Homo sapiens, survived and turned into modern humans.

02:01Harsh conditions forced them to get smarter.

02:05They learned how to make tools, clothing, and shelters to survive.

02:08They became hunter-gatherers and invented fire,

02:11which turned out to be super useful during the Ice Age.

02:14You think?

02:15But they had no idea what horrible change was coming.

02:19Something disastrous happened about 800,000 to 900,000 years ago.

02:24Humans faced a drastic population crash.

02:27Only 1,280 people survived, give or take.

02:30Some 99% of early humans were wiped out.

02:34And this tiny 1% was lucky enough to become our ancestors.

02:38This almost extinction, unsurprisingly, was the climate's fault.

02:43It was the middle Pleistocene transition.

02:46The Earth's orbit around the Sun changed its shape a bit.

02:49Carbon levels dropped.

02:50A lot of stuff was happening, and the Earth's climate was going wild,

02:54becoming incredibly cold and dry.

02:56The sea suddenly got chillier, and Africa and Eurasia experienced horrible droughts.

03:02Looking for food was almost impossible.

03:05Scientists learned this by taking the DNA of about 300,000 people from all around the world.

03:11They used a new method to help them map the history of human evolution over a million years

03:16and learn more about it.

03:18No wonder we can barely find any fossils from that time.

03:21There was almost no one around.

03:22What's interesting is that before that happened, most apes had 24 pairs of chromosomes.

03:29But because the population became so small, two sets got fused together, and we ended up

03:34with 23 pairs.

03:36This was the final straw that separated us from other apes.

03:40Chimpanzees, gorillas, and orangutans all have 24 pairs.

03:43But our fused one became known as the human chromosome.

03:48Like a ripple effect, this little thing influenced our brain side, helped us start walking on our

03:53twos, and even form language.

03:55It took humans about 100,000 years to recover from this catastrophe.

03:59Only after all that time, they started spreading around again.

04:04Isn't that insane how we managed to go from 1,000 to 8 billion people?

04:08In any case, the Ice Age finally ended about 11,700 years ago.

04:14The warm period, called the Holocene, began.

04:17As things got warmer, human civilizations finally began to develop.

04:215,000 years ago, it was ancient Egypt, then the Indus Valley Civilization, ancient China,

04:27and others.

04:28And while we've been thriving for a while, there's one catch.

04:31The middle, Pleistocene transition changed the length and intensity of glacial cycles.

04:37Before the transition, sure, there was the Ice Age.

04:39But the cold was milder, and the glacial cycles were shorter.

04:43Things got covered in ice sheets about every 41,000 years.

04:47But after the transition, the glacial periods became longer and more severe.

04:52These cycles started following a new pattern.

04:55Although they happened every 100,000 years, they were super intense.

04:58Ice sheets grew large, even extending to the south.

05:03So from now on, ice ages, that will continue to happen in the future, will be a bit different.

05:09The next one should be at least 50,000 years from now, maybe longer.

05:13It's good for us, because it'll occur later.

05:15But at the same time, the consequences will be stronger.

05:19What our ancestors went through is called a population bottleneck.

05:23That's what we call a sudden and huge reduction in the size of a population.

05:27Usually, it happens because of things like earthquakes, floods or droughts, fires, and even human actions.

05:34Just a few people survive, and only they can pass their genes to future generations.

05:38And we've got plenty of such bottlenecks in history.

05:42Our modern species, Homo sapiens, originally lived in Africa.

05:46Around 60,000 to 80,000 years ago, a small group of them left Africa and spread across the world.

05:52It wasn't on a whim, though.

05:54They had to move somewhere because of the droughts and huge climate problems in Africa at that time.

05:59They had to go look for food and find new places to live.

06:03They traveled through the Middle East, moving into Europe and Asia, and eventually reaching Australasia and the Americas.

06:10They quickly settled across different continents and started mixing with local human-like species,

06:15like Denisovans and Neanderthals.

06:18But there was a problem.

06:19Originally, the African species were super-genetically diverse.

06:23But since only a small part of them decided to move out, they carried just a bunch of these diverse genes with them.

06:30Unfortunately, this caused a bottleneck for everyone.

06:33Human-like species from other parts of the world became less genetically diverse.

06:38Since they had a smaller gene pool, they became more vulnerable to all the harmful stuff.

06:42The African population also had a drop in genetic diversity.

06:46But at least humans managed to survive.

06:49Although eventually, non-African populations really dropped.

06:53And there were no Neanderthals or Denisovans left.

06:56Only us, Homo sapiens.

06:58That's why we can say that all modern humans came from Africa.

07:02Early humans sure had it rough.

07:04About 74,000 years ago, they went through yet another disaster.

07:09The Topa catastrophe.

07:10But keep in mind that all these things are just a hypothesis.

07:14It's not certain whether it actually happened.

07:17Now basically, scientists think that there might have been a super-volcanic eruption at Lake Toba in Sumatra, Indonesia.

07:23This volcano going crazy was an absolute catastrophe for Earth's climate in humans.

07:29The eruption was one of the most powerful volcanic events in the last 2 million years.

07:33It spewed out from 670 to 1,000 and a half cubic miles of lava in volcanic stuff.

07:41Just so you know, there are about 3,100 cubic miles of water in our planet's entire atmosphere.

07:46And this eruption had almost half as much lava.

07:50This horrendous disaster led to the formation of Lake Toba, a massive caldera lake in Sumatra.

07:56It also spewed out tons of ash and sulfur dioxide into the atmosphere.

07:59This caused the so-called volcanic winter, which means that, while it's not actually winter,

08:05the temperatures drop and the planet is freezing because all these ash clouds are blocking the sunlight from reaching the Earth.

08:12This event affected climate patterns for years to decades.

08:16This also most likely sped up the arrival of the next glacial cycle.

08:20Luckily, humans are crazy good at surviving.

08:23The global human population was reduced to a few thousand people yet again.

08:28And they still managed to overcome this.

08:33That's it for today.

08:34So hey, if you pacified your curiosity, then give the video a like and share it with your friends.

08:39Or if you want more, just click on these videos and stay on the bright side!

08:43Let's check in there for the next video!

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