Why Are We the Only Human Species Left? What happened to others...

0:00For most of human history, we were not

0:01alone. If you could travel back 50,000

0:03years, you'd find a planet where several

0:05different kinds of humans existed at the

0:07same time. Some looked a lot like us.

0:09Others were built completely

0:10differently. Shorter, heavier, shaped by

0:12climates and landscapes that would break

0:14a modern person. One species lived on a

0:16remote island and evolved to be barely 3

0:19ft tall. Another is so mysterious that

0:21nearly everything we know about them

0:22comes from a single finger bone. And

0:25then there was us, Homo sapiens. Today,

0:27we are the only human species left. Not

0:29because we were the strongest, or the

0:31smartest, or the ones who'd been here

0:32longest. Just the ones who are still

0:34here, which raises a question that

0:36doesn't have a clean answer. What

0:37happened to everyone else? What actually

0:39happened was slower and messier. To

0:41understand how that played out, you have

0:43to start with the species that lasted

0:45the longest, which is Homo erectus. Homo

0:47erectus showed up around 2 million years

0:49ago. And to put that number in

0:51perspective, everything modern humans

0:53have ever accomplished, every city we've

0:55built, every war we fought, every

0:57language we've spoken, all of it fits

0:59inside the last few thousand years. Homo

1:02erectus was on this planet for a stretch

1:04of time so long that our entire history

1:06looks like a footnote next to theirs.

1:08Their bodies were the first to look

1:09recognizably human. They have long legs,

1:11shorter arms, a frame designed for

1:13walking and running over open ground.

1:15They were almost certainly the first

1:17human species to leave Africa and spread

1:19into other parts of the world, which

1:21means they figured out how to survive in

1:22environments they'd never evolved for.

1:24Their brains were smaller than ours, but

1:26significantly larger than anything that

1:28came before them, and they developed

1:29stone tools that barely changed over

1:31hundreds of thousands of years. That

1:33sounds like a lack of imagination, but

1:35it's actually the opposite. What they

1:36made worked so well that there was no

1:38pressure to improve on it. But by their

1:40final chapter, the world had left them

1:42behind. Their last populations ended up

1:44on the island of Java in Indonesia, cut

1:46off from the mainland, with no way to

1:48reach other groups, and no new territory

1:50to move into. The forests they'd always

1:52hunted in started shrinking. The animals

1:54they depended on became harder to find.

1:56And without enough people or enough

1:57space to recover, a species that had

1:59survived for close to 2 million years

2:01slowly ran out of options. Their last

2:03fossils date to around 110,000 years

2:06ago. After outlasting everything the

2:08planet had thrown at them, Homo erectus

2:09was gone. Let's talk about the

2:11Neanderthals, probably the most

2:12misunderstood species in human history.

2:15For decades, they were written off as

2:16dim, brutish cavemen. That image was

2:19always wrong, and the more we learn

2:20about them, the more wrong it becomes.

2:22Neanderthals were built for survival in

2:24ways that are hard to overstate. Their

2:26bodies were compact and powerful. Wide

2:28chests, thick bones, strong arms. Their

2:30faces had heavy brow ridges and large

2:33noses that warmed cold air before it

2:35reached their lungs. Their brains were

2:36on average slightly bigger than ours.

2:38They hunted large dangerous animals at

2:40close range, which is why their

2:42skeletons show injury patterns similar

2:44to modern rodeo riders. They know how to

2:46control fire, made sophisticated tools,

2:48and there's growing evidence that they

2:50buried their dead with care.

2:51Neanderthals lived across Europe and

2:53Western Asia for more than 300,000

2:55years. But around 45,000 years ago, Homo

2:58sapiens began moving into the same

3:00regions. For a few thousand years, both

3:02species lived side by side, and DNA

3:04evidence shows they even had children

3:06together. But living alongside Homo

3:08sapiens created new challenges for

3:09Neanderthals. Both species hunted many

3:12of the same animals and relied on the

3:13same land for survival. Homo sapiens

3:15lived in larger groups and had wider

3:17social networks, allowing them to share

3:19resources, knowledge, and support over

3:21greater distances. However, Neanderthals

3:23generally lived in smaller, more

3:25isolated groups, making it harder for

3:27them to share resources and recover from

3:29difficult times. At the same time, the

3:31climate kept changing. Cold periods and

3:33warmer periods constantly reshaped the

3:35environment, making survival even more

3:37difficult. Neanderthal populations

3:39became smaller and more isolated, and

3:41their DNA shows very low genetic

3:43diversity, suggesting their numbers were

3:45already declining. By around 40,000

3:47years ago, Neanderthals disappeared from

3:50the fossil record. They weren't wiped

3:51out by a single event. Instead, a

3:54combination of competition, climate

3:56change, and shrinking populations

3:58gradually pushed them toward extinction.

4:00Now, let's talk about the Denisovans.

4:02They were different from every other

4:03species on this list because we can

4:05barely see them. The entire discovery

4:07began with a single finger bone pulled

4:09from a cave in the Altai Mountains of

4:11Siberia. A fragment so small it could

4:13sit in the palm of your hand. But, when

4:15scientists extracted DNA from it, the

4:17results didn't match any known human

4:19species. Not Neanderthals, not Homo

4:21sapiens, and not anything else

4:23scientists had seen before. It was

4:25something else entirely, a previously

4:27unknown branch of the human family that

4:29had been hiding in the genetic record

4:31all along. Since that discovery, only a

4:33handful of additional remains have

4:34turned up, which include some teeth, a

4:36piece of jawbone found high on the

4:38Tibetan Plateau, and not much else. And

4:41yet, their genetic shadow is enormous.

4:43Denisovan ancestry shows up in modern

4:45populations across parts of Asia and

4:47Oceania, with some Melanesian groups

4:49carrying as much as 6% Denisovan DNA.

4:52Tibetans inherited a Denisovan gene

4:54called EPAS1, that allows them to

4:56function at extreme altitudes where most

4:57people's bodies would start to fail. A

4:59species we can barely find in the ground

5:01is still shaping how living humans

5:03survive in thin air. But, as a living

5:05population, the Denisovans faded out

5:07somewhere around 30,000 years ago. Their

5:09range may have been vast, but their

5:11numbers were likely thin, and thin

5:13populations rarely hold on when the

5:14world starts shifting underneath them.

5:17And then there's one of the strangest

5:18chapters in human history. In 2003, on

5:21the Indonesian island of Flores,

5:23researchers discovered the remains of a

5:25human species unlike anything seen

5:27before. They stood only about a meter

5:29tall and had brains roughly the size of

5:31a grapefruit. At first, many scientists

5:33were skeptical. Some argued the bones

5:35belonged to modern humans with a disease

5:37or developmental disorder. But, as more

5:39evidence was uncovered, it became clear

5:41that these remains belonged to a

5:42completely separate species, Homo

5:44floresiensis. This tiny human lived on

5:47Flores alongside Komodo dragons, giant

5:50storks, and dwarf elephants. Islands

5:52often drive evolution in unusual

5:54directions. When species are isolated

5:56for long periods, they can change

5:58dramatically. Large animals may become

6:00smaller, while small animals can grow

6:02larger. Homo floresiensis may be one of

6:04the most remarkable examples of this

6:06process in the entire human family.

6:08Their fossils date from about 100,000 to

6:1060,000 years ago, and stone tools

6:13suggest they may have survived until

6:14around 50,000 years ago. What's

6:16interesting is that modern humans were

6:18arriving in the region at roughly the

6:20same time. We don't know exactly what

6:21happened, but on a small island, a

6:23species doesn't need a massive

6:25catastrophe to disappear. Sometimes a

6:27small population facing new pressures

6:29simply runs out of time. So, why are we

6:32the only human species left? The obvious

6:34answer is intelligence, but that falls

6:36apart quickly because Neanderthals were

6:38intelligent, Denisovans adapted to

6:40extreme environments, Homo erectus

6:42outlasted us many times over, and Homo

6:45floresiensis survived conditions that

6:47would terrify a modern person. What may

6:49have actually separated us was something

6:51harder to measure, the way we built

6:52connections across distance. Homo

6:54sapiens didn't just live in groups, we

6:57built networks. Tools, techniques, and

6:59knowledge moved between communities in

7:01ways that don't seem to have happened

7:03for other species at the same speed or

7:05scale. When one group faced a crisis,

7:07the things they'd learned didn't die

7:09with them. That knowledge had already

7:11traveled. When the climate shifted, and

7:13entire regions became unlivable, our

7:15species had the flexibility to

7:16reorganize because we weren't locked

7:18into any single place or any single

7:20strategy. But even that only explains

7:23part of it. Luck, geography, and being

7:25in the right place with enough numbers

7:27at the right moment all played a part,

7:29too. We weren't destined to be the last

7:31one standing. We just happened to be.

7:33The other human species weren't early

7:35versions of us, and they weren't simply

7:36stepping stones on the way to become

7:38Homo sapiens. They were their own kinds

7:40of humans, each with a different way of

7:42surviving in the world. Homo erectus

7:44survived for nearly 2 million years and

7:47still disappeared. Neanderthals endured

7:49hundreds of thousands of years of ice

7:50age climates and still vanished. The

7:52Denisovans left behind almost no fossils

7:55at all, yet traces of their DNA still

7:57exist in people today.

7:59For most of human history, we were just

8:01one branch of a much larger family. Now,

8:04we're the only one left.