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

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1. 0:00For most of human history, we were not
2. 0:01alone. If you could travel back 50,000
3. 0:03years, you'd find a planet where several
4. 0:05different kinds of humans existed at the
5. 0:07same time. Some looked a lot like us.
6. 0:09Others were built completely
7. 0:10differently. Shorter, heavier, shaped by
8. 0:12climates and landscapes that would break
9. 0:14a modern person. One species lived on a
10. 0:16remote island and evolved to be barely 3
11. 0:19ft tall. Another is so mysterious that
12. 0:21nearly everything we know about them
13. 0:22comes from a single finger bone. And
14. 0:25then there was us, Homo sapiens. Today,
15. 0:27we are the only human species left. Not
16. 0:29because we were the strongest, or the
17. 0:31smartest, or the ones who'd been here
18. 0:32longest. Just the ones who are still
19. 0:34here, which raises a question that
20. 0:36doesn't have a clean answer. What
21. 0:37happened to everyone else? What actually
22. 0:39happened was slower and messier. To
23. 0:41understand how that played out, you have
24. 0:43to start with the species that lasted
25. 0:45the longest, which is Homo erectus. Homo
26. 0:47erectus showed up around 2 million years
27. 0:49ago. And to put that number in
28. 0:51perspective, everything modern humans
29. 0:53have ever accomplished, every city we've
30. 0:55built, every war we fought, every
31. 0:57language we've spoken, all of it fits
32. 0:59inside the last few thousand years. Homo
33. 1:02erectus was on this planet for a stretch
34. 1:04of time so long that our entire history
35. 1:06looks like a footnote next to theirs.
36. 1:08Their bodies were the first to look
37. 1:09recognizably human. They have long legs,
38. 1:11shorter arms, a frame designed for
39. 1:13walking and running over open ground.
40. 1:15They were almost certainly the first
41. 1:17human species to leave Africa and spread
42. 1:19into other parts of the world, which
43. 1:21means they figured out how to survive in
44. 1:22environments they'd never evolved for.
45. 1:24Their brains were smaller than ours, but
46. 1:26significantly larger than anything that
47. 1:28came before them, and they developed
48. 1:29stone tools that barely changed over
49. 1:31hundreds of thousands of years. That
50. 1:33sounds like a lack of imagination, but
51. 1:35it's actually the opposite. What they
52. 1:36made worked so well that there was no
53. 1:38pressure to improve on it. But by their
54. 1:40final chapter, the world had left them
55. 1:42behind. Their last populations ended up
56. 1:44on the island of Java in Indonesia, cut
57. 1:46off from the mainland, with no way to
58. 1:48reach other groups, and no new territory
59. 1:50to move into. The forests they'd always
60. 1:52hunted in started shrinking. The animals
61. 1:54they depended on became harder to find.
62. 1:56And without enough people or enough
63. 1:57space to recover, a species that had
64. 1:59survived for close to 2 million years
65. 2:01slowly ran out of options. Their last
66. 2:03fossils date to around 110,000 years
67. 2:06ago. After outlasting everything the
68. 2:08planet had thrown at them, Homo erectus
69. 2:09was gone. Let's talk about the
70. 2:11Neanderthals, probably the most
71. 2:12misunderstood species in human history.
72. 2:15For decades, they were written off as
73. 2:16dim, brutish cavemen. That image was
74. 2:19always wrong, and the more we learn
75. 2:20about them, the more wrong it becomes.
76. 2:22Neanderthals were built for survival in
77. 2:24ways that are hard to overstate. Their
78. 2:26bodies were compact and powerful. Wide
79. 2:28chests, thick bones, strong arms. Their
80. 2:30faces had heavy brow ridges and large
81. 2:33noses that warmed cold air before it
82. 2:35reached their lungs. Their brains were
83. 2:36on average slightly bigger than ours.
84. 2:38They hunted large dangerous animals at
85. 2:40close range, which is why their
86. 2:42skeletons show injury patterns similar
87. 2:44to modern rodeo riders. They know how to
88. 2:46control fire, made sophisticated tools,
89. 2:48and there's growing evidence that they
90. 2:50buried their dead with care.
91. 2:51Neanderthals lived across Europe and
92. 2:53Western Asia for more than 300,000
93. 2:55years. But around 45,000 years ago, Homo
94. 2:58sapiens began moving into the same
95. 3:00regions. For a few thousand years, both
96. 3:02species lived side by side, and DNA
97. 3:04evidence shows they even had children
98. 3:06together. But living alongside Homo
99. 3:08sapiens created new challenges for
100. 3:09Neanderthals. Both species hunted many
101. 3:12of the same animals and relied on the
102. 3:13same land for survival. Homo sapiens
103. 3:15lived in larger groups and had wider
104. 3:17social networks, allowing them to share
105. 3:19resources, knowledge, and support over
106. 3:21greater distances. However, Neanderthals
107. 3:23generally lived in smaller, more
108. 3:25isolated groups, making it harder for
109. 3:27them to share resources and recover from
110. 3:29difficult times. At the same time, the
111. 3:31climate kept changing. Cold periods and
112. 3:33warmer periods constantly reshaped the
113. 3:35environment, making survival even more
114. 3:37difficult. Neanderthal populations
115. 3:39became smaller and more isolated, and
116. 3:41their DNA shows very low genetic
117. 3:43diversity, suggesting their numbers were
118. 3:45already declining. By around 40,000
119. 3:47years ago, Neanderthals disappeared from
120. 3:50the fossil record. They weren't wiped
121. 3:51out by a single event. Instead, a
122. 3:54combination of competition, climate
123. 3:56change, and shrinking populations
124. 3:58gradually pushed them toward extinction.
125. 4:00Now, let's talk about the Denisovans.
126. 4:02They were different from every other
127. 4:03species on this list because we can
128. 4:05barely see them. The entire discovery
129. 4:07began with a single finger bone pulled
130. 4:09from a cave in the Altai Mountains of
131. 4:11Siberia. A fragment so small it could
132. 4:13sit in the palm of your hand. But, when
133. 4:15scientists extracted DNA from it, the
134. 4:17results didn't match any known human
135. 4:19species. Not Neanderthals, not Homo
136. 4:21sapiens, and not anything else
137. 4:23scientists had seen before. It was
138. 4:25something else entirely, a previously
139. 4:27unknown branch of the human family that
140. 4:29had been hiding in the genetic record
141. 4:31all along. Since that discovery, only a
142. 4:33handful of additional remains have
143. 4:34turned up, which include some teeth, a
144. 4:36piece of jawbone found high on the
145. 4:38Tibetan Plateau, and not much else. And
146. 4:41yet, their genetic shadow is enormous.
147. 4:43Denisovan ancestry shows up in modern
148. 4:45populations across parts of Asia and
149. 4:47Oceania, with some Melanesian groups
150. 4:49carrying as much as 6% Denisovan DNA.
151. 4:52Tibetans inherited a Denisovan gene
152. 4:54called EPAS1, that allows them to
153. 4:56function at extreme altitudes where most
154. 4:57people's bodies would start to fail. A
155. 4:59species we can barely find in the ground
156. 5:01is still shaping how living humans
157. 5:03survive in thin air. But, as a living
158. 5:05population, the Denisovans faded out
159. 5:07somewhere around 30,000 years ago. Their
160. 5:09range may have been vast, but their
161. 5:11numbers were likely thin, and thin
162. 5:13populations rarely hold on when the
163. 5:14world starts shifting underneath them.
164. 5:17And then there's one of the strangest
165. 5:18chapters in human history. In 2003, on
166. 5:21the Indonesian island of Flores,
167. 5:23researchers discovered the remains of a
168. 5:25human species unlike anything seen
169. 5:27before. They stood only about a meter
170. 5:29tall and had brains roughly the size of
171. 5:31a grapefruit. At first, many scientists
172. 5:33were skeptical. Some argued the bones
173. 5:35belonged to modern humans with a disease
174. 5:37or developmental disorder. But, as more
175. 5:39evidence was uncovered, it became clear
176. 5:41that these remains belonged to a
177. 5:42completely separate species, Homo
178. 5:44floresiensis. This tiny human lived on
179. 5:47Flores alongside Komodo dragons, giant
180. 5:50storks, and dwarf elephants. Islands
181. 5:52often drive evolution in unusual
182. 5:54directions. When species are isolated
183. 5:56for long periods, they can change
184. 5:58dramatically. Large animals may become
185. 6:00smaller, while small animals can grow
186. 6:02larger. Homo floresiensis may be one of
187. 6:04the most remarkable examples of this
188. 6:06process in the entire human family.
189. 6:08Their fossils date from about 100,000 to
190. 6:1060,000 years ago, and stone tools
191. 6:13suggest they may have survived until
192. 6:14around 50,000 years ago. What's
193. 6:16interesting is that modern humans were
194. 6:18arriving in the region at roughly the
195. 6:20same time. We don't know exactly what
196. 6:21happened, but on a small island, a
197. 6:23species doesn't need a massive
198. 6:25catastrophe to disappear. Sometimes a
199. 6:27small population facing new pressures
200. 6:29simply runs out of time. So, why are we
201. 6:32the only human species left? The obvious
202. 6:34answer is intelligence, but that falls
203. 6:36apart quickly because Neanderthals were
204. 6:38intelligent, Denisovans adapted to
205. 6:40extreme environments, Homo erectus
206. 6:42outlasted us many times over, and Homo
207. 6:45floresiensis survived conditions that
208. 6:47would terrify a modern person. What may
209. 6:49have actually separated us was something
210. 6:51harder to measure, the way we built
211. 6:52connections across distance. Homo
212. 6:54sapiens didn't just live in groups, we
213. 6:57built networks. Tools, techniques, and
214. 6:59knowledge moved between communities in
215. 7:01ways that don't seem to have happened
216. 7:03for other species at the same speed or
217. 7:05scale. When one group faced a crisis,
218. 7:07the things they'd learned didn't die
219. 7:09with them. That knowledge had already
220. 7:11traveled. When the climate shifted, and
221. 7:13entire regions became unlivable, our
222. 7:15species had the flexibility to
223. 7:16reorganize because we weren't locked
224. 7:18into any single place or any single
225. 7:20strategy. But even that only explains
226. 7:23part of it. Luck, geography, and being
227. 7:25in the right place with enough numbers
228. 7:27at the right moment all played a part,
229. 7:29too. We weren't destined to be the last
230. 7:31one standing. We just happened to be.
231. 7:33The other human species weren't early
232. 7:35versions of us, and they weren't simply
233. 7:36stepping stones on the way to become
234. 7:38Homo sapiens. They were their own kinds
235. 7:40of humans, each with a different way of
236. 7:42surviving in the world. Homo erectus
237. 7:44survived for nearly 2 million years and
238. 7:47still disappeared. Neanderthals endured
239. 7:49hundreds of thousands of years of ice
240. 7:50age climates and still vanished. The
241. 7:52Denisovans left behind almost no fossils
242. 7:55at all, yet traces of their DNA still
243. 7:57exist in people today.
244. 7:59For most of human history, we were just
245. 8:01one branch of a much larger family. Now,
246. 8:04we're the only one left.