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00:00 Humans, as we know them, have walked the Earth for hundreds of thousands of years, but also

00:04 for just a tiny fraction of geological time.

00:08 Nevertheless, our journey is a remarkable tale of evolution, adaptation, and survival,

00:13 with a healthy dose of extreme danger and enduring mystery thrown in for good measure.

00:19 This is Unveiled, and today we're answering the extraordinary question; what came before

00:23 humans?

00:24 Do you need the big questions answered? Are you constantly curious? Then why not subscribe

00:30 to Unveiled for more clips like this one? And ring the bell for more thought-provoking

00:34 content!

00:36 Why are we here? It's a question with both philosophical and physical considerations.

00:41 For the latter, we can also rephrase just slightly to "how are we here?" And that's

00:46 one of the most important scientific inquiries of all. So, let's take a closer look at

00:50 the incomparable story of human evolution, from our time as ancient primates to our becoming

00:55 the dominant species on this planet. And then let's go back even further, exploring what

01:00 existed before humans and what our planet was like in its earliest days.

01:04 In the vast timescale of Earth's entire history, modern humans are relative newcomers. Our

01:10 species, Homo sapiens, has existed for approximately 300,000 years… which might sound like a

01:15 long time, but it represents only a slither of Earth's 4.5 billion year life. The beings

01:21 that would eventually become humans grew up and developed with, and alongside, various

01:26 other primates at various other times. Our evolution can be linked back to a common ancestor

01:31 we share with chimpanzees and bonobos. Key moments in our particular story, however,

01:37 include the development of bipedalism, the enlargement of our brains, and the emergence

01:41 of Homo habilis, an early hominin that's thought to be a direct descendant. Next came

01:46 the mastery of fire and the development of sophisticated tools, all culminating in the

01:51 emergence of Homo sapiens proper in Africa, somewhere between 300,000 and 200,000 years

01:57 ago. It hasn't all been plain sailing. Humans have faced several near-extinction events

02:03 over the course of our couple of hundred millennia. One of the best-known examples is the Toba

02:07 supervolcanic eruption around 74,000 years ago, which researchers believe may have caused

02:13 a volcanic winter and led to a dramatic decrease in the human population at the time. It's

02:18 even thought by some that numbers may have dwindled to just a few thousand in the years

02:23 following Toba, showing just how close our species almost came to dying out. It's a

02:29 pattern that Earth has seen before, though, and again, the time of humans is extremely

02:34 short compared to everything else that preceded us. To really get a grip on things, we need

02:39 to journey back billions of years to the formation of our planet.

02:43 Around 4.5 billion years ago, the Earth formed from an ancient, swirling cloud of dust and

02:49 gas. The young Earth was a hostile place, bombarded by asteroids and comets, with a

02:54 scorching surface covered in molten rock. But, over time, the planet cooled, and the

03:00 surface began to solidify. After that, life emerged relatively quickly in geological terms.

03:06 The oldest evidence of life dates back around 3.7 billion years, meaning that something

03:12 has lived here for the vast majority of the time that Earth has existed. These early life

03:16 forms were nothing like us, though. They were simple, single-celled organisms, and they

03:21 thrived in the oceans. Earth's waters weren't laid out in the same way that they are now,

03:26 but they were still crucial; a breeding ground for the very first things to call this place

03:31 home. Over eons, life evolved and diversified, gradually giving rise to more complex forms.

03:38 Things like algae, simple multicellular organisms, and invertebrates were next in line. The first

03:44 complex animals, such as early jellyfish, appeared around 620 million years ago. And

03:50 then came the Cambrian Explosion. Around 530 million years ago, this marked a pivotal period

03:57 in Earth's history as a whole, as is witnessed by a massive and sudden proliferation of diversity.

04:03 From this point forward, life came in many, many different forms. And while the exact

04:08 mechanism that triggered the Cambrian Explosion is unknown, it ranks as arguably the most

04:13 influential stretch of time that Earth has ever seen. That said, the next chapter is

04:19 probably the most famous that Earth has written so far; the dinosaurs. Dinosaurs dominated

04:24 during the Mesozoic Era, which lasted from around 252 to 66 million years ago. However,

04:32 alongside all of the ferocious, giant lizards, there were small, unassuming, shrew-like mammals

04:39 quietly carving out their existence, as well. And these are crucial for us. Because after

04:45 the mass-extinction, probable asteroid that wiped out all the non-avian dinosaurs, those

04:50 tiny mammals rose up. They diversified like crazy, and quickly filled all the freshly

04:56 opened ecological niches. From here, and between 60 and 55 million years ago, primates entered

05:02 the fray, rapidly evolving from their mammalian ancestors. The earliest primates were small,

05:08 tree-dwelling creatures, but importantly for us, they had forward-facing eyes and complex,

05:14 grasping hands. Now is when the human begins to appear as primates over time, developed

05:20 and specialised into a variety of forms, including, eventually, homo sapiens.

05:26 And that's pretty much that. A brief timeline of the ultimate saga, life and evolution on

05:31 Earth. Except for some, there could still be more to it. And while, yes, the Cambrian

05:35 Explosion is significant, and the end of the dinosaurs is vital, there may have actually

05:40 been another pivotal point to which everything else is anchored. The arrival of alien life.

05:45 The concept of "ancient aliens" suggests that extraterrestrial beings may have played

05:50 a major role in Earth's history, potentially influencing how species evolved, including

05:55 humans. Proponents point to various apparent "mysteries" in ancient times, such as around

06:00 the construction of the pyramids and the creation of advanced civilisations like the Sumerians.

06:05 We've covered in past videos the problems that such views entail, including seemingly

06:11 entrenched prejudice and a refusal to acknowledge modern findings… but, nevertheless, the

06:17 belief in ancient aliens is increasingly mainstream.

06:20 Perhaps its popularity is tied up with some other key considerations, including the Fermi

06:25 Paradox. The question of why, given the vast number of potentially habitable planets in

06:30 the universe, we haven't yet detected any signs of advanced extraterrestrial civilisations.

06:35 Is it because we're only here because the aliens have placed us here, at a distance

06:39 from themselves? Or, indeed, are we yet to find aliens because actually we are the aliens?

06:45 We also have the theory of "directed panspermia", which argues that any advanced enough group

06:50 would purposely contaminate other worlds and star systems. To a very small degree, it's

06:55 what we may have already done via the Apollo trips to the moon and our ongoing rover missions

07:00 to our closest planets. But, also, ancient alien theories might suggest that rather than

07:05 facilitating panspermia, we're the result of it. As to how that broader framework would

07:10 fit into everything we know about evolution to this point isn't clear. What is clear

07:15 is that, however you view it, in the grand tapestry of Earth's history, humans represent

07:20 only a tiny, tiny thread. Conventional science says that before us, the planet saw the rise

07:26 and fall of countless other lifeforms, from single-celled organisms to massive dinosaurs.

07:32 Alternative speculation suggests that aliens might have had something to do with it. But,

07:36 finally, you might wonder, why does any of it really matter, anyway? We're here right

07:41 now. How we got here is besides the point. But, actually, understanding what came before

07:47 humans is not just an exercise in satisfying curiosity about the past… it has profound

07:52 implications for our present and future. By understanding our origins, we can appreciate

07:58 the interconnectedness of life on Earth today, and the complex processes that have shaped

08:03 us and everything else. Knowing how we came to be, we can better grasp the incredible

08:08 diversity that exists in our world… which is essential knowledge for conservation, but

08:13 also in maintaining the future health of humankind itself. If we can track the key moments and

08:19 adaptations that led to our emergence, then we can better trace the development of traits

08:24 such as bipedalism, brain expansion, tool use, and complex social structures. And, lastly,

08:31 we can use all of that - all of what we know about ourselves - in the continued search

08:36 for extraterrestrial life away from planet Earth.

08:40 There is little reason to suggest that alien life would look or be anything like human

08:44 life… but that's why knowing how we got here is important. Because it allows us to

08:49 backtrack and explore all of the other directions that life might have taken. In the meantime,

08:54 of course, human evolution is ongoing, and the question of what will come after humans

08:59 - or at least, after today - is very much up for debate. Where do you think we could

09:04 be headed? Because, for now, that's the story of where we came from.

09:09 What do you think? Is there anything we missed? Let us know in the comments, check out these

09:13 other clips from Unveiled, and make sure you subscribe and ring the bell for our latest

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