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00:00 All of us play our own small part in the wider human story. The history of our species has
00:06 long captured the imaginations of scientists, researchers, writers, and more. So much so
00:12 that some suggest that the "truth" of our kind is far stranger than it's typically
00:16 given credit for. This video is divided into three sections. In the first, we take an in-depth
00:22 look at the already incredible story of human evolution on Earth up until this point. In
00:28 the second, we consider it alongside the history of our neighbouring planet as well, Mars.
00:33 And finally, we spread our gaze even further, to discuss theories that life may have actually
00:39 spawned in the distant reaches of the Milky Way galaxy. This is Unveiled, and today we're
00:45 answering the extraordinary question; did humans come from outer space?
00:50 Do you need the big questions answered? Are you constantly curious? Then why not subscribe
00:55 to Unveiled for more clips like this one? And ring the bell for more thought-provoking
00:59 content.
01:01 It's hard to think of human beings as primitive creatures when so many traits separate us
01:08 from the rest of the animal kingdom. We're the only species to maintain a completely
01:12 upright posture, for example, even amongst other primates. We boast a unique dexterity
01:17 with our hands, and increased brain volume and intelligence, too. It all allows us to
01:21 distinguish ourselves via the use of speech, the development of tools, the use of fire,
01:26 and so on, to grow to where we are today. Large, mass civilisations spanning every corner
01:32 of the globe. However, humankind hasn't always been quite so unique and complex. In
01:37 fact, in a time not too long ago, relative to the age of the universe, our human ancestors
01:42 had more in common with modern squirrels than with modern people. So, how did a small, rodent-like
01:47 tree climber evolve into the dominating species of today?
02:00 The story of human evolution begins with the extinction of the dinosaurs. When an asteroid
02:05 struck land 66 million years ago, as per the most commonly held theory, it may have rained
02:11 death down upon the dinosaurs, but it also allowed a new class of animals to rise out
02:16 of their shadowed holes. With most of the world's biggest creatures gone, and around
02:21 75% of Earth's total flora and fauna at the time by most counts, whole ecosystems
02:27 collapsed, and the food chain was thrown into turmoil. But, the catastrophe left massive,
02:32 empty niches and key environmental roles just waiting to be filled. And so it was the mammals
02:38 that rose to become the dominating class. And because there were so many positions to
02:43 fill, a rich and diverse evolutionary boom occurred across a relatively short period
02:48 of time. Within the next ten million years, it's thought that between three and five
02:52 thousand species of mammals emerged on planet Earth, including the earliest classes of whales,
02:58 bats, rodents, and - crucially for the human story - monkey-like primates, our earliest
03:04 ancestors. These prehistoric primates then went through many changes very quickly, with
03:10 the first significant development happening around sixty million years ago, when the evolutionary
03:14 line divided into strepsirines (also called the wet-nosed primates) and haplorines (the
03:21 dry-nosed primates). This was a key moment in the slow progression toward Homo sapiens,
03:26 as while the strepsirines remained primarily nocturnal and reliant on their sense of smell,
03:32 the diurnal haplorines developed larger brains, and were therefore able to rely on their vision,
03:37 thereby already showing two more human-like attributes. From there, the haplorines continued
03:43 to diverge for millions of years, with several of our primate cousins branching off the family
03:48 tree. However, it wasn't until about twenty million years ago that another major development
03:53 took place - the arrival of the first ape, known as Proconsul. While still quite monkey-like
03:59 in behaviour, the earliest apes began taking on physical attributes that were again increasingly
04:05 human in today's eyes. Importantly, they were significantly larger than their ancestors,
04:10 weighing up to one hundred and ten pounds, while they notably lacked a tail. Still millions
04:16 of years ago, and the apes continued their variation, branching into the great apes and
04:20 lesser apes, and gradually giving birth to some of our other evolutionary cousins, such
04:25 as gibbons, orangutans, and gorillas - all of which developed before the earliest humans
04:30 came to be. As for our closest cousins, the chimpanzees and bonobos, they arrived much
04:36 later, around seven million years ago only. But what of the human ancestral branch itself?
04:42 One of the first big steps in our transcendence from ape to human came with the evolution
04:47 of the Ardipithecus, the first genuinely bipedal genus. Despite remaining a primarily tree-climbing
04:54 species with opposable big toes, small, cutting teeth, and a brain size very similar to an
04:59 ape, the Ardipithecus developed the breakthrough ability to walk on two legs. From here, it
05:06 took massive strides through the evolutionary timetable, and within about two million years
05:10 - that's now around four million years ago - the first Australopithecus evolved. Australopithecus
05:17 retained ape-like features, including long arms and short legs, but they were becoming
05:22 significantly more human still, largely thanks to one change. The opposable big toes present
05:28 in earlier species had now moved to face forward on their feet. This meant they became more
05:34 adjusted to walking reliably, which freed their hands for the earliest known use of
05:39 stone tools. The Australopithecus thrived until around two million years ago, when evolution
05:45 evolved along two more distinct directions. While one group is said to have developed
05:49 stronger jaws to better help them eat the nuts and vegetation specifically available
05:54 at the time, another evolved with weaker jaws but with larger brains. While both branches
06:00 survived for a significant period, those with the larger brain proved to be more adaptable
06:05 in the long run. And they ultimately gave rise to the genus Homo, taken from the Latin
06:11 for "man". And here is where human history is said to truly begin. The first member of
06:16 the Homo genus was Homo habilis. Colloquially known as "handyman", the progression of
06:21 habilis is most notable for its ever-widening use of tools, which again led to many major
06:27 evolutionary advancements happening quickly. In fact, within just 500,000 years - so now
06:33 we're about 1.9 million years ago - Homo habilis had given rise to another new classification,
06:40 Homo erectus, to make possibly the most crucial evolutionary leap toward modern man. Homo
06:46 erectus was the first to closely resemble the proportions of a current human body. They
06:51 had relatively elongated legs and shorter arms compared to the size of their torso,
06:56 which was the result of their being fully adapted to living on the ground rather than
07:00 in trees. Homo erectus had a slightly larger brain size, too, although it was still only
07:06 about 60% of the size of a modern human's. And they were the first to use fire as a tool.
07:12 This, along with their bipedalism, enabled them to migrate outside of Africa, to become
07:18 the first group to be widespread across Europe, Asia, and Africa. Finally, according to fossil
07:24 evidence, Homo erectus not only gathered in social groups, but they actually cared for
07:30 their old and weak - something that was virtually unheard of until this point. It's believed
07:35 that they had empathy and were emotionally developed as well as physically - something
07:40 which allowed them to survive and even eventually thrive alongside modern humans, before going
07:46 extinct just 110,000 years ago. Over the period between 1.9 million years ago and 100,000
07:53 years ago, and as a result of Homo erectus' migratory patterns, new members of the Homo
07:58 genus began springing up all across the world map. As each new species evolved to adapt
08:03 to different environments, these various human groups began to diverge and cross over at
08:08 various historical points, causing an intricate web of evolutionary lines. This has made it
08:13 difficult to precisely know from which line after Homo erectus we modern humans find our
08:19 origins. We may have evolved directly from Homo erectus, or from one of the several species
08:24 that branched off before or after it. Nevertheless, we do know that we were neither the first
08:31 nor the last species to evolve along our branch. It's just that we're the ones that remain
08:36 today. First appearing around 300,000 years ago, Homo sapiens are and were distinguishable
08:43 from other Homo groups most significantly by their having much larger brains, an adapted
08:49 skull shape to house those larger brains, and a lighter skeletal frame. As a result,
08:55 ancient Homo sapiens go down as being an exceptionally innovative group, developing advanced tools
09:00 like fishhooks for hunting, bows, arrows, and spears also for hunting, sewing needles
09:06 for clothing, and various building materials and methods for shelter. This ensured that
09:11 sapiens would outlast all other Homo types, with the last Neanderthals, for example, dying
09:17 out about 40,000 years ago. But while that's the human story so far, evolution is far from
09:23 being done. And as much as we tend to assume that we're the ultimate, end-of-the-line
09:28 model, it will actually continue to alter us well into the future. In the past 100,000
09:33 years, for example, the average height of Homo sapiens is thought to have shrunk slightly,
09:38 although we do appear to have grown slightly taller in the past couple of centuries. Meanwhile,
09:43 although brains have been getting progressively larger throughout evolution up until this
09:47 point, ours have actually decreased in size over the past 30,000 years or so, with it
09:52 commonly said that a modern human has lost about a tennis ball's worth of brain size
09:56 compared to earlier sapiens. Luckily for us, we remain a reasonably intelligent species…
10:03 but who's to say what could happen in the future?
10:08 The prospect of life existing elsewhere in the solar system or wider universe has been
10:12 at the centre of debate for decades. Given the millions of stars and worlds out there,
10:17 is Earth really the only one actually hosting anything? And, even if it was found that life
10:22 doesn't exist on other planets right now, could it have existed somewhere else in the
10:26 past? Somewhere relatively close to home?
10:37 Although it's widely believed that Mars in its current state couldn't support complex
10:41 life, there are various theories to suggest that ancient Mars may have been a much more
10:45 hospitable, habitable environment - perhaps at one point even more so than Earth was.
10:50 It's thought that, more than three billion years ago, the Red Planet was actually similar
10:54 to what Earth is now in terms of climate and conditions, with vast lakes and warmer weather
10:59 patterns. In terms of whether it ever hosted life, NASA's Curiosity rover has provided
11:04 plenty of apparent evidence that it may have - or, at least, that it was a possibility.
11:09 Curiosity was launched in November 2011 and landed in August 2012 with the primary goal
11:15 of exploring the Gale Crater - an area that's now believed to have once been a sprawling
11:19 body of water. The rover's mission objectives were, and still are, very far-reaching, but
11:24 much of what it does, collects, studies and records, is done so that NASA scientists can
11:29 try to determine whether Mars could ever have hosted life.
11:33 First off, while navigating the Gale Crater, Curiosity discovered a host of specific molecules
11:38 and carbon chains which, according to NASA, could have contributed to the formation of
11:42 early life. Since then, during Curiosity's further exploration of the Martian landscape,
11:47 it has found evidence of sulphur, nitrogen, hydrogen, oxygen and carbon - elements that
11:52 are also essential to life. We are, after all, carbon-based beings.
11:56 The puzzle is by no means complete, and at the moment there's no solid, irrefutable
12:00 answer on whether life does, has or has never existed on Mars… but it does seem as though
12:06 early Mars at least contained all of the fundamental pieces necessary for it to happen.
12:11 John Grotzinger, the chief scientist behind the Curiosity rover, has every confidence
12:15 that Mars was once a habitable planet, even claiming that the water that once filled the
12:20 Gale Crater would've been safe to drink. It's an exciting thought, but it also ignites
12:24 another question; if life was initially on Mars instead of Earth, then how did it eventually
12:29 get here? Well, assuming for a second that life at some point did, in fact, exist on
12:34 Mars, the prospect of the two planets somehow exchanging organisms might not be all that
12:38 far-fetched given their close proximity. At the closest point in their orbits, Earth
12:43 and Mars are approximately 34 million miles apart. It is a massive distance, but not exactly
12:48 insurmountable in the grand scheme of space. And here we get to the panspermia theory,
12:53 which suggests that forms of life exist throughout the universe and travel through space mostly
12:57 on meteorites. The chances of microbes actually surviving such high-speed, interplanetary
13:03 trans-star system journeys are definitely low, but studies have shown that it is possible.
13:08 And we do already know that various meteors from other celestial bodies have made their
13:12 way to Earth, and that Mars has been pummeled with space debris in its past, as well. So,
13:17 if there's even a grain of truth in the panspermia theory, then it may well have played
13:21 out on our planet and the Red Planet. And, across billions of years, such events may
13:25 theoretically have passed vital material from Mars to Earth. Much more recently, scientists
13:30 like Stephen Benner of the Westheimer Institute of Science and Technology have added more
13:35 fuel to the theory, arguing that thanks to its store of the element boron, early Mars
13:39 may have actually been a better place than early Earth for the creation of RNA or ribonucleic
13:44 acid - an essential building block for life. So, perhaps life really did develop on Mars
13:49 first before travelling to Earth. Or, at the very least, an adequate store of boron made
13:54 it to Earth via meteorites - to kickstart evolution here.
13:57 It ties closely with the phosphate problem, which science has long been trying to figure
14:01 out. The problem posits that early Earth couldn't sustain the vital phosphates needed to create
14:06 life, but early Mars could well have done. In 2013, shortly after Benner revealed his
14:12 ideas on why Mars may have been a better breeding ground for basic life, the University of Nevada's
14:17 Christopher Adcock led a study which found that it was much more likely that phosphates
14:21 on Mars would've developed in water, compared to phosphates on Earth which weren't as
14:25 compliant with water. So, seeing as we believe life started in water, Mars is arguably a
14:30 more likely early home.
14:32 As interesting and possible as it may seem, though, the idea that life existed on Mars
14:36 is still just a theory. And the jump from the red planet perhaps hosting early microbial
14:40 life to it being the long-lost home for an ancient line of actual human beings that we
14:45 no longer know about is still a massive one. Depending on who you ask, some form of life
14:49 may have existed, or may still exist, on Mars. But walking, talking, advanced, intelligent
14:55 and recognisable humans? Not likely.
14:58 For those trying to pinpoint the origin of life, though, Mars offers an alternative to
15:02 our own planet, with some claiming that Earth increasingly seems a more unlikely source.
15:07 But there are still plenty of questions hanging over Mars in general, not least, what exactly
15:11 happened to its atmosphere? While there's still no proof that life has ever existed
15:15 or excelled there, the general consensus is that it's at least possible.
15:23 The universe is 13.8 billion years old. Modern humans have walked Earth for only the last
15:29 300,000 years of that. So, what could've happened in the long stretch of time between
15:33 the Big Bang and the emergence of Homo sapiens on this planet? There's a lot that we know,
15:39 and a lot that we don't… but some theories bridge the gap in more unusual ways than others.
15:44 A headline-making study in June 2020 claimed that there could be dozens of alien civilisations
15:59 living in our galaxy, the Milky Way. 36 was the most often-cited figure, although the
16:05 upper estimate went past 200. That's 200 individual alien societies reportedly living
16:11 on our doorstep… in cosmological terms. Now, let's be clear; there's so far zero
16:16 actual proof that there are any alien civilisations out there. The general scientific consensus
16:21 is that there must be, but we've so far found nothing by way of hard, irrefutable
16:25 evidence. The Fermi Paradox continues to plague our search for extraterrestrial life. The
16:31 2020 study, though, was inspired by various projections and predictions, including the
16:35 Drake Equation. Its claim of 36 neighbouring alien groups has since been debated and disputed.
16:42 But say there are other bands of living beings, and say they really are not so far away from
16:46 us… then what are they doing there? Some theories, most notably the Zoo Hypothesis,
16:52 argue that nearby, superior alien groups are busy watching and possibly experimenting on
16:57 us. Others, like the Dark Forest Theory, suggest that any alien society trying to survive will
17:02 wisely remain as quiet and undetectable as they possibly can. There are, though, some
17:07 more unconventional theories to suggest that if there are aliens out there, they might
17:11 not be all that different from us at all. One study, published in December 2020 by researchers
17:17 at Caltech, aimed to map the potential for life in the Milky Way more precisely than
17:21 ever before. Paying close attention to the probability that life will - and does eventually
17:26 self-annihilate - as well as the likelihood of the emergence of life, of abiogenesis,
17:31 in the first place, it delivered some interesting results. It found that life was most likely
17:36 in the Milky Way around eight billion years after it formed, and around 13,000 light years
17:41 from the galactic centre. Considering that we appeared more than 13.5 billion years after
17:46 galaxy formation, and that we're now 25,000 light years from the galactic centre, this
17:51 would suggest that humans are doing quite well for themselves. According to the study,
17:55 we're here far too late, in completely the wrong place, and are therefore way past the
18:00 peak of life in this galaxy. And yet, we're surviving. Well done, us!
18:05 But what do these conclusions infer about the rest of life in the Milky Way? One takeaway
18:09 is that, if the study rings true, there should be a band of space almost halfway between
18:13 us and the heart of the galaxy, 13,000 light years from the centre, wherein life is much
18:18 more likely to exist than anywhere else. But another is that most life in this galaxy should
18:23 have emerged more than 5.5 billion years before we did. And, if that's true, then what happened
18:29 to it?
18:30 The short answer is… it killed itself off. The Caltech study highlights the key role
18:35 self-annihilation likely plays in how far any civilisation can reasonably spread. Away
18:40 from the study, the general idea is that all life dies before it gets big enough to be
18:44 noticed. The slightly frightening assumption, then, is that the same thing will happen to
18:49 human beings; that we'll only ever get so far before we destroy ourselves from within.
18:54 But still, if even just one such civilisation did manage to survive, then they would certainly
18:59 be considered ancient to our lowly minds. Recorded human history barely goes back five-and-a-half
19:04 thousand years… but now we're imagining life that's five-and-a-half billion years
19:09 old. Not that such a hypothetical lifeform should ever automatically be billed as ancient
19:14 human… even if we could prove that it exists.
19:17 The chances of anything else separately evolving to be even slightly recognisably similar to
19:22 us are… extremely low. The aliens we see in movies and read about in books are all
19:27 too often humanoid in nature, with eyes and hands and heads and some kind of audio language…
19:33 but in reality, they'd probably look nothing like us, and according to some theories, might
19:38 not even be carbon-based.
19:40 The picture gets a little stranger, though, when ideas on panspermia get thrown into the
19:44 mix. Subscribers to various ancient alien theories argue that biological material could
19:49 have been distributed all across the universe in the time since its inception; that we think
19:54 we're rare on Earth, but that actually we're just one of countless locations that life
19:58 has reached. And this is what panspermia amounts to; the spreading of life throughout the cosmos,
20:03 usually via space dust, asteroids and colliding planets.
20:08 Directed panspermia, though, brings a degree of agency to the table; the idea now being
20:12 that life is deliberately spread to other worlds by advanced, travelling alien species.
20:17 Again, there's little by way of credible, mainstream science to suggest that this is
20:21 what actually happened here on Earth. But, with such a long time gap to fill between
20:26 the start of this planet and the start of humankind on this planet, fringe theories
20:30 abound that ancient humans either seeded here or arrived and settled here millions (or billions)
20:35 of years ago.
20:37 In this version of life, the universe and everything, it's as though we're a colony
20:40 established in the distant past by an older, more advanced version of ourselves. Through
20:45 the lens of the Caltech study, we might imagine that those older, superior humans had emerged
20:50 long ago, out of the optimum region for life in the Milky Way, 13,000 light-years away
20:55 from the galactic centre, and 12,000 light-years away from us. They then brought their human
21:00 civilisation here before carrying on their merry way into the rest of the galaxy.
21:05 But one final consideration for today's question is; what if we aren't the product
21:09 of panspermia, but we're actually the ones facilitating it?
21:13 Another popular fringe theory is that life did originate on Earth, but the history of
21:17 human evolution isn't what we generally think of it as. Instead of the earliest hominins
21:22 emerging around nine million years ago, and modern humans about 300,000 years ago, some
21:27 claim that there were humans before this… and that they became advanced enough to leave
21:31 Earth forever.
21:33 Importantly, there is, again, precious little scientific or historical evidence that this
21:38 really is the case. It's an idea, an unsubstantiated theory, but one that's captured the imagination
21:43 of many a science fiction writer before now. Again, it allows us to imagine that the Milky
21:48 Way is actually full of life, perhaps boasting far more than just the thirty-six civilisations
21:54 suggested by the June 2020 study. Only, in this version of events, many of those could
21:59 be our ancestors. It's just that they started on Earth and then set off to the stars, just
22:04 as we're trying to do today.
22:06 The biggest argument against this line of thinking, however, is that it assumes that
22:09 Earth is basically the centre of everything. That's despite the overwhelming statistical
22:14 likelihood that it isn't. If either panspermia theory is true - that we were spread by others,
22:20 or that we started on Earth and are now spreading elsewhere - it's much more likely the first
22:24 one. To bring in the Caltech study one final time, even had humans somehow instantly appeared
22:29 on this planet at the moment that Earth was born - an obvious impossibility - then they'd
22:34 still be only 4.5 billion years old. Which would still place us as arriving later than
22:39 the optimum time for life in the Milky Way, 8 billion years after it formed.
22:44 The idea becomes marginally more palatable if we imagine that humans didn't start on
22:48 Earth, but were seeded here instead by other humans. Then, theoretically, we'd have so
22:53 much more time to play with across the history of the universe. Our story could be pushed
22:58 further back, to a time before Earth and a time within Caltech's optimum parameters.
23:04 And it can be pushed further forward, because we're no longer confined to just one world.
23:09 Earth becomes just one of many that we might have visited in the past, or in the future.
23:13 And suddenly, the rest of the Milky Way is our playground.
23:17 But ultimately, all of those stipulations require us to make some gigantic leaps in
23:21 our understanding of why we're here, what it takes for us to survive, and how significant
23:26 we really are in the universe. More and more scientists are growing to accept that alien
23:31 life must exist somewhere in space… but human life? Perhaps we'll only believe that
23:36 when we see it.
23:39 So what do you think? How does the story of human evolution make you feel? Could there
23:43 really be ancient ties between us and Mars? And how likely do you believe it to be that
23:49 ultimately, we could simply be the far-flung produce of our wider, galaxy home?
23:54 For now, wondering where we came from is a fundamental, universal question. The answer
24:23 might always be shrouded in a certain level of mystery… but that's how humans may,
24:28 potentially, have come from outer space.
24:32 What do you think? Is there anything we missed? Let us know in the comments, check out these
24:36 other clips from Unveiled, and make sure you subscribe and ring the bell for our latest