Skip to main content
Loading Explore guides…
Human Evolution Overview · Acedra
Home
Explore
Biology
Human Evolution Overview
Sign in to save
Chat
If YouTube asks you to sign in, open the video on YouTube.
Watch on YouTube
Reload player
Transcript
77 segments
Copy
Hide video
0:00
humans. Man, oh man, what a thing we've become. We've basically taken over the world with our technology, global societies, and most recently our internet extravaganza. But at the end of the day, we are creatures of the earth. We breathe, we sleep, we consume, our bodies are made of blood, guts, and bones. Just like every other species, we are descended from a long line of ancestors. The features that make us human evolved over millions of years and the species that came before us. Human
0:23
evolution is one of the most intensely studied aspects of Earth's history. So, obviously, we're the ones doing the studying. Where we came from and how we got this way are questions that people have been examining since we were able to examine. The story of human evolution spans several million years and involves dozens of ancient species that are our evolutionary ancestors and cousins. The clues to our evolutionary past can be found in our genes, the fossil record,
0:45
and in the biology of our living relatives. There's a lot of we haven't figured out yet, but there's also an insane amount of that we have figured out, and scientists are constantly doing more research and filling in the gaps with new discoveries. And so I decided this would be the perfect topic for the newest series on this channel. We'll take a tour through human evolution from the earliest species that were kind of humanlike all the way to modern humans, which are obviously very humanlike and
1:06
introduce you to some lost lineages along the way. Groups that went in totally different directions, others that we encountered and got confused about and on occasion a little weird with. Yeah, this gets all sorts of twisted. So let's start from the beginning. Without further ado, my name is Lindsay Nicole and this is the evolution of us that we know of. Before we get started, let me address the elephant in the room. The pink guitar-shaped elephant in the room. Very
1:30
different from my usual guitars on the wall. This is my first guitar ever, and it was signed by Alltime Low when I was 12, and I never played it again. I took the strings off because I wanted to preserve the signatures on it. I picked it up from my parents house because I wanted to take it. I thought that my first guitar would be a good guitar to have for the first episode of this series. So, that was my thinking. Let me know what you think. It's a Carly guitar. Wow.
1:56
Check it out. As you can see, I took some stickers off, but I couldn't get the mammoth one off because Alex Gasgarth put his signature over it, which is fine. As always, we're going to get the general information out of the way. This particular information is general for the entire series, just so you know. Just so we all know what the [ __ ] is going on. All life on Earth is related in a giant evolutionary family tree. More closely related species have a lot more in common, just like you and
2:18
your siblings and your cousins. Humans are primates in order. Yes, primates. Which means we belong to the same order as lemurs, lorises, tars, and monkeys. These are the species most similar and most closely related to us. Within order primates, humans are part of a taxonomic family called homminidity. Also known as the great apes. Some of our fellow living hominids are orangutans, gorillas, chimpanzees, bonobos. We all share features like grasping hands, fingernails, no tails, which kind of
2:46
sucks. Think having a tail would be cool. complex social behaviors in most of our genome. And just as a side note, gibbons are also apes, but they're classified just outside of the great apes and typically called lesser apes, which is rude, I must say. Gibbons are sick as [ __ ] They deserve a better name. Maybe the petite apes. They look like they would like to be called tiny and petite. Anyway, within the great apes, our closest relatives are chimpanzees and bonobos, which are both
3:09
classified within the genus pan. So, we're all on the same page. That means humans did not evolve from chimpanzees. No, humans and chimps are descended from the same ancestor. Our genus is homo. Homo sapiens. Homo is the genus pan. Chimps and bonobos. Homo. Us descended from a common ancestor. That common ancestor is not a human or a chimpanzeee. Just like this grandma eventually led to you as well as your cousin. Your cousin is not you and your cousin is not your grandma. So chimps
3:40
and bonobos aren't grandma. They are our evolutionary cousins. Our evolutionary grandma is that common ancestor. And obviously a lot of [ __ ] happened between grandma and you and cousin. There's other steps along the way. And that's what this whole series is. That's what it's all about. Based on the similarities in our genome, scientists estimate that the split from our common ancestor from chimps and bonobos happened sometime between 8 million and 5 million years ago during the late
4:03
measine epic. That split gave rise to two lineages. One that led to chimps and bonobos pan and one that led to us. Hell no. All the species on our side of the split are called hominins. So to recap cuz the words are disgustingly similar. Homminids are the great apes and homminins are the members of our human lineage. All the species more closely related to us than any other living apes or homminids. I don't know if you saw but I did a recent video on an early homminant ancestor and I made this
4:30
distinction and somebody in the comments had a very helpful tool to remember the difference between homminids and homminins. And it's actually been helping me a lot because I get them mixed up a lot all the time. homminids because it includes all the great apes. Donkey Kong which starts with D would also be a homminid. So homminid Donkey Kong and then homminin which ends in N Donkey Kong is not a part of. Okay, thank you for the lovely comment. I appreciate it and we'll be using it for
4:55
the rest of my life. Eventually the homminin lineage would give rise to our species Homo sapiens. But before that came earlier species like homohabilis homorerectus and before that the orolopiththesines which include the famous Ethiopian fossil named Lucy. But we're not there yet. Let's go back to that image of a tree. As you can see, this is a very different vibe than the classic image of human evolution as a straight line from chimp looking thing to standing up stretched out to human.
5:18
The one you might have seen on religious billboards on the highway trying to disprove evolution. Sure, I'll give it to him. That was the classic way to try and explain evolution a couple decades ago. But it's misleading. That's not what evolution is, and it's not what we should think of it as. Just like the family tree of all life on Earth. You can think of human evolution specifically as a zoomed-in section of that tree or its own tree entirely or a bush, whatever you want honestly, as
5:39
long as it has all sorts of branches, some that split, some that end, and even some that intertwine cuz the homminin lineage is full of aunts and uncles, third cousins, a strange great nephews once removed. The nature never gives [ __ ] to you straight. And that is true in a variety of different ways. Homo sapiens didn't develop as the end point of a straight line of evolution. We emerged as a branch from a diverse entangled mosaic of relatives. And it turns out we have a pretty fantastic
6:03
fossil record of all these hominins going back four million years or so. But the picture starts to get a bit muddy when it comes to some of the earliest members of our lineage. Before hominins evolved their distinctive features and expanded diversity, they started out as a fairly small group that were pretty similar to all the other apes of the late messene epic. This makes it tricky to identify which of those ancient apes truly represent the early stages of
6:23
homminin evolution. So to do this, paleo anthropologists look for subtle clues. slight differences that might indicate the beginnings of distinctive hominin features. One trait scientists keep an eye out for is brain size. Modern human brain tends to have a volume of around 1,400 cubic centimeters. For comparison, chimp brains are more like 300 to 400 cubic centimeters. Our brains are outrageously large. Nuts. Brain size got bigger over time in the hominin lineage.
6:47
So, a slightly bigger brain case, that's the big space inside your skull where your brain fits. It's like the suitcase for your brain, can be a potential identifier of an early hominin species. Another iconic feature of ours is bipedalism, which lets you be able to do this if you want to. This is one of the most unique and weird things about humans. We walk on two feet with our bodies held upright. Pretty much no other animals do this. It's like us and penguins. That's about it. I know you're
7:11
thinking, "What about other birds?" Cuz they also walk on two feet, but they're all like bent over. They're not upright in a straight line. Because of this unusual walking style, we have a bunch of unique adaptations in our hips, legs, spines, even in our skulls that help us support our bodies in this upright position. It's an unusual position. Finding similar features in fossil apes can be another clue to identify early hominins. And finally, we can look at
7:32
jaws and dentas teeth. Humans have flat faces, unlike the protruding jaws of other apes. And our teeth are pretty small compared to our cousins. We're also missing certain specialized features like the CP3 honing complex. Another thing I'm pissed about. Let me explain why. T stands for canine. P3 stands for third preolar. Honing refers to the fact that these teeth hone and sharpen each other. In other apes, when they open and close their jaws, the lower preolars grind against the back
7:58
edge of the upper canines. This constant grinding keeps those canines extra sharp. Zing zing. If we still had that, that would be sick. Objectively, I imagine it would lead to a lot more violence involving biting, which is not sick. Maybe biting off tails if we still had those, too. Cuz yeah, CP3 honing complex lets apes bite each other's faces off if they want to. We have to use our hands and tools to rip each other's faces off instead of our teeth, unless you live in Florida. So features
8:23
of the brain case, jaws, and teeth, and hips and legs can all be used to identify fossils of early hominins, but this is easier said than done. First off, lots of ape fossils are only partially preserved. So a lot of the times we don't get all the helpful [ __ ] in one fossil. Also, convergent evolution, that's a thing. Sometimes a feature can evolve more than once. Happens a lot, actually. Turtles and birds both have beaks. Bats and birds both have wings. Bats and whales both
8:45
echolocate. Crab form, cat form. It's totally possible that some other ancient apes could have evolved slightly bigger brain cases or smaller teeth. Actually, the self-sharpening tooth setup seems like it was lost in multiple groups of fossil apes. So, finding a fossil with just one hominin like trait isn't necessarily a guarantee that it's actually an early hominant. Convergent evolution overall, cool, fun to talk about, but in this case, can be annoying as [ __ ] cuz it makes things muddy as
9:07
[ __ ] Another thing that's hard to nail down, where our early ancestors lived. For a long time, the main idea has been that early hominins lived in grasslands or in sparsely forested habitats on occasion. Scientists suspected that our ancestors stopped climbing trees because they lived in places where there just weren't that many trees anymore. But this idea has fallen apart a bit over time. Fossils of ancient hominins are commonly found with or near the remains
9:27
of forest dwelling plants and animals. Many ancient hominins retained adaptations for climbing even as they evolve features that help them walk upright. And even today, apes like chimps and gorillas spend lots of time on the ground even though they live in dense forests. So, just like the straight line image of human evolution, the idea that early hominins left the trees behind to stroll across the savannah is also a bit too simplistic. Reality is much more twisted than that.
9:48
All this talk of muddiness and twistedness might make it sound like we don't know [ __ ] about early human evolution. But that is not the case. There are two famous fossil apes that made it out of the mess and are thought to represent the earliest stages of homminin evolution. First is Sahilanthropus Chadensis, which might just be the earliest homminin that we know of. If you're not new to the channel, you already know what the [ __ ] is going on. I got it tattooed on me a
10:07
couple months ago. Oh, [ __ ] Too short. There it is. Now, I'm going to introduce him to you in a less painful way. Sahilanthropist is mostly known from a single partial skull that was discovered in the Jurro Desert of Central Africa. This single partial skull between 2001 and 2002, a team of paleontologists discovered this skull along with some teeth and jaw fragments while excavating at a site called the Taus Manala locality in northern Chat. At the time, they had an idea of what they were
10:31
looking at, but the proof had not been yet excavated from the pudding. So they named the skull tumi a word in the local doza language that means hope of life. When the discovery was published in 2002 it was identified as an early hommin and it was also given an official scientific namethropist chenensis badass name and is essentially a translation of where the fossil was found. The species name chensis means from chat and the sahel is the name of the region of Africa just
10:54
south of the sahara which includes parts of chat. Anthropus means human or person like in the word anthropology. So sahelanthropus chetsis sahel person from Czech. Later on, scientists identified some more teeth and lower jaw material that belong to a philanthropist and possibly some limb bones that might be this species too. Possibly to this day, the original to my school is the best bit we have of this ancient ape. Right off the bat, two things were really exciting about this discovery. First,
11:19
its location. Before the 21st century, pretty much all early hominins in Africa had been found in the East African Rift Valley and South Africa. This gave rise to the east side story theory, which proposed that the African Rift Valley was where early human evolution must have taken place. The discovery of Sahalanthropus in West Central Africa was fresh bit of evidence that early hominins were more widespread than scientists had realized and that the mysteries of our oldest ancestors might
11:41
be found beyond the Rift Valley. Another exciting thing, its geological age. It appears to be about 6 to 7 million years old. Like I said before, scientists predicted based on the genetic data that the hominin and chimp lineages split between 5 and 8 million years ago. This means Sahalanthropus is right in that perfect pocket to be one of our earliest homminins. But the age of Sahalanthropus has been a bit tricky to determine. To understand why, you need to know how
12:02
paleontologists date things. That's right, [ __ ] This is dating 101. The most common technique of dating fossils is radiometric dating, which relies on measurements of radioactive elements. The short explanation is certain elements in nature break down over time at a rate that we know so we can measure it. Scientists can take a rock or a fossil with some broken down elements inside, count up how much has broken down so far, then calculate how long it takes for that amount of
12:27
breakdown to happen. That's the age of the sample. Here's the long explanation. And we're going to get into some chemistry [ __ ] It's why it's taken me so long to explain dating cuz you know I don't like chemistry [ __ ] All matter is made up of atoms. And at the core of an atom are protons and neutrons. These are particles. Protons and neutrons. The number of protons determines what element an atom is. Carbon has six. Nitrogen has seven. Uranium has 92. The number of neutrons
12:53
and protons together determine the atoms atomic weight. Carbon, for example, is usually six protons and six neutrons for an atomic weight of 12. Scientists call this carbon 12, but it also comes in other varieties. Carbon 13, carbon 14, which have extra neutrons and so are atomically heavier. These alt versions of an element are called isotopes. They have the alt hair isotopes. The isotopes of some elements are radioactive, which means they'll eventually fall apart.
13:19
That's what happens when you listen to that rock and roll music plaguing our society. It's destroying our youth. Carbon 14 is a radioactive form of carbon. Each carbon 14 atom has six protons and eight neutrons. That's an unstable combination. Unstable. Eventually, each atom will lose a piece of one of its neutrons, which changes the electric charge of the neutron and turns it into a proton. So then there's seven protons and seven neutrons. And you know what that is now? Nitrogen. 14.
13:45
Yeah, it turned gay. Friaking frogs gay. This process is called radioactive decay. You might be wondering what happens to that lost piece of neutron. Well, it gets launched out into the world. This is why some radioactive materials can be dangerous because tiny particles are shooting off like missiles can damage our precious cells. Carbon 14 is just one example of a radioactive isotope. There's tons of them. Potassium 40, rubidium 87, iodine 131, uranium 235, etc. And they all decay the same
14:11
way in a pattern of logarithmic decay that can be measured in half- lives. For example, iodine 131 has a half-life of 8 days. You have a sample of iodine 131. half of it will decay in eight days. Then half of what's left will decay in another eight days and so on. Each passing half-life, you lose half of the remaining sample. Every radioactive isotope has its own half-life, but the pattern of decay is always the same. So scientists can study a bit of radioactive decay in a lab and calculate
14:38
the full half-life. Some isotopes have half- lives of hours or minutes, but others have half- livives of thousands or millions of years. And that's where radiometric dating can be used. Potassium 40 is a radioactive isotope that naturally occurs in minerals like feldspar and mica. Over time, it decays into argon 40. Once a pile of molten lava cools into solid rock, any potassium 40 becomes locked inside. Then slowly the potassium 40 all turns into argon 40. So geologists can get a rock
15:06
sample with the right minerals, measure the amount of potassium 40 and argon 40, calculate what percentage of potassium 40 has already transformed, then figure out how long that amount of decay takes. If half the potassium 40 has decayed, it's been one half-life since the rock solidified. So, a short explanation again, elements like potassium 40 decay over time at a continuous rate. If we can measure how much decay has already happened inside of a rock, we can
15:29
calculate how long it's been decaying for. Boom. That's the age of our rock. Fossil hominins are usually found in African sites with volcanic ash deposits. Those volcanic rocks are a great place to find minerals like potassium 40. But the Taurus Manala locality where Sahalanthropus was found doesn't have the right kinds of minerals. So instead, scientists first determined the age of the site using a different technique called biochronology. Yeah. All of that was to
15:52
tell you that they couldn't even [ __ ] use the usual dating technique. Sorry, but I had to explain it for context. And also, biochronology is a lot more straightforward, so no need to fret. Different species lived at different times. If you find a T-Rex at a fossil site, you know that site is at the end of the Cretaceous period cuz that's when T-Rex was around. We have that [ __ ] dated, figured out. So, anything else at that fossil site will be at the same
16:13
time as that T-Rex. Sahilanthropus isn't the only fossil species found at the Taurus Manala locality. There's also the saber-tooth cat mcceris, the hyena relative, the ancient elephant locked and ankis, this ancient horse. Luckily, these species are also found at other fossil sites in Africa, and many of those sites have raditric dates associated with them. So by looking at the age of those other sites, scientists could figure out that the overlap of species alongside Sahalanthropus was
16:38
possible between 6 and 7 million years ago. Not only does that put Sahalanthropus in the late measine around the time we predict homminins first evolved, but it also makes Sahalanthropus the oldest homminin species that we know of. And we're not done with the dating [ __ ] yet. Later research provided extra support for this age using a different form of radiometric dating called cosmogenic nucleotide dating, which sounds like some sci-fi [ __ ] and it kind of feels
17:01
like it. It means using radioactive isotopes that are formed by cosmic rays from space. The earth is constantly being bombarded with radiation from space. This is mostly harmless to us luckily, but it can warp the shape of certain atoms, turning them into unstable isotopes. Carbon 14 is formed this way in the atmosphere and also another radioactive isotope called burillium 10. I like the word burillium. It reminds me of the word vermilion. Vermilion is a very lovely color that is
17:29
nice as an accent light in your home. Once it's formed, burillium 10 rains out of the sky and accumulates in soils. Once a layer of soil becomes buried underground, no more burillium 10 can get to it. Then, just like the radioactive potassium and lava rock, the burillium in the soil slowly decays. Just like potassium dating can determine how long ago a rock cooled and solidified, burillium dating can determine how long it's been since soil was last exposed to the sky. Pretty
17:51
sick. Researchers were able to measure burillium 10 from the tourista locality. They calculated that the sediments around Sahalanthropus were buried between 7.2 and 6.8 8 million years ago. That overlaps with the earlier estimate of 6 to 7 million years ago. Boom. Even more likely that Sahanthropus is about 7 million years old. Over time, there has been some uncertainty. Some researchers have evidence that the Tumi skull might have been moved from its original
18:12
location at some point. And if that's true, that sucks cuz then the age of the nearby fossils and sediments might not be the same as the skull itself. And yeah, that would just that would just really suck. So, we need more fossils. Pronto. But it's not just the age that makes the honipus a great specimen for studying human evolution. It also has features we might expect to see in an early homminin. In many ways, sephylanthropus is similar to other African apes. Its elongated skull, large
18:36
cheekbones, small brain case, but it also has features that are similar to later hominins. It has relatively small teeth, and it doesn't have that specialized tooth sharpening arrangement we see in other apes. The teeth are covered in an extra thick layer of enamel, thicker than most apes, but not quite as thick as later hominins. And the jaw protrudes forward a little bit less than most other apes, but not quite as flatfaced as later hominins. So, a nice combo of features that could very
18:58
well represent an ape species that had just begun evolving along the path that would eventually lead to humans. Unfortunately, with limited fossil evidence to go by, it's hard to say much for sure about how Sahilanthropus lived, like diet. Unclear based on what we know about its environment and similar ancient apes. Paleontologists think Satanthropist mostly ate plants, but its teeth and lower jaws aren't very well preserved. So, there's not a lot of direct evidence to confirm that. And one
19:20
of the biggest mysteries is how they walked. What? Sahilanthropus bipedal. Early on, researchers examining the Tumi skull noticed the strange position of the frame and magnum. That's the hole in the skull where the spinal cord passes through to connect with the brain. In most animals, that hole is located on the back end of the skull cuz they're all like that. But in humans, it's underneath the skull cuz we stand upright and our spine meets our brain from below. In Sahilanthropus, the fame
19:42
and magnum is positioned slightly more toward the underside of the skull compared to other apes. So, looking good for an upright posture. Other researchers focused on the scars around the back of the skull, signs of where neck muscles attached. But scientists have debated back and forth on whether that musculature is more quadripedal or bipeedal in nature. At this point, we need some legs, but like I said, nothing beyond the skull and jaws is known for now. There is a femur, the thigh bone
20:05
that was found alongside the tumi skull. But whether or not it actually belongs to the same ape is unclear. Even if it does, the bone is only partially preserved. And researchers have disagreed about whether it more resembles the leg of a quadripedal ape or a bipeedal hominant. Also, a couple of arm bones, a left and right ulna that might belong to Sahilanthropus. These bones have a similar anatomy to the arms of climbing apes. So it seems that Sahalanthropus or maybe a different ape
20:26
that lived nearby was a regular climber. Somebody was climbing. Just got to figure out who. If Sahanthropus was the climber, it definitely would have had things to climb. The fossils and sediments of the Tourist Manala locality show that the ancient environment featured lakes and rivers along a forest and wooded savannah home to other tree dwelling species like colibus monkeys. Overall, Sahanthropus is a very sick find. To my makes for a sick tattoo, but there's plenty of uncertainty about its
20:50
anatomy and lifestyle. Scientists don't even all agree that it's actually a hominin. Maybe it's an earlier branch of the ape family tree. Maybe it's not quite a hominin, but close to the shared ancestors of humans and chips. At one point, researchers even thought it was more closely related to gorillas. But the scientists who originally published a helanthropist stand by its identity as a hominin. And the study that compared CT scans of ape skulls found that all
21:10
the features of the tumi skull compared best with hominins. So hominin for now. It's not really surprising that there's disagreement about how to interpret this species. It's muddy as [ __ ] As always, we have limited fossil material to go on. And at this early stage of homminant evolution, many of the most identifiable features of the lineage were only just beginning to develop. And there's a lot of researchers interested in studying human evolution. So, there's a lot of
21:31
different opinions and hypotheses to consider. Luckily, Sahalanthropus isn't our only window into early hominin evolution. Turns out another promising candidate for the oldest known hominin was discovered only about a year before Sahilanthropus. In the year 2000, a team of paleontologists led by the Kenya paleontology expedition discovered fossils of another hominin in the Tugan Hills of central Kenya at four different sites among the hills. They found limbboats, teeth, and jaw fragments that
21:54
didn't match any known species. They collected a total of 13 fossils representing at least five different individual apes. In 2001, researchers used these remains to describe and name a new homminin species. Auroran tugensis. The species name Tuganensis means from Tugan, referring to the Tugan Hills where the fossils were found. And auroran is a word that means original man in the local Tugan language. So this one is original man from Tugan. It's also got a cute nickname cuz again
22:19
people love nicknaming [ __ ] Ancient human relatives especially. Auroran was also called the millennium man. It turns out this ancient ape might have actually been discovered long before it got its original name. A single fossil ape mer was found in the tugan hills way back in 1974. It's hard to know for sure but it might have also been from Auroran in 2001 when it was recognized as an early homin. Auroran was the world's oldest known member of our lineage, dating to
22:41
around 6 million years ago. This age was determined using a [ __ ] ton of methods. Back when Aurorin was alive, Jugan Hills were occasionally flooded with lava flows, which cooled into solid ignous rock layers. These lava rocks include minerals that contain radioactive potassium 40, which can be used for radiometric dating. Geologists use potassium dating on lava rock layers above and below the formation where Auroran was found, calculated an age of around 6 million years old. Then they
23:04
double checked that with biochronology. Auroran was found alongside other fossil species like ancient pigs and elephants that are commonly found at sites from the late measine around 6 million years ago. And then for good measure they also check the age using magneetto strategraphy which is a dating method based on the fact that the earth's magnetic field has a habit of flipping over from time to time. Yeah. Very occasionally the north magnetic pole moves to the south and vice versa.
23:27
Obviously the earth doesn't [ __ ] flip over just the magnetic polarity. So you wouldn't necessarily notice if it happened today, but your compass would be [ __ ] up for a second and your GPS also [ __ ] up. When lava cools into solid rock, magnetic minerals orient themselves along the Earth's magnetic field, just like the needle in your compass. The direction these minerals point depends on whether the Earth was experiencing normal or reverse polarity at the time. So by looking at lots of
23:49
geological layers, scientists have put together a timeline of magnetic flips. In this particular formation where Auroran was found, the magnetic signature of the rock shows they formed during a period of reverse polarity known to have lasted between 6 and 5.7 million years ago. So three different dating methods, radiometric dating, biochronology, and magneetto strategraphy all point to the rocks surrounding Auroran being about 6 million years old. Until Sahanthropus
24:13
was published the following year, Auroran held a record for the oldest known hominant, the first one known from the late messene epic close in time to the origins of our ancestral lineage. Since the original discovery, some more fossils of Auroran have been discovered elsewhere in the Tugan Hills. Some of these are younger, less than 5 million years old, and some have been identified as a second species, Auroran Prians. And as you would expect, Aurorin is known
24:32
from very incomplete remains. The only parts of the skull that are known are teeth and lower jaw fragments. So, we don't have a lot of information about the shape of the face or the brain case. That sucks cuz that would be nice to know, but there are arm and leg bones known from Auroran. So, we have a lot of information about how it moved. Specifically, the shape of the hips and thighs make scientists very excited. The thigh bones have a lot in common with ours. They meet the hips at a similar
24:55
angle as in modern humans. And the femur head, the part that fits into the hip socket, is a similar shape as in modern humans. All in all, the leg and hipbones of Auroran form sort of a bridge that supports the upper body, which might have allowed it to walk upright on its legs. But to what degree is still unknown, might have been only occasionally walking upright, or maybe had a totally different style of locomotion. To really know for sure if Auroran was bipedal would be great to
25:17
have some footprints. And it turns out maybe we do. On the Greek island of Cree, paleontologists have identified fossil footprints that appear to be the bipeedal tracks of an ancient hominant. These footprints come from sediments that date to around 6 million years old, very similar to the age of Auroran. This is a sick find cuz it might be direct evidence of bipedalism in early hominins. But I said maybe because the identity of these footprints is not entirely known for sure. Not all
25:43
researchers agree. What else would you expect? The prince might have been left by an ape of a different lineage. And it's hard to tell from the footprints if they were actually good at walking upright. And obviously, they're also very far away from where Aurora was found. Cre and Kenny are like 2500 m apart. So, there's a good chance the footprints don't belong to Auroran. But with the hips of Auroran having a similar structure to ours, and those footprints showing a potentially
26:02
bipeedal gate, there's some tantalizing evidence that early hominins might have already been walking on two feet by 6 million years ago. But maybe while being bipedal, Auroran was also maybe a climber. The shape of its arms and hands, including the curved bones of the fingers, are similar to those of modern chimpanzees and other climbing fossil apes. Like Sahalanthropus, Auroran seems to have lived in the woods. The sediments of the Lucino Formation formed on an ancient flood plane near a lake.
26:25
But the fossils found there, including ancient species of monkeys and impalas, provide evidence of surrounding forest. That forest might be where Auroran found its food. It had small round mullers that it probably used for chewing up plant material like fruits and leaves. The mers are also interesting because they're smaller than other apes, but they're also smaller than later hominates. Osteolipopithesines which evolved later in the hominin lineage had relatively larger mers and a relatively
26:47
smaller body. Based on the leg bones researchers estimate Aurorin was comparatively large standing just over 3 ft tall and weighing somewhere between 80 to 110 lbs. So Auror isn't just a perfect intermediate between earlier apes and later hominins. It had a big body with small teeth while the lateralines had smaller bodies and bigger teeth. So this has led to some obvious more disagreement about where exactly Auroran fits on the homminin family tree. Maybe it's an early
27:10
offshoot from our direct homminin ancestors. Some scientists have suggested that Auroran and not the oropithesines might be a direct ancestor of modern humans since its teeth and legs have so much in common with ours. But that is a very controversial statement. So just putting it out there just to say it and that's it. Whatever the case may be, Sahilanthropus and Auroran give us some clues about what was going on in the first couple million years of homminin evolution. During the
27:33
late measine epic, it seems some of the characteristic features of our lineage began to develop. And like I said earlier, the story of human evolution isn't a straight line. Sah philanthropist and Auroran could be our direct ancestors. Or they could be close relatives of our direct ancestors, or they could be early branches of the homminin family tree that went off and did their own thing, like a cousin twice removed. Hominant evolution didn't progress from one species to the next.
27:53
It progressed from a diverse variety of early species to an even more diverse variety of slightly later species. Between 6 and 7 million years ago, the earliest hominins evolved smaller teeth and lost that canine sharpening arrangement. probably had to do with changes in their diet or their social structure. At the same time, changes to the structure of the hips and legs might have made it easier for those first hominins to stand upright. This might have been helpful as these apes carried
28:14
food around or strolled into more open environments. This debate is obviously going to continue for a while. Our early ancestors are such an exciting and important topic that lots of scientists have lots of ideas about how to interpret all these fossilized details. And the remains of these early hominins are incomplete enough that there are lots of open questions that we might not have the evidence to answer just yet. For now, these are our best insights into the earliest stages of homminin
28:35
evolution. Obviously, we need some more fossils, pronto, and maybe eventually we'll find even older members of our lineage. Who [ __ ] knows? As we move through the story of human evolution forward in time and closer to the origins of our own species, the fossil record becomes more complete and the hominins become more obviously homminant. So, I hope you're excited cuz the next few episodes are going to be a lot more complete [ __ ] We're going to get into more complete [ __ ]
28:56
Artipythecus, Oralopythecus, an offshoot called Paranthropus. So, I hope you're excited. This is just the first chapter, so I hope you stick around and make sure you're subscribed so you don't miss the next episode coming out in 3 weeks. But before then, I'm going to have some very exciting videos. First off, I'm going to be showing you my time with Save the Elephants in Kenya that I visited back in June, which was really sick. And I found myself in the air a lot more than
29:18
I expected. After that, we're going to be in October, which means I have some spooky specimen [ __ ] so be excited for that. Check out my Patreon in the meantime for behind the scenes updates on our Discord server. We're also doing live streams, polls, fun chitchats, etc. And for now, stay curious. The world has a lot for us to learn. See you. [Music]
Here to help you learn
Sign in to keep a private conversation with your course tutor.
Ask me anything about the material…
Sign in to chat