For about a million years in the early Pleistocene
Epoch — from about 2.4 million to 1.4 million years ago — it was a really exciting time
to be a hominin. Hominins, you’ll recall, are the group of
human ancestors that are more closely related to us than to chimps and bonobos. During this million-year stretch, different
branches of our evolutionary tree were flourishing all over southern and eastern Africa. And if we were to zoom in on the earliest
part of this million years, we’d encounter a familiar face. Or at least a somewhat familiar face: the
face of Homo habilis. It stood just over a meter tall, and had a
slightly larger brain and smaller teeth than its earlier relatives, the australopithecines. But it still had longer arms and a protruding
lower face, traits that are usually considered more basal in the hominin lineage. And yet! This ancestor probably made and used stone
tools! In fact, Homo habilis means “handy man,”
and its discoverers gave it that name because they thought that it was responsible for the
many tools that had been found near its remains. But, does this hominin really belong in our
genus, the genus Homo? Was it more like us than its earlier ancestors? Over the last fifty years or so, the human
family tree has really filled out. We’ve discovered all kinds of new fossils
of our ancestors and relatives, like australopithecines that have about the same brain size and limb
proportions as Homo habilis. And this has led some researchers to question
whether Homo habilis is really a member of our genus at all. As more and more fossil ancestors have been
found, our genus has become more and more inclusive, incorporating more members that
look less like us, Homo sapiens. And this is an important problem to think
about. Because, there’s some consensus about who
belongs in our immediate human family — like us, neanderthals, and even the ancient, globe-traveling
hominin Homo erectus. They’re all agreed to be clear-cut members
of the genus Homo. But beyond them, there are lots ancestors
for whom we can’t find a home. And there is no official definition of what
constitutes a human, either, whether that means being a member of our genus, or our
species, or just being able to walk upright and make tools. So by getting to know these other hominins
— the ones who came before us, the neanderthals, and our other contemporaries — we can start
to answer some big, interesting, and difficult questions … ….questions about what it essentially means
to be human. When the first fossils of Homo habilis were
found by Louis and Mary Leakey’s team in the 1960s, they had a difficult choice to
make: Were these the remains of australopithecines? Or were they in fact the earliest known members
of our own genus, Homo? Traditionally, defining who belongs in our
genus has come down to which traits are considered “uniquely” human. And when the Leakeys were pondering Homo habilis,
they used a definition of Homo from 1955, which said that to be a member of the genus,
you had to have some number of features in common with the three members of Homo known
at the time: Homo sapiens, Homo erectus, and the Neanderthals. The Leakeys decided that Homo habilis shared
three important traits with the other members of our genus: It had an upright posture; it
was bipedal, and it had the manual dexterity to make tools. And, sure, Homo habilis had those three things. But in the decade after Homo habilis was found,
new discoveries of other human ancestors were made in the same parts of Africa, and they
had these traits, too. And these new finds were all of various australopithecines,
which were inarguably not part of our genus. The most of famous of these discoveries is
the specimen known as Lucy. Unearthed at Hadar, Ethiopia in 1974, she
was one of the most complete specimens of Australopithecus afarensis ever found. And she gave clear evidence of an upright
posture, like having thigh bones that angled inward toward the knee and a more human-like
pelvis. Then, four years later, a set of fossilized
footprints were found in Tanzania. Known as the Laetoli footprints, they were
probably made by Australopithecus afarensis, too — again showing that hominins were walking
on two feet more than a million years before Homo habilis was around. So if walking upright was not exclusive to
our genus, then the definition of our genus had to change. Instead of just physical traits, the thinking
then turned toward lifestyle adaptations as a way of defining who belonged in our group. Lifestyle adaptations are features that are
linked to how a hominin lived its life, like what it ate, how it got around, and where
it lived. For example, the increased brain size in members
of Homo was thought to be linked to a higher-quality diet, because being able to consume more calories
more efficiently has allowed for larger brains. And some researchers arrived at four specific
lifestyle adaptations that they thought might qualify a hominin for entry into the genus
Homo. Those adaptations included: an adult brain
size greater than 600 cubic centimeters; limb proportions similar to ours, with long legs
compared to our arms; the use of language; and the manufacture and use of stone tools. But still, these things only kind of applied
to Homo habilis. Because one of the most famous and complete
Homo habilis skulls, a specimen known as KNM-ER 1813, had a cranial capacity of only 510 ccs. Meanwhile, a big male specimen of Australopithecus
afarensis was found to have had limb proportions like those of early members of Homo — but
it lived 3.58 million years ago, way before Homo habilis appeared on the scene. And the capability for language can really
only be inferred from the fossil record. It’s pretty hard to tell whether Homo habilis
or any ancestor that lived millions of years ago was able to speak. That just leaves stone tools. And while researchers in the 1960s were pretty
convinced that Homo habilis was the maker of the tools at Olduvai Gorge, we now know
that australopithecines could likely make stone tools, too. So, let’s look at our group another way. Instead of talking about who might not belong
to our genus, let’s consider who might. Who were those other members of our genus
that lived alongside Homo habilis during that exciting, million-year span in Africa? And what can they tell us about the origin
of the Homo genus? Well, starting about 1.98 million years ago
in South Africa, there lived an australopithecine with distinctly Homo-like traits. Known from several relatively complete skeletons,
it was given the name in 2010 of Australopithecus sediba. Its discoverers placed it in Australopithecus
because of its small brain and long arms, but they also noted that it had small molars
and premolars, and facial features that were similar to other Homo specimens. So these researchers actually think that Australopithecus
sediba might be more closely related to our genus than other australopithecines are, but
other experts think it’s too recent in age. Another candidate for inclusion? Homo rudolfensis It’s been found at sites dating back 1.8
to 1.9 million years ago in Eastern Africa. The best fossil of this species is known as
KNM-ER-1470, and when it was discovered in 1972, it was originally classified as a large
specimen of Homo habilis. However in 1986 and again in 1992, further
studies found that its bigger brain, longer face, and larger premolars and canines made
it too different from Homo habilis to be a member of that species. But it was still assigned to our genus, because
of its big brain. At 775 cubic centimeters, it was well over
the classic 600cc cut-off. And finally we come to the first indisputable
member of our genus, and one of the most successful and widespread: Homo erectus. It lived from 1.9 million to just 143,000
years ago! The first Homo erectus fossils were found
in 1891, and some anthropologists later split this species into two – with Homo erectus
including the later African and Asian fossils, and the earlier African fossils being filed
under Homo ergaster. And experts generally agree that Homo erectus
is definitely a member of our genus. These hominins had modern human-like proportions,
were potentially capable of long-distance running, and generally had much smaller molars
and much larger brains than their predecessors. In other words, they were a lot more like
us than any of the other species I’ve mentioned so far. Homo erectus is also the first species that
we have fossil evidence for outside of Africa. They made it as far as China and Indonesia,
but their initial foray seems to have landed them in the Republic of Georgia, at a site
called Dmanisi that dates to about 1.77 million years ago. And the interesting thing about that site
is that there’s a lot of variation among the specimens found there. Some individuals from Dmanisi had the unmistakable
brow ridge of Homo erectus, but their brains were smaller than 600 ccs — the classic cut-off
for inclusion in the genus Homo. In fact, there’s so much variation in the
Georgian fossils that their discoverers made a case in 2013 for taking all of the other
early Homo fossils — including the ones assigned to Homo habilis and Homo rudolfensis — and
putting them in Homo erectus, lumping everything together as a single species. They argue that if the fossils from a single
site can show as much variation as we find between species, then all of those early groups
might as well be considered the same species. But of course, other experts disagree. They don’t think overall cranial shape is
enough to distinguish one species from another. To them, the devil is in the differing morphological
details of each skull. Now, with all this in mind, let’s go back
to Homo habilis. Where does it belong? Well, it doesn’t really seem to fit anyone’s
definition of our genus. And the best argument for keeping it in is
just that taking it out would require redefining what it means to be a member, which would
be a major taxonomic undertaking. Some experts have proposed lumping habilis
into the genus Australopithecus. Others say it’s neither Homo nor Australopithecus
and that it deserves its own new genus. So far, no single opinion has won out. Homo habilis remains a taxon in limbo. Ultimately, what defines our genus comes down
to how much variation in morphology, time, and space we’re willing to include in the
group we call home. In the past, an increase in brain size, a
bipedal gait, human-like limb proportions, and tool use seemed to have been enough for
inclusion. Those are the things that we thought made
us members of the same genus. But as we’ve discovered more and more hominin
fossils, our family tree has become more complicated, rather than less. So now, the latest research is suggesting
totally new ways to define our lineage. One new idea for a defining feature of our
genus? Tooth size! Smaller teeth generally indicate a higher
quality diet and the ability to prepare food with tools, instead of having to chew tough
foods for a long time. Another possible criterion is the pace of
our development. We modern humans have longer periods of childhood
and adolescence compared to our closest ape relatives, because we need that time to grow
our large brains and use them to learn. And we can track these growth patterns in
fossils by studying microscopic features of teeth. And as recently as 2015, some experts have
suggested that we should scrap the whole list of hominins altogether and just start from
scratch. They say we should step back and look at the
totality of the fossil record with fresh eyes to decide what traits we think are important
for being “human.” As it stands, there’s still no single way
to define our genus. Mostly it happens by comparison: Is a new
fossil more like what we’ve called Homo in the past or is it more like an australopithecine? And the jury’s still out on Homo habilis,
the species that started all the trouble in the first place. But if anything, the trouble really began
back in the Early Pleistocene, during that exciting million years or so when this group
of hominins first started to flourish. And it may be in the fossils from that time
— perhaps in fossils we haven’t found yet — that will help us better answer the question
of who belongs to our very exclusive group. Thanks as always, and extra big thanks to
our current Eontologists, Jake Hart, Jon Ivy, John Davison Ng and STEVE! If you’d like to join them and our other
patrons in supporting what we do here, then go to and make your pledge! Now, what do you want to learn about? Leave us a comment, and don’t forget to
go to and subscribe.

Author Since: Mar 11, 2019

  1. I think we should rethink the way we classify animals. Instead, perhaps we should use a vector-based approach. First, look at many humans. Each trait is given a vector value, like tooth mass, size, shape, etc. Plotting those vectors will place each person measured in an n-dimensional space. Once we've grouped a few thousand humans from around the world, the largest n-sphere that encompasses all those vectors is the region of homo sapiens. This will give a more numerical tool to help with us with taxonomy.

  2. I tend to skip these videos because they don't interest me as much as the animal ones do but now they are very helpful for an anthro class

  3. This says more about how 20th & 21st century humans think about and categorise things than it does about ancient human like beings themselves.

  4. I'm looking at their bones and I'm thinking to my self, these used⁰ to be alive and walking … I just wanna time travel to see them ❤🕧

  5. Please do a video on why us humans are Hairless monkeys in relations to other homonids… not in relation to other very hairy humans lol. And if us humans could have different eye, skin and hair colors, could the other homonids also have them. Perhaps we inherited from them via crossbreeding.

  6. All homonids are depicted as brown eyes and brown hair. I believe just like how all the old dinosaurs pictures were depicted as draped colors, which later turned out that they were very colorful. I believe that all homonids could have also been colorful: eyes, skin and hair. And this would just like with the old dinosaur colors lead to a complete colorful make over of old hominid images.

  7. what about some really crazy thing, like a cross-breed meaning that there is no real cut-off and the very last austrolop. actually could be called "homo basalus" or something – the very very last of them are actually super basic homo members

  8. Human brain is designed to save and self-secure. may this selfish adaptation is now became technology, that we are enjoying.
    We are the great killers with many super powers, 💬 enjoy your day.

  9. One day, we can determine what is consider hominins by what actually mated with homo sapiens through DNA evidence ;p

  10. Part of the problem is that nature is a continuum. You don't have a child born one day radically different from everyone else, add to that the general variations in different populations in different regions and you have your problem.

  11. Do you think that the origins of tales and descriptions of orcs, goblins, monsters etc. were based on humans interacting with H Erectus and Neanderthals?

  12. Is it possible that other species of humans were wiped out by pathogens?
    And if so, were those the same pathogens that infect us today?

  13. They have lived their lives millions of years ago,according to their environmental adaptations and nutrition available,our early relatives will continue to sway and baffle the brains of our scientists.Watch my music videos @Fleshoo/FLESHOO1.

  14. Sometimes i think where did we all get our language? How did we know how to talk but others doesnt speak the same language ? How did scientist know how long extinct creatures have lived for?
    What was there before the milky way or are we the only galaxy that have born first? Why do i exist? Why do we all exist? Why cant we all live in peace except fighting in war…? Why do we all have to suffer?

  15. Everyone I don’t think I’m human I have no ability to make any tools and I have no skills in speaking/writing

  16. There is a problem alright. Problem comes when you make an assumption and set out to prove it anything will be accepted. When that is proven incorrect instead of changing that assumption you continue with it.

  17. But if anything this trouble began whenever scientists determined certain things qualified these bones as humans. Then when that fell through they went from brains to teeth. When that falls through they will go to something else. Yet it's real now…remember…its real even if were wrong or constantly changing everything.

  18. Lets take the parameters for being Homo and reflect it on to K-9 (dogs). It would make no sense. Brain cc, posture etc. Dogs range such a variety that there should not be one catch all. However we still just group them and call them dogs.
    Let's face it, we are, on a galactic scale, just some other species' dogs.

  19. To take a step back and think, "and decide what traits we think are important for being human" – that sounds like a very meaningful exercise to do from time to time for any individual, not just paleontologists. 🙂

  20. The Humans before us were Mankind…
    They got older
    They were Stronger
    They were Wiser

    They were the gods on Earth back in those days..

  21. Hominids I learned about in school

    Australopithecus afarensis
    Homo habilis
    Homo orgastor
    Homo erectus

    Homo sapien neanderthalensis
    Homo Neanderthalensis

    Homo sapien

  22. It's all our fault that the rest of humans were wiped out. We pushed them to extinction just like we did to all the other megafauna.

  23. I would love support PBS and Eons … but my investment in science (with student loans) has left me broke and in debt so I'm unable to invest and support anyone other than myself … # Education should be a human right to self discovery, and not a crippling mortgage payment for a future career

  24. You keep showing like a bunch of pictures of really hairy ancient ancestor species and then casually slip in a random pic of a modern homo sapien running from hyenas. Maybe a little offensive?

  25. Hey every ancestor is people today say tht i m vegeterian..inshort there dna has gene which from nonvegeterian person.inshort there ancestor are nonvegeterian🤣😂

  26. If we found one remaining tribute of "ancient human" do we have to consider them as part of human kind therefore they got human rights?

  27. In ancestors the humankind ofyssey you can bang 2 rocks together and create a knife but you don' t need to be an australopethicus
    This is big brain time

  28. Didn't they have tools for vegetarian food? Like mortars? There could be a few types of Hominid near each other but if more than one of the types of these primates are carnivorous & made flaked tools, that would complicate things. Even scavengers fight each other.

  29. Why do we refer to different species of humans as “it” because without them we don’t exist so technically they are us well apart of us

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