A Brief History of Life: Rise of the Humans

Today we’re going to conclude our miniseries
about the history of life on Earth by talking about the Cenozoic era, from 65 million years
ago to the present. Cenozoic means “recent animals,” which
makes sense, since it’s the era we’re still in. During the Cenozoic, animals and plants and
everything else evolved to the forms we know today. They didn’t all do it at the same rate,
though. Many groups of invertebrates – and even
some vertebrates – haven’t changed a whole lot since the end of the Mesozoic era and
the extinction of the dinosaurs. But for mammals, which had existed since the
early Mesozoic, it was time to take over the world. The Cenozoic is divided into three periods. The names of the periods have been switched
up a bit recently, but these days the era is divided into the Paleogene, Neogene, and
Quaternary periods. And each period is subdivided into even smaller
units of time, called epochs. So, first, the Paleogene period: It covers the time from the extinction of
the dinosaurs 65 million years ago to about 23 million years ago, and it’s divided into
the Paleocene, Eocene, and Oligocene epochs. The Paleocene, from about 65 to 56 million
years ago, came right after the extinction of the non-avian dinosaurs, and even the ones
that didn’t die out – the birds – took a big hit on the diversity front. The dinosaurs left behind huge ecological
shoes to fill. There were lots of feeding strategies and
body plans that suddenly weren’t being used. The place an organism fits in its environment
is its niche, and usually two animals can’t use the same one at the same time. With the dinosaurs gone, the mammals started
exploiting those niches. So that’s why mammals expanded a lot in
diversity during the Cenozoic, even though they’d existed since the early Mesozoic. By the Eocene epoch, from 56 to 33.9 million
years ago, mammals had diversified into some pretty neat forms – including orders that
still exist, like rodents and primates, but also some that don’t, like the enormous
and bizarre titanotheres and uintatheres. One little antelope-like mammal had even wandered
into the sea to become the ancestor of whales. The Oligocene, from 33.9 to 23 million years
ago, saw the introduction of carnivores – but not what we usually mean by “carnivores.” There were already animals that ate meat. I’m talking carnivora: the taxonomic order
of mammals that includes cats and dogs. There were also lots of different kinds of
rhinos all over the place. The Paleogene was warm. Despite the mass extinction, the climate carried
on more or less the way it had in the Mesozoic: balmy, with no polar ice caps. But all that was about to change, because
the continents were shifting. Antarctica drifted over the South Pole and
was surrounded by a cold current, which led to global changes in the circulation of the
oceans. Antarctica started to ice over. The later two periods of the Cenozoic, starting
with the Neogene, were characterized by the rise to prominence of one extraordinary life
form. It changed the course of evolution for every
species that encountered it. I’m talking, of course, about grass. Grass is so common that most of us probably
don’t think about it. It just…belongs on the ground. Always has. But grass is a relative newcomer to the evolutionary
scene. The first grasses showed up just before the
end of the Mesozoic, but the C4 grasses, so called because of the way they process carbon,
only showed up between 25 and 35 million years ago. Those are the important ones, and the major
changes they influenced mostly happened within the last 10 million years. Grass is so important because it’s hard
to eat. It’s tough, low in nutrients, and it has
little bits of silica incorporated into its tissues specifically to discourage herbivores. Technically called phytoliths, they’re basically
sand. And chewing on sand is less than amazing for
your teeth. Rather than not eating it, a lot of mammals
just got really good at chewing and digesting grass. They evolved teeth with high crowns more resistant
to being ground down. They evolved complex stomachs, like the four-chambered
arrangement in cows, to extract as much nutrition as possible. And they evolved long legs adapted to running
around in the new, open grassland habitats. Horses and antelope were the big winners in
the Neogene. But it wasn’t just them. Grasses have become so widespread that all
kinds of creatures depend on them for food – including us. We don’t eat the leaves with the sandy bits
in them, but most humans depend on grain like corn, wheat, and rice – all grasses. We also feed grass and grain to our livestock. That means, for the rest of the Cenozoic up
to the present, that the evolution of mammals was tightly bound to the spread of grassy
habitats. Paleogene herbivores had been mostly browsers:
animals that eat leaves from trees and shrubs. In the Neogene, they were outnumbered by grazers. The Neogene is divided into two epochs: the
Miocene and the Pliocene. In the Miocene epoch, beginning 23 million
years ago, the continents were already close to where they are today. Ocean circulation became more modern too,
which meant things were cooling down. The giant shark C. megalodon patrolled the
oceans. Grazers like horses and camels were all over
the place. And toward the end of the epoch, in eastern
Africa, a group of apes was learning how to walk on two legs. At some point before or during the Pliocene
epoch, from 5.3 to 2.6 million years ago, North and South America crashed into each
other. During the Pliocene, animals crossed the new
land bridge and switched up their places on the continents. Opossums colonized North America – and as
anyone who’s driven around here knows, they stuck around. Camels and bears moved into South America,
and they’re still there too. And in the Afar region of Africa, there lived
the early human relative Australopithecus afarensis. Australopithecus’s upright body plan was
adapted to a shifting climate. And by the end of the Neogene, that climate
was shifting quite a bit. Antarctica had already started to freeze into
the southern polar ice cap, and in the Pliocene the Arctic began to get chilly too. This was the first time Earth had had ice
caps for a long time, possibly since the early Paleozoic. So by the time the Quaternary period came
around, starting 2.6 million years ago, things were a little different from the mild times
that came before. The Quaternary period is divided into the
Pleistocene and Holocene epochs. You might recognize that last one as the epoch
we’re in now. The Pleistocene epoch, from 2.6 million to
twelve thousand years ago, is sometimes called the Ice Age. But it was more like a series of ice ages,
with ice sheets advancing over the Earth and then receding in dozens of cycles. The reason the ice sheets advance and retreat
in cycles has to do with minor, predictable variations in the Earth’s orbit. When the ice sheets get more sun, they melt
more than they freeze, and vice versa. Atmospheric carbon dioxide also tracks closely
with global temperature during these cycles. When CO2 drops, the temperature plunges, too. We coexisted with lots of cold-weather organisms
in the Pleistocene, like woolly mammoths, saber-toothed cats, and the actually-real-not-just-from-Game-of-Thrones
dire wolf. Many of these are extinct, even though we
aren’t. The post-mortem on the Pleistocene megafauna
seems to be some combination of the climate variations that caused the glacial cycles,
and the arrival of hungry humans with pointy sticks. So-called archaic humans, also sometimes called
Homo heidelbergensis, date to around 400,000 years ago. Then anatomically modern humans showed up,
a little less than two hundred thousand years ago. Homo sapiens – that’s us – also coexisted
with other branches of our human family tree, like the Neanderthals. We’re the only ones left, but for a while
there were a handful of different species of humans running around at the same time. These early humans hadn’t yet developed
the complex cultures and traditions that make us truly ourselves, but they mostly just needed
time. There’s evidence for art as old as 40,000
years. Our big brains probably evolved as an adaptation
to the unpredictable climate. With the glaciers coming and going, we needed
flexibility to survive. Also, tools and fire helped. We are technically still in the Pleistocene
Ice Age, in what’s called an interglacial period, even though we consider the Pleistocene
epoch to be over. The ice is supposed to return eventually – just
not yet. The most recent epoch, the Holocene, is a
tiny slice of time, covering only the most recent warm interglacial cycle. That’s just shy of 12,000 years ago. It’s not the formal definition of the Holocene
or anything, but that period of time also happens to correspond to humans learning to
farm and keep animals. We started this miniseries with life emerging
nearly 4 billion years ago. Two hundred thousand years of human history
isn’t much compared to that, and our actual recorded history – compared to prehistory
– is, on a geological scale, VERY short. We’re basically a blip, but even though
we’re a relatively young species, we’ve already had a lot of influence on Earth’s
geology through things like nuclear tests and our use of plastic. A group of scientists has argued that this
is enough to define the start of a new epoch within the last century: the Anthropocene,
or human epoch. The powers that be in geology haven’t adopted
this term yet, but it’s often used informally. So, welcome to the Anthropocene, the latest
slice of time in geologic history. Only took us 4 billion years or so to get
here. Thanks for sticking with us through this mini-series,
which was brought to you by our patrons on Patreon. If you want to help us make more series like
this, just go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow
and subscribe!


  1. Zing Ramen said:

    I'm a Christian (Catholic) that believes in evolution and supports the Big Bang theory on some behalf, and not all of us are crazy religious freaks lmao

    August 21, 2016
  2. Soufiane Artwood said:

    cattle decapitation's the anthropecene extintion , anyone ?

    August 21, 2016
  3. Mohsin Rasheed said:

    Is it Ok to use this series for my university's presentation ?
    Of course ! strictly for education purpose and intent.

    August 22, 2016
  4. Mohsin Rasheed said:

    i hope you don't terribly mind me plagiarizing your content because i can't come up with any thing better.

    August 22, 2016
  5. Time4sale said:

    is it just me or is the sound off? or is he sick?

    August 22, 2016
  6. ResortDog said:

    Graham Hancock thinks " Since 2007, compelling evidence has been published in leading scientific
    journals confirming that fragments of a disintegrating giant comet
    struck the earth around 12,800 years ago. The impacts set in motion a
    mysterious 1,200-year global deep freeze that caused worldwide
    extinctions of species. Established theories about the emergence of
    civilization cite the invention of agriculture and monumental
    architecture some 11,600 years ago—immediately after the freeze. In this
    controversial presentation, best-selling author Graham Hancock argues
    that archaeologists, by not accounting for the cataclysm, have gravely
    misinterpreted history. What the record attests to is not the sudden
    invention of technology, but a transfer of technology to
    hunter-gatherers from a more advanced civilization." or History is built on a foundation of sand.

    August 22, 2016
  7. ישו מציל said:

    God Almighty forgive our sins in the name of Jesus Christ our Savior

    August 22, 2016
  8. Alkaiser said:

    We're in the age where we wonder about why we have butt hair.

    August 22, 2016
  9. Austin Murre said:

    Don't worry guys, the ice age isn't comming back since we're warming the place up….
    Mmmmm nice and cozy greenhouse gasses!

    August 23, 2016
  10. Turandot29 said:

    Is he wearing make=up? I think he is wearing make=up!

    August 24, 2016
  11. MultiMemich said:

    We are living in Androidocene, or maybe they will call it something else.

    August 24, 2016
  12. Siddharth Singh said:

    How far from earth have earthlings died?

    August 24, 2016
  13. k98killer said:

    My Bible says dinosaurs still live in caves. Take that, science!

    August 24, 2016
  14. JayneCobb88 said:

    good job SciShow. Way to contradict yourselves.
    "smaller birds have an advantage in warmer weather"
    "north american ice age mega fauna died out when humans arrived"
    "the temperature increased and the continetal glacier recided"

    never mind your own logic nor the fact that asian and european mega fauna died out at the same time as the north american species but had been living with humans for tens of thousands of years.

    humans aren't responsible for everything that has ever happened in history. so double check your political bias next time and stick to the science.

    August 25, 2016
  15. TheTH1RSTzZz Lurkz said:

    Actually the first human race was founded in Europe 7000 years before the African skull was found..

    August 25, 2016
  16. Beast Boiii said:

    I'm just happy he shaved those pubes on his chin

    August 25, 2016
  17. George Bailey said:

    I can't digest grass easily. Thanks Obamasum!

    August 25, 2016
  18. Amanda Goldberg said:

    You and me baby ain't nothin but mammals, so let's do it like they do on the Discovery Channel.

    August 26, 2016
  19. TheLegend27 said:

    Guys dont beileve this Evolution bs, I have proof the Earth was created 6,000 years ago. Just read the bible and all will be true.

    August 26, 2016
  20. OldDustyAssNigga said:

    this planet is going straight to hell

    August 26, 2016
  21. Merecir said:

    There are some evidence that the last ice age could have ended by two asteroid/comet impacts happening roughly 1000 years apart, both hitting the massive ice sheets covering the northern hemisphere and thus causing gigantic flash floods and the seas rising several hundred feet in a few weeks.
    And there are also appearing new archeological evidence that complex human civilizations existed before 12.000 years ago, and the fact that we have thought civilization appeared 12.000-10.000 ago could be based on the assumption that the sea rise happened slowly over thousands of years.
    So when taking into account that the sea rising could have happened almost instantly, the possibility of lost civilizations (i.e "Atlantis") now appears to be much more likely. And the reason we previously have not found much evidence of such civilizations could be because they were located along the coasts, areas that now lie far below the surface.

    August 28, 2016
  22. mur38 said:

    Is he getting fat?

    August 28, 2016
  23. Volvith said:

    And then there were the horseshoe crabs, which were basically like: "We got this.", and evolved ONCE, and then just quit.

    August 29, 2016
  24. Volvith said:

    I once blew up a building with grass.

    August 29, 2016
  25. Volvith said:

    I have a question.
    What defines a race?
    At what point do two different races, through crossbreeding, become one?

    I ask this because there are still minor "races" of humans.
    We still have, of course, the Caucasians, the Negroids, the Asians, and kind of but also not Hispanics, etc.
    But based on DNA, people from, for instance, the himilayas have completely different ancestors than we did, albeit that they met up with some of ours along the way. (Some people argue that we even had some woo time with gorillas at some point, but i prefer just to not think about that. Also, thanks SciShow for actually featuring that.)

    Also, there are still tribes around the world, again, albeit very few, that have been cut off from the rest of the world for such a long time, that they might be classified as their own sub-race, just because of their isolation.

    My point is that there really is no generalizing once you get down to the bottom of it.
    The only real reason we generalize creatures like dinosaurs to such a degree, is simply because so very little specimen are left.

    So, again, i ask you.
    What defines a race, or a species even?
    Evolution is often too diverse to classify, and to general to name.

    August 29, 2016
  26. I agree with everything you say said:

    Thank you for saying 'niche' & not 'nitch'!

    August 30, 2016
  27. Adam Murphy said:

    The Anthropocene has been made official today!

    August 30, 2016
  28. EariosRandomness said:

    Great, now I want to temporarily live in the Afar region so I can tell people I come from afar.

    August 30, 2016
  29. Carl Horn said:

    I think we are living in the Grasspocene. Maybe a better way of looking at it is they domesticated us to form complex civilization using fossil fuel to clear away other competing plants and expand the kingdom of grass?

    August 31, 2016
  30. Alicia Page said:

    A Mauricio Anton drawing here!! He is the father of a good friend!!!! Hahahahaha that was pretty weird!

    Congrats for the video

    August 31, 2016
  31. smitemus said:

    Whales came about from Antilope like creatures… O_O wwaaat

    September 1, 2016
  32. Dan James said:

    An interesting and informative series. However, I find the way you've edited out the pauses between sentences to be extremely annoying, and I don't understand why you've done it. Do you really think that people's attention will wander if they don't get the brief gaps that occur naturally in human speech? Are you trying to impart a sense of urgency which the subject matter does not need or deserve?

    September 1, 2016
  33. agutierr1 said:

    amazing! please do more mini series

    September 1, 2016
  34. Curtis S. Arnold said:

    I have a question, an experiment actually. Question being is an insects size proportional to the ammount of oxygen in its atmosphere? And if one increased said O² levels, would the insect grow larger?

    September 3, 2016
  35. Smitty said:

    please use the term carnivorans in the future. thanks!

    September 4, 2016
  36. Punya Pratyusha Sethi said:

    cool videos! great job simplifying otherwise complex stuff 🙂

    September 4, 2016
  37. Rafaella said:

    this is so cool and I learned so much

    September 5, 2016
  38. Joe Martin Vail said:

    I feel that I should mention something. In the Paleogene period, for the first few thousand years, there evolved giant birds that ruled that time. Eventually yes, the mammals said "fuck you, we want the limelight" and did take over, but the birds were rulers for the first few thousand years of the Paleogene era. Just thought I should mention that.

    September 6, 2016
  39. Tacet said:

    Okay, I'm absolutely convinced now that all our fantasy novels are actually about the last Ice Age. Dire wolves, multiple different humanoid species coexisting, and I'm sure I could poke around and find a creature that looked like a dragon if you squinted hard enough.

    September 7, 2016
  40. Andy said:

    the host is a cutie.

    September 7, 2016
  41. Husky said:

    Make a Space series

    September 11, 2016
  42. arianna thomas said:

    he's hot

    September 13, 2016
  43. Adam Collier said:

    1:11 Does that thing have pincers!?

    September 14, 2016
  44. Darkin said:

    i reeaaalllyyy wanna know what will happen after humans go extinct or when the next period arrives

    September 14, 2016
  45. tyler roost said:

    Why not cover Homo Erectus, the longest surviving hominid

    September 15, 2016
  46. Tarek Chamas said:


    September 15, 2016
  47. Tarek Chamas said:

    in short complex life was because some cell decided to put another one inside it (basically a fetish) and grass is our god 😀

    makes u feel kinda weird

    September 15, 2016
  48. MayCrafter 1522 said:

    There were multiple species of humans?!

    September 15, 2016
  49. Vebjørn Humblen said:

    Global warming is FAKE! We are still in the Pleistocene Ice Age! RIGHT?!!?

    September 17, 2016
  50. Sean Chua said:

    Were there any giant sea turtles in the Cenozoic Era?

    September 17, 2016
  51. Lammy Romernous said:

    Oh my God you guys JESUS is gonna be so freaking pissed by this! Did he die for NOTHING?

    September 17, 2016

    U made me feel like 1 year wuz 1 minute

    September 20, 2016
  53. LMacNeill said:

    So for the past 2.3 million years, we've been cycling back and forth between glacial periods and inter-glacial periods… Before that, the earth was a LOT warmer, for a VERY long time, apparently. And people are bitching about global warming, why? Seems to me that life was a lot easier when the Earth was hotter…

    September 21, 2016
  54. Lord_Lazy said:

    "invertaberates and even invertaberates" imao

    September 25, 2016
  55. Charles said:

    if we are in an inter-glacial period would not a bit more warming be better for survival than a cooling period??

    September 26, 2016
  56. CAPT SEA BEARD said:

    As a hunter. I just fantasize about shooting all of this different beasts. What a shame they're gone.

    October 1, 2016
  57. Musa Bashir said:

    DO A PREDICTION VIDEO ABOUT THE NEW EPOCH! Think of it as a hypothesis for the experiment of life

    October 4, 2016
  58. maxwell theobald said:

    I have a massive problem with the idea that we only learned about agriculture 12000 years ago. There is so much evidence of a globally interactive culture that shared language and technology before that time. A massive cataclysm destroyed most of it but, the meek inherited the earth. We're the descendants of the survivors of that cataclysm.

    October 5, 2016
  59. Denzil Alexis-lewis said:

    loved every minute of it sad to see it end

    October 21, 2016
  60. s l said:

    enjoyed this video

    November 15, 2016
  61. Mistah Bryan said:

    Grass now has a Predator of its own….



    December 11, 2016
  62. Y E E T said:


    December 12, 2016
  63. Vault Door said:

    Fantasy time… Let me just grab my popcorn. Wow, I believed this stuff one time.

    December 15, 2016
  64. itchy robot said:

    ghaaa! Not Michael Aranda again 🙁 ditch this guy.

    December 27, 2016
  65. itchy robot said:

    can't watch this douche 🙁 really interesting videos, ruined.

    December 27, 2016
  66. Camous said:

    Enough of this musty old Cenozoic. I hereby dub this new era the Technozoic.

    December 31, 2016
  67. Captain Redbeard said:

    So basically all those ice ages happened and then we were like "TWELVE IS ENOUGH." and figured out how to play with the thermostat.

    January 23, 2017
  68. Togher01 said:

    When you study the subject you really get to know now much SciShow dumbs the contact down.

    April 11, 2017
  69. Chase Davidson said:

    Wait, there's going to be another ice age? WE HAVE TO STOP AL GORE BEFORE HE KILLS US ALL!!

    May 13, 2017
  70. Alejandra Contreras Calcaneo said:

    I wonder what species are going to take over the Earth when mammals go extinct…

    June 1, 2017
  71. Izzy SciFi said:

    Welcome to the anthropocene, a time defined by how badly humans have fucked up the Earth in less than 12000 years, when mother nature usually has the same effect over a few million years.
    Bravo us

    June 17, 2017
  72. Meganopteryx said:

    Sharks are older than trees.

    June 23, 2017
  73. ĐÂŅÝŁ ĢÁŁÀ said:

    UR channels ur vids are sooo Dam amazing. Love u guys Man!

    July 2, 2017
  74. ShotgunLlama said:

    Alright well I'll check back in about 100,000,000 years for part 5

    August 4, 2017
  75. Laura A said:

    Michael Aranda is so relaxing

    September 7, 2017
  76. Foxy Supper said:

    Great Job!

    September 8, 2017
  77. Broockle said:

    I gotta thank you for pronouncing Niche properly. I really appreciate it

    October 2, 2017
  78. Lorenzo Perez said:


    October 13, 2017
  79. Lorenzo Perez said:


    October 13, 2017
  80. Greendude0101 said:

    The tail weapon on a stegosaurus is called a thagomizer… after the late Thag Ug

    November 25, 2017
  81. Da Dude said:

    i cringe when i hear that some animals haven't evolved.
    that's not true. crocodiles look similar to that of crocs 100 million years ago, but their anatomy has changed. their behavior is different. crocs have evolved.

    December 4, 2017
  82. William Bertels said:

    When you start noticing images and diagrams used in other scishow videos…

    December 6, 2017
  83. Igglybuff Quits said:


    December 17, 2017
  84. Aquarium Fuzz said:

    For a second there, I was thrown off by the bear labelled "marshmallow". (I realize it was just an image credit.)

    January 7, 2018
  85. Daniel McDavid said:

    this miniseries is great, you just didn't say "non-avian" nearly enough

    January 31, 2018
  86. Banana Shark said:

    this series was very well done thank you guys!

    January 31, 2018
  87. Edmund Osborne said:

    Humans = next mass extinction

    I can imagine that the organisms that survive the human era will make a similar video in a few million years, talking about how an intelligent species nearly destroyed all life on earth.

    February 17, 2018
  88. Matthew Ray said:

    4:42 – I didn't know Godzillas came from North America! 🙂

    February 21, 2018
  89. Mar Rus said:

    But I'm allergic to grass 😨

    March 8, 2018
  90. Michael Jordon said:

    Is it hard to believe​ a javelin looking thing became a whale

    March 19, 2018
  91. Ashir Malik said:

    FUN FACT: Dinosaurs are not actually big lizards, they are always found with feathers!

    April 18, 2018
  92. Joshua Harrison said:

    thank god – finally a correct pronunciation of niche by a sci show presenter …

    July 3, 2018
  93. ADEpoch said:

    You guys rock!

    August 4, 2018
  94. jmm1233 said:

    all the beasts got big and huge and humans were like 'will real silm shady please stand up'

    December 7, 2018
  95. Lia Estrella said:

    All these millions of years and I'll barely reach 100.

    May 3, 2019
  96. Jan Silver said:

    good reasonable points!!!

    May 12, 2019
  97. Havier Blakeowens said:

    this is amizeing

    May 23, 2019
  98. kyler buck said:

    you forgot to tell us how mammals survived and dinasours didn't

    July 1, 2019
  99. Smokey said:

    Pure fiction, complete fairytale taught to kids. What rubbish. No science here

    November 6, 2019
  100. Richard Landrum said:

    I wonder if the period of time containing multiple kinds of humans is related to the folklore of elves, dwarves, hobbits, orcs, and gnomes.

    November 21, 2019

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