Human Evolution
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So we’re about halfway through our series, and 6.0 after five episodes involving no humans whatso- ever, today we are finally going to get some people! HUMAN Mr. Green, Mr. Green! Why are we already at hu- 0:49–1:39 manity? I mean, if we’re covering 13.8 billion years, RISE OF HUMANS shouldn’t humanity come in the last, like, two sec- EVOLUTION onds of the last episode? I mean, humans are totally insignificant compared to the vastness of the uni- verse. Like, we should be checking in on how Jupi- ter’s doing. Fair point, me from the past. Jupiter, by the way, still giant and gassy. There’s two reasons why we focus a little more on humanity in Big History. The selfish reason is that we care about humans in Big History because we are humans. 0:00–0:49 Hi, I’m John Green. Welcome to Crash Course Big We are naturally curious to figure out where we History where today we’re going to talk about the belong in the huge sequence of events beginning OUT OF AFRICA Planet of the Apes films. What’s that? Apparently with the Big Bang. Secondly, humans represent those were not documentaries. a really weird change in the Universe. I mean, so far as we know, we are one of the most complex But there was an evolutionary process that saw things in the cosmos. primates move out of East Africa and transform the Earth into an actual planet of the apes. But Whether you measure complexity in terms of bio- the apes are us. And then we made the movie, and logical and cultural building blocks, or networks or then some prequels and some sequels and some connections, I mean, we’re kind of amazing. reboots, and now sequels to the reboots. Man, I can’t wait until I get to see the 2018 reboot of this episode of Crash Course Big History. I hear they get James Franco to play me. BIG HISTORY PROJECT 2 1:39–2:27 Now, I realize that many of our viewers will be Then somewhere around 40 million years ago, offended by our human-centric bias, but humans India, which had been floating around the south- ADAPTIVE RADIATION are amazing. I mean, we invented the Internet and ern oceans as an island, smashed into the Eur- we invented the animated GIF and we invented asian continent with such force that it created the Dr. Who, and then we invented Tumblr, a place world’s tallest mountain range, the Himalayas. where all of these things can come together. Meanwhile in Africa, primates continued to evolve, 3:03–3:40 So, 65 million years ago, catastrophe wiped out the and 25 million to 30 million years ago, the line of dinosaurs and we saw the adaptive radiation of a the apes diverged from the Old World monkeys and, DIVERGENCE tiny shrew-like ancestor of humans that would look no, neither you nor a chimp is a monkey, nor did more at home, like, next to a hamster wheel than in we evolve from the monkeys that are around today. your family album. Those are like our cousins. Let’s set the stage in the Thought Bubble. So, the Moreover, we did not evolve from chimpanzees. slow waltz of plate tectonics continued to pull Eur- The chimpanzee is a cousin, as well, not an uncle. asia and the Americas apart, expanding the Atlantic We are not more highly evolved than they are. Ocean. Primate colonized the Americas and, sepa- Instead, our lines of descent split off from a com- rated by the vast Atlantic, continued their separate mon ancestor with chimpanzees about 7 million evolution into the New World monkeys, which is years ago. Then chimpanzees further split into a not a band name, although it should be. separate species, the bonobos. 2:27–3:03 Then around 45 million years ago, Australia split Knowing about this common ancestry tells us a lot from Antarctica and, while mammals out-competed about our shared traits with other primates. For 3:40–4:10 CONTINENTS SPLIT most marsupials in the Americas — except animals instance, we all have fairly large brains relative to SHARED TRAITS like possums — Australia saw an adaptive radia- our body mass. We have our eyes in the front of our tion of marsupials. This of course meant that later, heads — from the days when we hung out in trees about 100,000 years ago, when the Americas were and depth perception was an excellent way of tell- having their share of mammoths and saber-tooth ing how far away the next tree branch was so as to tigers, Australia was having a spell of gigantic kan- prevent us from plummeting to our deaths — and we garoos, marsupial lions, and wombats the size of also have grasping hands to make sure, you know, hippos. that you could hold on to the branch in question. 3 BIG HISTORY PROJECT 4 Primates also have hierarchies — social orders, When it comes to intergroup encounters in the wild, whether male or female led — that determine who the male bonobos seem tense around strangers gets primary access to food, mates, and other ben- at first until, usually, the females from each group efits. Thanks, Thought Bubble. cross over and just have sex with the newcomers, completely diffusing the tension. Talk about make 4:10–4:58 So our closest evolutionary cousins, the chim- love not war. Bonobos are hippies. panzees, can tell us a thing or two about shared COUSINS behaviors. For one thing, while all primates have a While our common ancestor with the chimpanzees hierarchy of alphas and betas, humans and chimps, around 7 million years ago was more suited to liv- who share 98.4% of their DNA, are the most prone ing in forests and seeking refuge from danger by to team up together and launch a revolution against climbing trees, climate change in East Africa made the alpha male. things colder and drier and many forests were replaced by woodlands in wide-open savannah. We’re also both prone to ganging up, roaming our territory, and beating up unsuspecting foreigners Life in the savannah meant our ancestors needed 5:41–6:28 of the same species, and not for direct survival to run from predators rather than climbing trees, reasons. Chimpanzees have been observed finding so our lines shifted away from the bow-legged BIPEDALISM a lone chimp male from another group and kick- stance reminiscent of chimpanzees and developed ing, hitting, and tearing off bits of his body and then bipedalism, where our locomotion came from legs leaving the helpless victim to die of his wounds, that were straight and forward-facing. There’s still and humans definitely bear this stamp of our lowly some debate about when bipedalism first began, origin where, indeed, the imperfect step-by-step but we know that by the first australopithecines process of evolution made us highly intelligent but around 4 million years ago, our evolutionary line still with prefrontal cortexes too small and adrenal was bipedal. This also freed up our hands. glands maybe too big. Australopithecines were not very tall, standing only Aggression and bloodlust are definitely part of our just above a meter, or just over three and a half 4:58–5:41 shared heritage, and looking at more recent human feet, and had brains only a little bigger than modern SHARED HERITAGE history, does that really surprise anyone? Contrast chimpanzees. They were largely herbivores with that behavior for a moment with the more peaceful teeth adapted for grinding tough fruits and leaves. bonobos, who are female-led and, when a male in a group gets a bit pushy, the females are prone to gang up and teach him a lesson. 5 BIG HISTORY PROJECT 6 Australopithecines may have communicated through Similarly, as impressive as Homo habilis’ stone- 7:15–7:56 gestures and primitive sounds, but their higher working abilities are, we see very little sign of larynx meant that they couldn’t make the range of technological improvement over the thousands and TOOLS AND FIRE sounds required for complex language. There was thousands of years that habilis existed. probably a lot of pointing and grunting going on, kind of like me before 6:00 a.m. Same goes for Homo ergaster erectus, who was around 1.9 million years ago. Homo ergaster erec- 6:28–7:15 By 2.3 million years ago, Homo habilis arrived on tus had an even bigger brain, was taller, and they the scene. They weren’t much taller than australo- even seemed intelligent and adaptable enough BIGGER BRAINS pithecines, but they had significantly larger brains, to move into different environments across the though still a lot smaller than later species. old world. They may have even begun our first clumsy attempts at fire, which is vital for cooking Excitingly, Homo habilisis known to have hit flakes meat and vegetables, opening up opportunities for off of stones to use them for cutting. Now, lots of more energy and even more brain growth. But still, species used tools. For instance, chimpanzees there’s not much sign of technological improve- use sticks for fishing termites out of the ground, ment. Their tools got the job done — if it ain’t broke, and they use rock hammers and leaf sponges and don’t fix it. branch levers and banana leaf umbrellas. A lot of these skills don’t seem to arise spontaneously just Yet, 1.78 million years ago, we do see Homo ergas- 7:56–8:41 because of the intelligence of individuals, but, like ter creating a wide range of tear-drop hand axes in in the case of termite fishing, chimpanzees pass Kenya.