Human Evolution: We Didn't Evolve From Chimps: Crash Course Biology #19

at some point around 300,000 years ago a brand new species of ape made its debut Homo sapiens the new crew of upright Walkers would eventually go to paint the lco caves build Machu Picchu and invent credit scores hey not everything can be a hit but before all of that homo sapiens that's us by the way were just the scrappy New Kids on the Block joining at least three other close ape relatives already walking the Earth we think that they were a lot like us some of them learned to control fire and started cooking their food and later some of them even buried their dead and made art just like we eventually did we might like to think of ourselves as the fire wielding toolmaking stars of this story called Humanity but for nearly 90% of our species time on this Earth we've had company and those long ago neighbors complicate the idea of what makes a human well human hi I'm DrSammy your friendly neighborhood entomologist and this is Crash Course biology Alas poor theme music I knew you [Music] well some scientists only use the word human when talking about Homo sapiens but some scientists use human to refer to other species within the homogenous as well including those close relatives that we share the planet with which leaves us with the burning question what is a human well for starters all our closest kin have been extinct for at least the last 40,000 years so today we humans have more in common with chimpanzees and bonobos than any other living species we share about 99% of our DNA with them in fact chimps are more closely related to us than they are to their gorilla cousins humans and chimps are both members of the large primate group with which includes our distant cousins like lemurs and Tarsiers and also some not so quite distant ones like gorillas and orangutans but humans didn't evolve from chimps or any other living ape for that matter chimps and humans split from a common primate ancestor around seven million years ago and we've each been moving along our own evolutionary branches ever since then alongside many other branching species some that survive to today and many that didn't so yet there's no straight line from chimps to humans but there are a lot of branching ones and there's still a lot that we don't fully understand about our Branch the hominins we know of at least 20 other hominin species from fossil and DNA evidence that have lived across the past 7 million years but we're still working out how those hominins are related to each other and to us like they're all your relatives but they're not all your ancestors sort of like you didn't descend from your grandma's sister but she's still part of your family love you you great auntie we do have a good hunch that one of those fellow homant Australopithecus afarensis was basically Humanity's Grandma Lil afarensis lived about 4 million years ago in Africa they were only 1 M tall with arms longer than their legs and a small brain and based on the clues from fossilized hips skulls and Footprints we think afferences did something that at the time was a little odd for Apes but has since become pretty common place for humans walk around on two legs a another likely human ancestor Homo erectus shredded their stuff starting around 1. 8 million years ago they had ahead about twice the size of aphereses with body proportions roughly equivalent to modern humans great for long-distance walking in fact they were the first homin to make the long Trek Out of Africa and hang out in Europe and Asia kind of like the original Gap your Backpackers while these two ancient ancestors shed some light on how early humans lived most of our relationships with other hom remain murky and debated the more we learn about the homin family tree the more we realize it might not be much of a tree at all let's take a trip to the theater of life in the 1990s the Chinese paleontologist DrZen Shi Wu found himself puzzled over a 200,000 year-old skull called the Tali Cranium thick and heavy brow with a medium-sized brain in some ways it looked like Homo sapiens fossils from Europe but in other ways it resembled fossils of homo erectus from China basically it was a real mixed bag so DrWoo came up with the hypothesis what if this species wasn't just another branch of the evolutionary tree what if Instead This was a sign of evolution working like a braided stream with population sometimes trickling and drifting away but then eventually merging back again into the same flow he imagined a pattern like this when populations become isolated for Generations which means not reproducing with Outsiders they become different and evolve distinct traits but sometimes s those populations link back up and swap genes again and those genetic differences start to give way to similarities once more with these es and flows populations alternate between times where they're apart drifting on their own course and times where they're connected with a steady flow of genes between them DrWoo originally used the braided stream analogy to think about how human evolution played out in China but today many scientists agree it's a useful model for thinking about how humans evolved across the planet and how Evolution Works in general with better technology scientists have been able to extract ancient DNA from fossils and they've learned that one part of the braided stream analogy is spoton ancient humans got busy making babies with other hominins as they spread across the globe our ancestors interbred with neander tals some of our other hominin relatives who emerged around 400,000 years ago much like us neander tals buried their dead and made art because of those prehistoric relationships many people today are walking around with a little neander tal in them about 1 to 4% of their DNA but are humans and neander is the same species well not exactly you see some areas of science defined species based on the ability to interbreed and produce fertile offspring and by this definition you and neander seem like one and the same but when scientists talk about fossils we typically use different definitions the morphological and philogenetic species concept which focuses more on physical features and ancestry to draw lines between species so scientists typically consider neander tals and humans different species or at least different subspecies you can learn way more about the trickiness of defining species boundaries in episode 15 in any case it wasn't only neander talls that caught our eye we also interbred with another of our ancient relatives the High Altitude adapted Denise events and because of that some of us today are better at handling low oxygen mountain top tops thanks to a genetic variant that came from that inter breeding so the big hominin family tree or stream is one we're still waiting through scientists connect the dots through fossils genetic evidence and some major snooping on our ancient relatives like 3 years deep into their Instagram at 2 a. m.

levels of snooping and that helps us Trace some of the major leaps that we've made on our way to becoming human like remember our friend granny afarensis who walked around on two legs well we know they got around that way thanks to fossils and biological anthropology we can see that the spinal cord passed through early homin skulls near the bottom rather than the back as it does with most Apes that means the hamin's head stacked above their body a position that comes with walking on two feet rather than all fours walking on two feet freed up the front limbs which we can tell happened before the invention of Photography because what are we supposed to do with these on camera just Anyway by 2. 5 million years ago go our ancestors were busying themselves with some early inventions hammering rocks into tools that could slice meat off the bones of large animals think of it as the world's first kitchen gadget the oldest ancestor of The Slap Chop by 1. 8 million years ago our ancestors had roughly the same body size and shape as we do and they were walking long distances on two legs like our friends Homo erectus who migrated For the First Time Out of Africa and as our relatives walked to new places they faced new challenges and evolved bigger bodies brains to cope with them by about 1 million years ago some of them had mastered fire which we know from piles of ancient ash left behind in caves with fire came the first attempts at cooking which really makes you wonder why it took us so long to invent Chicken and Waffles if we had a million-year head start and even though they weren't cooking up soul food Staples their brains were steadily growing all this time but things really picked up around 800,000 to 200,000 years ago when our ancestors started communicating with symbols sending messages with shared meanings which might sound like a no-brainer but it was in fact a very big brainer as early as 320,000 years ago they were fashioning red and black rocks into crayons possibly using them to decorate themselves or their tools they were also putting in the extra effort to transport special rocks over long distances modern humans finally arrived on the scene around 300,000 Years Ago by then our brains had tripled in size since the first tomin and ancestors started walking it's like The evolutionary biologist Steven J Gould said we stood up first and got smart later by 880,000 years ago some groups of wandering humans had migrated successfully across a number of continents but each time a group struck out on their own they eventually experienced the founder effect a dwindling of their gene pool which would lead to a loss of genetic diversity that's why to this day people in subsaharan Africa are more genetically diverse than anywhere else on earth is is because they're the descendants of all the people who stuck around rather than smaller groups that moved away at the same time people kept moving and mingling having babies with the locals everywhere they went and that meant there was a lot of mixing between populations even today there aren't any hard and fast genetic boundaries between groups of people as we spread across the globe different traits evolved based on what helped our ancestors live and reproduce in different environments the whole spectrum of human skin color arose to hit that sweet spot of blocking just enough but not too much sunlight people in less Sunny regions evolved paler skin to allow for more UV absorption in order to produce enough vitamin D but too much sunlight destroys folate a vitamin your body needs to make DNA so closer to the sunny equator people with more of the skin pigment melanin had an edge because of its ability to absorb excess UV radiation around 12,000 years ago humans started domesticating wild plants and animals selecting them for traits that we like by controlling their breeding that is with one pretty big exception dogs we had already been hanging out with dogs for thousands of years by then in fact we've been Pals with dogs for so long that it's not even clear who started it us or them and even today we're still evolving scientists aren't yet sure why Homo sapiens survived and none of the other homins did but studying human evolution helps us grapple with that big question and others like what even is a human and while there's not one single answer there are patterns sharing resources caring for each other's kids and receiving care as we get older to name a few that said a lot of what we are as humans doesn't come pre-installed we learn it together as we go the more we learn from our ancestors the better we understand ourselves and by looking at our past we can imagine our future not as a rigid already charted course but is a winding stream that has been flowing from Millennia and with a little luck we'll will keep flowing from Millennia to come join us back here for our next episode as we move away from Evolution and start talking about something equally as important but physically smaller carbon and the chemistry of life peace this series was produced in collaboration with hhmi biointeractive if you're an educator visit biointeractive.