in 1799 a strange animal skin landed in the hands of biologist George Shaw studying its features Shaw noticed the perfect resemblance of the beak of a duck engrafted on the head of a quadraped so accurate is the similitude that at first view it naturally excites the idea of some deceptive preparation by artificial means so basically this thing seriously looks like a duck bill sewn onto some fur that animal the Platypus is very much real and even weirder than sh realized platypuses lay eggs they sweat milk through their skin and they're venomous to boot they're also mammals like us but they're a different kind of mammal one that split off from the rest back when the dinosaurs were still around today they are one of only two living members of that weird wonderful lineage we call the study of branching evolutionary histories like these philogyny understanding it helps us paint a picture of our pal the Platypus like who their an aners were and why they look so distinguished today and beyond that philogyny helps us understand all kinds of lineages to make sense of life's big whopping family hi I'm Dr Sammy your friendly neighborhood entomologist and this is Crash Course biology I'm I'm sorry I I didn't get enough theme music last [Music] night [Music] life's extended family is full of second cousins you've never met and great uncles twice removed nobody's wearing name tags and there's no Auntie with an encyclopedic memory to tell us how we're related but we humans make and share knowledge about the World by naming and categorizing stuff whether that's movie genres art styles or types of burritos we slot name tags on life's diversity through taxonomy systems of labeling and categorizing organisms for over 250 years biologists have largely used the lenan system of classification it files living things into groups called taxa based on observable traits that they share the sortings are basically a bunch of nested boxes species goes in genus genus in family family in order and so on but these taxonomic boxes are kind of subjective boxes like genus or family for example can be very broad or very specific depending on when in history they were coined I mean there is literally one family France more than 12,000 species but just one family whose idea was that and because lenan taxonomy often relies on physical traits to sort organisms it can miss other less visible markers of relationship between species inter systematics the science of categorizing organisms based on their philogyny that fancy word for evolutionary history unlike lenan taxonomy which rested on how we humans historically named things systematics Works to uncover more objective data about how species are related biologists construct philogynes by comparing the anatomy and DNA of different organisms for example sometimes organisms have common features because of shared ancestry called homologous traits homologous comes from the Greek homologos which means consistent and with homologous traits you see a consistency in The evolutionary blueprint like if a horse a bat and you walked into an x-ray machine and and no this is not the setup for a terrible joke you find the same basic bone structure in your arm the horse's front legs and the bat's Wing different Arrangement same hand-me-downs from a common ancestor but if you put a bird and a dragonfly in there you'd see that their wings aren't made from the same stuff they have totally different evolutionary origins and so Wings between those organisms are not homologous structures but it's not always that simple to determine how organisms are related giant pandas also share their basic arm bone structure with us plus a Thum like appendage so you might look at a panda paw and think boom Samesies we're close relatives and while our thumbs do perform similar jobs like firmly grasping snacks our jointed thumb consists of several bones a panda's thumb is actually a single wrist bone that evolved into a lengthened hook so these are analogous traits they look similar but evolved independently it's also why pandas can't play video games so in addition to comparing physical similarities biologists will use genetic similarities to construct philogynes this is based on the hypothesis that life runs on a roughly regular molecular clock meaning DNA and protein sequences have evolved at a relatively constant rate over time so theoretically the more genetically different two species are the more time has passed since their most recent common ancestor some models of assume that the rate of change varies across time and organisms but averages out to a fairly steady Rhythm other models assume that the rate has evolved in step with other traits like the rate at which an organism metabolizes his food but either way the point is we can compare apples and oranges genetically anyway now some genetic differences arise from natural selection because they're traits that lend an advantage or disadvantage as an organism evolves but others they've Arisen due to sheer Rand chance let's pay a visit to the theater of life even as a kid Japanese biologist and geneticist Dr Moto Kimura wasn't afraid of thinking differently he was outspoken brimming with questions even when they rubbed his teachers the wrong way so it's no surprise that Kimura went on to ask a really big question in 1968 what if evolution isn't entirely about survival of the fittest but also survival of the lucky complex math LED Kimura to suspect most genetic changes are random and new neutral they don't impact whether the organism does better or worse in their environment he called this idea neutral Theory and argued that sheer chance had a bigger effect on Evolution than natural selection this was very different from what Charles Darwin had proposed and how most biologists thought Evolution worked so it didn't go over well at first but Kimura defended the idea with dogged determination and by challenging one of Darwin's basic ideas kamur refined our understanding of evolution he showed us random chance does play a role a role so big that it's now typically assumed to be the reason for a genetic change unless we have strong evidence for selection he even won the Darwin medal for his efforts the first Asian biologist to receive the esteemed award and one of his most vocal critics presented it to him with a smile because even when biologists don't agree on everything we often Delight in the discussion and in growing our knowledge of Life biologists today still debate kamora's ideas and apply them to inform their understanding of the phyes of different species and these are often visualized with philogenetic trees these Nifty diagrams were created way back in the middle of the 1800s and popularized by Charles Darwin they represent hypotheses about organisms ancestry including how groups have diverged or Grown Apart and who's most closely related to whom like you might not expect a tiny Canary and a toothy crocodile to have much in common but there are lots of traits that connect for starters birds and Crocs both have a four chambered heart they also both build nests keep their eggs warm and sing I mean to be fair a crocodile song is more like a yell but just like canaries it uses its voice to crw to lovers and tell competitors back off and none of this is a coincidence it's because birds and Crocs are each other's closest living kin and you can see this relationship Illustrated on a philogenetic tree evolutionarily speaking speaking Crocs are closer to birds than they are to other reptiles like lizards or snakes and whatever traits birds and crocodiles share it's likely that their most recent common ancestor and other descendants of it had those traits too including dinosaurs now we're probably not going to find fossilized dinosaur hearts or vocal recordings to confirm this but we do have fossils of nest building egg protecting feathered dinos and a pretty strong hypothesis so let's learn to read one of these puppies take the philogyny of the eight species of bear each line or Branch represents a distinct lineage polar bears sit at the tip of this branch and brown bears at the tip of this one their branches connect at this little joint or node representing their most recent shared ancestor think of that node as an ancient population of bears that were neither polar nor brown bear but the latest ancestor of both species we don't necessarily know exactly who they were or what they looked like so they're not pictured here just just represented by this little node brown bears and polar bears are what's considered sister taxa that is two descendants of a shared ancestor and if we imagine slicing off their little chunk of the tree we can think of them as a cla a group including the ancestor and all of its descendants zoom out and we can group organisms in broader clades like snipping at this note groups brown bears and polar bears with four other bears and their more distant common ancestor and if we go back in time even further further we find a more distant ancestor and we add spectacled Bears to the mix new clay alert and still deeper in the past giant pandas split away from the other Bears forming a weird little Branch all their own but they're still within that Big Bear clay by the name of URS because they descended from the same bearish ancestor as the others giant pandas and red pandas you might notice go by a similar common name and sit near each other on our tree but they're not each other's closest genetic relatives the clue is the node nearest the red panda Branch shared with raccoons that's the most recent ancestor that red pandas share with another species phylogenetic trees like this one can be drawn vertically horizontally or even diagonally like this tree shows evolutionary relationships among fish frogs lizards mice and humans who all have a common ancestor way back when but we humans share an ancestor with mice more recently than with fish so you've got more to talk about with the rodents at the pet store than the Goldfish and that makes some sense but it might come as a surprise that water loving frogs are more closely related to people than they are to fish and that's because frogs and fish's most recent shared ancestor lived longer ago than the shared ancestor of humans and frogs and Beyond telling us how organisms are related philogyny can also help us answer cool questions like where did feathers come from we've seen traces of feather-like appendages on dinosaurs from the Cretaceous Period and scientists believe that the first feathers capable of sustaining flight developed on a dinosaur bird ancestor a little further along the evolutionary tree but there's no hierarchy here no ladder from primitive to advanc no matter how far back in time we go it's more like the deeper we look back at the philogenetic tree of the Bears the more unbe likee their ancestors were or maybe it's that bears became less bacterial likee no judgment for me either way because there's no top dog or bear in evolution just many different ways of accomplishing survival so philogenetic trees represent hypothesis about how those ways of living evolved and they are regularly updated when scientists make new connections meanwhile life as always is more complicated than we can ever truly capture for example these branches aren't as distinct as they seem some closely related branches can still interbreed like those polar bears and brown bears that we met earlier they've been known to mate in the wild producing Grizzly polar hybrids called pisle or groller bears pretty good Hunters but not strong swimmers we see similar evidence that many organisms change on a population level as a result of moving around and breeding with other populations what's called gene flow so it's not enough to think of life's branches as only splitting off from common ancestors because the distinctions between branches are fuzzier than that branches can link back up again genes can also flow between species so while we often do think of life's evolutionary history sort of like a tree it's also like a network of streams winding and Meandering as species grow apart but sometimes find their way back together again constructing the philogynes of different species helps us make sense of Earth's big ongoing extended family with all of its weird and wonderful offshoots it helps us Trace connections between living things comparing what they share and how they differ and it helps us understand how all life evolved and visualize How Deeply interconnected we are in our next episode we'll scope out a great view of the Tree of Life when we talk about biological diversity I'll see you then peace this series was produced in collaboration with hhmi biointeractive if you're an educator visit biointeractive.org g/c crashcourse for classroom resources and professional development related to the topics covered in this course thanks for watching this episode of Crash Course biology which was filmed in our studio in Indianapolis Indiana and it was made with the help of all of these nice people and if you want to keep crash course free for everyone forever you can join our community on patreon [Music] bye