Taxonomy: Life's Filing System - Crash Course Biology #19

Key Takeaways

taxonomy it's the science of classifying living things that sounds exciting today we'll basically be learning The Dewy Decimal System Of Evolution it's like filing I must be on the edge of your seat okay shut up when it comes down to it this science doesn't just categorize organisms when you look a little deeper you realize it's telling the story of all life on Earth and it's a pretty good story [Music] every living thing on this planet is related to every other living thing if you go far enough back we all have a common ancestor an organism that both you and I are descended from or something that a starfish and a blue whale are both descended from or even weirder that an oak tree and a salmon are both descended from that organism lived it lived very long ago but it was here and I dig that the trick of taxonomy is basically figuring out where all those branches of the evolutionary tree are and finding some convenient labels to help us understand all of these remarkable interrelationships let's be clear though taxonomy isn't about describing life in all of its ridiculous detail it's mostly about helping humans understand it because it's way too complicated without structure to get that structure biologists used the taxonomic system to classify all the organisms on on the earth it's sometimes called the philogenetic tree or the tree of life and it illustrates The evolutionary relationships between all living species so there are about 2 million known species but there could be anywhere from 5 million to 100 million species scientists really have no freaking idea new species keep getting discovered all the time and the more organisms we have to keep track of the more complex the philogenetic tree becomes so there's not always a consensus about how to classify this stuff there's lot of gray area in the natural world actually let me rephrase that the natural world is one giant gray area sometimes it's just hard to know where to put a certain group of organisms and eventually the group gets so big the classification system has to be messed with to make room for it so the system isn't perfect but it's good enough that we've been using it for around 250 years what's that do you smell a biography coming on [Music] Carl lus was a Swede born in 1707 and early in his career as a botanist he realized that the Botanical nomenclature of 18th century Europe was well just crap for instance in his day the formal name of a tomato plant was solanum C andme arbois patus Inus reimus simplicius lus actually said once I shudder at the sight of most Botanical names given by modern authorities not not only did the sloppiness bother him he saw a whole sugar storm blowing in cuz new plants were still being discovered in Europe but that was nothing compared to the crazy stuff that was coming from the new world lanaa saw that pretty soon naming conventions were just going to collapse under all these new things to name and then what so lus famously started off by naming himself he came from a peasant family and at that time surnames were just for rich people so when Carl went to college they asked him for his surname and he just made one up lenaeus after the Linden trees that grew on his family's Homestead Lenas got a medical degree and became a professor at Upsala University where he devoted himself to the study of nomenclature he had his students go to places and bring back specimens for him to study and categorize the method he eventually adopted was based on morphology or physical form and structure this wasn't necessarily a new idea back then people grouped organisms by analogous or homoplastic traits structures that appear similar but actually come from completely independent Origins by this definition Birds would be more closely related to butter flies than to reptiles because both birds and butterflies can fly but L has had a good mind for this stuff and turned to have a real knack for choosing actual homologous traits for his classification system traits that stem from a common evolutionary ancestor Lanas of course Didn't Know Jack about Evolution Darwin wouldn't come around for another 100 plus years but he intuited that some traits were more important than others for instance he was struck by the fact that reproductive apparatus seem to be a good way of classifying plants he also caused a bit of a scandal by classifying clasia based on the female abilities to produce milk from their nipples cuz apparently that was pretty racy stuff back then in his lifetime L has cataloged roughly 7,700 plants and 4,400 animals he published his classifications in a catalog called cstem nure which by the time he wrote its 12th edition was 2,300 pages long in the meantime lenaeus actually adopted a personal motto God created lenaeus organized although taxonomy has come a long way since lus we still use a bunch of the conventions that he invented for instance we still arrange things into taxa or groups of organisms and we still use the same taxa as lenaeus Kingdom film class order family genus and species we also still use lenaeus as Convention of bomal nomenclature using a unique two-part name for every species the genus and its species name in Latin or sort of Latin is this practice actually started back in the Middle Ages when educated people were expected to know Latin we know a lot less Latin now but we know know a lot more about Evolution which lenaeus didn't and we have Technologies like genetic testing to classify relationships between organisms and yet we still use Lena's morphology based system because genetic evidence generally agrees with classifications that are made based on structure and form however because there was a lot of life that lenaeus had no idea about we had to stick a new taxa above Lena's Kingdom we call it domain and it's as broad as you can get the domains are bacteria archa and ukaria the bacteria and the ARA are procaryotes meaning that their genetic material goes Commando with no nucleus to enclose it while the ukaria make up all of the life forms with a nucleus and include pretty much all of the life that you think of is life and quite a lot of the life that you don't think about at all it might seem like since all macroscopic life only gets one domain it's kind of silly to give procaryotes to and for a long time we didn't we didn't divide them up into different domains they out together in a single domain called Monera but it later became clear that bacteria which live pretty much everywhere on Earth including inside of you when deep in the Earth's crust and ARA which are even more hearty than bacteria have distinct evolutionary histories ARA being more closely related to ukar and yes thus me and you they have totally different cell membranes and the enzymes that they use to make RNA their RNA polymerase is much more like ours under the domain ukaria which is by far the most interesting and even occasionally adorable domain we have kingdoms protista fungi Plante and Animalia now scientists have settled on these four for now but these are categories that are a human creation but there are good reasons for that human creation the unscientific truth is that we looked at life and divided it up based on what we saw so we were like well protests are single celled organisms so they're very different from the rest of the domain and plants get their energy from the Sun and fungi look and act very different from plants and animals and you know we already know know what animals are so they have to get their own kingdom and those scientists are sometimes loath to admit at that system of just looking and dividing things up actually worked pretty well for us not perfectly but pretty well but there's a reason why this worked so well evolutionarily there are actual categories each of these kingdoms is a huge branch in the tree of life at each branch an evolutionary change occurred that was so massively helpful that it spawned a vast diversity of descendants plants or Plante are the auto trops of the domain ukaria autot tropes meaning that they can feed themselves through photosynthesis of course they cellulose-based cell walls and chloroplast giving them a distinct difference from all other multicellular life there are two other sorts of trops there's the heterotrophs which get their energy by eating other organisms and the chemotrophs which are weird and crazy and only show up in bacteria and archa and they get their energy from chemicals now the Kingdom Protista is weird because it contains both autot tropes and heterotrophs some protests can synthesize While others eat living things protests are basically a bunch of weird eukaryotic single- celled organisms that may or may not be evolutionarily related to each other scientists are still trying to figure it out some are plant-like like algae some are more animall likee like amibas and some are fungus-like like slime molds proests are one of those gray areas I was telling you about so don't be surprised if by the time you're teaching this to your biology students there are more than four Kingdoms in ukaria fungi which are you know the funguses they include mushrooms and smuts and puffballs and Truffles and molds and yeasts and they're pretty cool because they have cell walls like plants but instead of being made of cellulose they're made of another carbohydrate called kiten which is also what the beak of a giant squid is made of or the exoskeleton of a beetle because fungi are heterotrophs like animals they have these sort of digestive enzymes that break down their food and get reabsorbed but they can't move so they don't require a stomach for digestion they just grow on top of whatever it is they're digesting and digest it right where it is which is super convenient and finally we have kingdom Animalia which is the lovely Kingdom that we find ourselves and 100% of adorable organisms in animals are multicellular always we are heterotrophic so we spend a lot of time hunting down food because we can't make it ourselves and almost all of us can move at least during some stage of our life cycle and most of us develop either two or three germ layers during embryonic development wait for it unless you're a sponge so like I said we use this taxonomic system to describe the common ancestry and evolutionary history of an organism looking at the philogenetic tree you can tell that humans are more closely related to mice than we are to fish and more closely related to fish than we are to fruit flies so how about we pick an organism and we follow it all the way through the taxa from Kingdom to species just to see how it works I know let's pick this Kitty cuz I know she'd like it right cat so kitties have cells that have nuclei and membr brain surrounded organel and they're multicellular and heterotrophic and have three germ layers of cells when they're embryos so they're in the kingdom anomalia and they have a spinal cord running down their backs protected by vertebra and discs in between them and they have a tail that doesn't have a butthole at the end of it like a worm which I'm really glad about and that puts her in the philm Cordata Kitty clearly does not like this so I'm going to put her down now and the Kitty lactates uh it gives birth to young like a cow instead of laying eggs like a chicken and they have fur and three special tiny bones in their ears that only mammals have so they're in the class mamia so she's more closely related to cow than to chicken good to know and like a bunch of other placental mammals that eat meat like weasels the mustelids and dogs the canines kitties are in the order Carnivora and they're in the cat family Fela whose members have lithe bodies and roundish heads and except for cheetah's retractable Claws and they're little than and tigers and Panthers which puts them in the genus felis and then at the level of the species the descriptions get pretty dang detailed so let's just say that you know what a cat is so the species name is ctis and look at that felis ctis no gy I could have that whole thing Coss stitched onto a pillow for you to sleep on no we go thank you for watching our Taxidermy ISS no I mean taxonomy episode of Crash Course biology we hope that you learned something thanks to everybody who helped put this episode together if you have any question questions for us please leave them on Facebook or Twitter in the comments below and we will get to them hopefully very quickly and we'll see you next time