Taxonomy, Phylogeny and Systematics

hi everybody today we're going to take a look at how we classify living things and nowadays that is done through what we call systematics and phylogeny so what we're going to do first is we're going to take a look at why there's a need to classify living things and then how systematics and phylogeny play their part so let's take a look at a simple example so upon first glance one would probably classify this as a and there's no doubt in my mind a word is probably jumping into your head right now as was the first time that I saw it but I'm upon closer inspection we find that it isn't actually a snake instead it is a different species altogether so let's look at some of the things that make this animal not a snake first there's no fused eyelid second no short terior posterior to the anus and third no highly mobile jaw those three things are key attributes of snakes and this doesn't have them so this is actually what we call a legless lizard at one time long ago it did have legs but over time developmental changes in evolution have changed this organism so it no longer needs them but it's still successful in the environments that it lives in so then we are interested in organizing life correctly we don't want to make mistakes seeing what an organism looks like one thing so it must be that thing and the branch of biology concerned with identifying naming and classifying organisms of course is taxonomy chances are early in your biology class you cover this but let's give it a go one more time so what we have here is we have a gray wolf and what we're going to do is we're going to go through the various levels of taxa and hopefully we remember the different names from top to bottom of how to classify this thing now what I do is I like to think of a quick little reminder statement and it goes something like this in my head I say dumb kids playing chess on freeways get squished and that's usually enough for me to remember so I can hit all the levels from top to bottom so of course with D my darn I have domain next is Kingdom and if you remember we've kind of messed around with the whole five Kingdom thing and it's no longer in play we took away the Kingdom ship of the protis because we found with newly discovered DNA and RNA sequences they're actually closer to the plants and animals and fungi than they are to each other so next after Kingdom we have phylum whoops there we go i misspelled tit phylum next is class then we have order family there we go make a better elder genus and lastly species okay so we have a domain Eukarya kingdom Animalia phylum Chordata class Mammalia order carnivora family canada genus canis and species lupus that's a lot of things in the name but remember we are classifying this from the most specific thing which is the species all the way to the broadest term in this case is domain and we'll look at how each level is nested in the one above it in just a minute so actually let me throw that term at you right now when we say that a group is being nested it means that it exists in the level above it usually with multiple other groups as well so each one of these lower groups is nested in the one above it and I'll go ahead and I'll show you an example of how that works in the next slide so if you're having trouble with a nested idea I want you to think of your global address so think of your regular address that you write an envelope right now but you also have a global address and what we can do is we can start at the very large and we can work our way to the very small for example we all live on planet Earth and that is a pretty big place and so seven billion other people's that have their own address as well second uh we live in a certain hemisphere okay I happen to live in the Northern Hemisphere and the Western Hemisphere so I live in a couple of them as well as everybody else I live on the continent of North America I live in the country of the United States my state is Michigan my city I'm not going to give my city but my city is somewhere in Michigan and I live on a particular street and I have a particular address now of course a whole bunch of other people have addresses on my street as well and that allows my street address to be nested on the street that I live in and my street is one of many in my city and my city of course is one of very of many in my state and I can go on and on so each small thing is nested into a bigger level okay so each level of organization then taxa is plural and so each individual one is not a tax uh but it's a tax on and this particular breakdown and organization for this organism this is a parson a sis's King Kolya also known as the Virginia Creeper and you can see that so we can go through those same things darn kids playing chess on freeways get squished domain Eukarya Kingdom Plantae the phylum is antha fighta class eudicot Atilla Doan order vitaly's family buy tasty a genre is Parthenos Issus and then the species name kingka folia alright so a taxon then is a group of organisms that fills a particular category of classification and it depends on which one you're looking at so each one of these is an actual taxon so there's multiple levels of taxa plural as we try to classify a particular organism in the mid 18th century carolus linnaeus developed the binomial system of nomenclature to classify organisms so binomial nomenclature means a two-part name and those two parts are these the first word is going to be the genus the second word is the specific epithet this refers to one species of potentially many within the genus so we saw the gray wolf as being Canis lupus but there's a number of other specific epithets that sit under the heading genus of canis so lupus was just one for the gray wolf there's also a red wolf and there's plenty more but we don't have time for that right now okay so species will then be referred to by its full binomial name its genus and its species the genus name can be used alone to refer to a group of related species so if I'm talking about wolves I'm going to say canis the canis group because I'm covering all the different subtypes all the different species of wolves that exist so I want you to also think about the need for proper classification and I do that through a question that you see here what is unique about these fish so you see jellyfish crawfish and silverfish okay so what's unique about them well the answer may be surprising none of them are actually fish so a jellyfish is what we call a Nigerian crawfish and a silverfish are arthropods and ones I once an insect so the fact they all have fish as part of their common name doesn't do a whole lot of someone trying to classify out different organisms and also these are all three of these are listed by their common names so each one of these would be better served a head something more specific so let's zero in on crawfish just for a minute it's very popular American arthropod and if we go around region to region the United States we might find different ways of referring to a crawfish and here are some a crayfish a crawdad a freshwater lobster or a mud bug all right so those four things might lead to some I guess we could say some trouble if you're trying to explain to someone what some thing is so one person's crayfish might be another person's crawdad and freshwater Lobster and Mudbug so what we are looking for in biology is a more standard system of naming that allows us to zero in on exactly the species that we're talking about so there's a need for scientific names and those needs come from the fact that common names will vary locally and globally languages very often things are lost in translation and you know to have a system and play that everybody uses is going to allow us all to know exactly the type of species we're referring to so just like the metric system the metric system is based on the number of ten and it's very easy to convert from one unit to another in about 99% of the countries on planet earth use the metric system because that language of measuring things is so easy and so universal okay some important information coming your way when referring to a species or writing it down you should italicize both your genus and species you should capitalize the genus name however you're going to leave the species name as lowercase you can use a single capital letter with the species name if you mentioned it previously so what that means is if I've written a report on Canis lupus and I keep referring back to that species what I'm going to do in every uh every case in the future of the report from that point forward is I'm going to use the capital letter C which represents canis and then I'm going to use the lowercase for the rest of it and that's just going to cut down the writing and we know it's we're talking about Canis lupus if we see see lupus for the rest of the report um importantly whatever the organism is named you're going to know it's and notice it has a Latin ending and that's actually part of the rules of naming organisms so we have these rules out there however wherever there's rules of course scientists like to have a little bit of fun too so what they're going to do is they're going to come up with names for organisms as they're discovered and there is some freedom in that to which you'll see in a second so classification is going to list the unique characters of each taxon and its attended to reflect phylogeny so what's all this about well if you're going to put something in a group the chances are it's going to have some of the same physical attributes as the others in that group and it's intended to reflect this world word called phylogeny which is an evolutionary history of a particular organism but sometimes you're going to see this by the naming it's not always the case check this up so biologists we all have good sense of humor of course and we even utilize that as we name new species as we find them so here's just an example of a number of species that have very unique genus and species names so we have a little bit of fun with it but having fun with that and trying to put things together in groups it tends to get away from the serious and get into just naming stuff whatever it seems like there are rules though there are two governing organizations we have the international code of zoological nomenclature the iczn and the international code of botanical nomenclature for plants of icbn and here's what they say they say authors should exercise reasonable care and consideration in forming new names to ensure they are chosen with the subsequent users in mind that are as far as possible they are appropriate compact euphonious memorable and do not cause offence but you know that is not obviously the aim of biologists they're out there to you know show the rest of the world they're finding but something is lost there we lose a little bit of any connection to how that species came about when we just have the two-part name so there's a weakness with Linnaeus system and in fact if we can utilize another system which we'll talk about a little bit it might be a more valid way to explain why in organisms exist by the group that it's in because it shares a buttes from the past so as we try to figure out where organisms came from what's going to come into play is a type of way of thinking about that called systematics so systematics is going to lead us to what we call phylogeny the evolutionary history what's found in systematics well as you can see here we're going to use fossil record data to help us figure it out we're going to use comparative anatomy and development and also we're going to use molecular data to determine what those evolutionary relationships are so how do we go ahead and decipher evolutionary history well a goal of systematics is then to determine that phylogeny okay so phylogeny and evolutionary history we're basically talking about the same thing here okay one is just a much smarter sounding word than evolutionary history so Linnaeus system as I said before it provided little information about that phylogeny and we're going to visually show phylogeny through a phylogenetic tree a diagram indicating lines of descent now what those trees look like is what you see here each branching point that you see is a divergence from a common ancestor so this one here we have 1 2 3 4 5 different common ancestors and the first most recent common ancestor is going to give rise in this case to the bear and the chimpanzee now are there other species amongst the Bergen pansy from the common ancestor of course this is just two that it's showing but there are hundreds and thousands of species that also come from that common ancestor but if you track back past the common interests of a bear and a chimpanzee you then get to a for a four-legged animal that also gave rise to lizards lizards and probably the rest of the reptile family if we go further back than that we get into the amphibian group and we don't have this developed lungs we now have skin that aids in our respiration mucus coating we always have to stay in a kwatak or nearly aquatic environment it's always wet if we go further back than that we find the fish family and for the back net the lamprey family so in this we have a lot of common ancestors but you got to basically take steps back as you look at the groups that are involved and this particular comparison all right now each one of these branching points is also called a node so in here we have one two three four five different nodes as well so when constructing a tree we're going to use two types of characters in order to do so first we're gonna use common characters and that means that it's present in all members of the group and present in the common ancestor second we're going to use derived characters that are present in some members of a group but absent in the common ancestor those traits were not seen previously so what we could say is that the common characters might exist from this species to this branching point here and taxon a B and C all wound up with the same character but at some point these if you keep tracking back those common characters were not there and that would then make it a derived character so let's say at the at the most at the furthest back ancestor of all these species of a through F this one here this common ancestor does not have the same characteristics ABC has and instead that's the whole reason why it branch to the dog to the left here so it gains some new attribute here and it stayed with all of the species that wound up here now that attribute is what allowed this group here on the right to go this way instead because they did not share it whatsoever so de and F do not share whatever that attribute was that a B and C have so they still have the common character but they don't have in case if we use a color here this red character is that is derived so actually let me write that down so red equals derived but I we can also say that this group also um sorry this group here has the common characteristic there we go okay a couple other things that we can say is uh in this group to the right or bottom we also find what's called a poly Tomy and a poly Tomy is when you find a pitchfork like structure in your phylogenetic tree and we notice that multiple branches come off the same note if that occurs it means that there's a little bit of unknown information there we're not exactly sure how de and F came about and that's why we kind of have this perpendicular line crossing here at the node and multiple species coming off them whereas on the top part here we definitely have a left and a right kind of like an either-or kind of deal and then we have the same thing going on here so in that case there there's a lot more solid evidence as to why one species branched into two versus if you have a pitchfork with multiple prongs at the same node and then we're not exactly sure that's how they show it in a phylogenetic tree alright so here we have another one showing we have a whole bunch of different species here cat family weasel family dog family and what we can point out and this one here is that we have what's called sister taxa and if you look at the end of your phylogenetic tree where it breaks it down further and further and further to species you're going to notice that sometimes you're going to get two species that are really close together so in this case here we have a coyote and a wolf and their sister taxa so those two species share an immediate common ancestor right here and it also means that their DNA and RNA are probably very similar as well we could also take a look at where the root of all the species on your phylogenetic tree is for example the cats the weasel family the dogs they all wind up at the same common ancestor and this one happens to be a good deal back from out here on the right hand side in fact it's so we got it way over here at the carnivore node back here so all these guys here on the right these are all carnivore and the closest we can link them all together is way back here at carnivore status all right we can also say um that it is what we call the root species if we think of a tree we're all these things out here are the branches well the root is what anchors it down into the ground and that's the most common point where all the branches might meet or the trunk we could say but this is the root species it's the most common ancestor of all the species you see on here and surprising to many a lot of people don't know this but if you look at the Felidae family it takes a left right here whereas a weasel family that must still a day and the kanaday take a right so what that means in terms of genetics is that the weasel family is actually closer to our canines then the the cat species the Fila days they're further away a lot of people don't know that they also don't know that hyena is this dog like as they are actually closely more closely related to the felidae family than they are the kanaday family just FYI we can also talk about the weakness of phylogenetic trees unless there are specific dates at the bottom of the tree that will be helped be evidenced by archaeological digs and fossil records we don't always know what the absolute ages of the species are and where breaks occurred so what we could say then is that here we have a branch point where the coyote and the wolf diverged from each other here we have a branch point where the Badger diverged from the otter but unless there's fossil evidence that has been dated we can't be sure which one of these things here happened first so in these cases we know there was a break we know something happened but because the fossil record is incomplete or if someone hasn't done the proper testing yet we can't always be sure which one happened first so that is a weakness of a phylogenetic tree if it is undated also please communicate to others as you learn more biology that sister taxa does not mean that one species came from another so what I mean by that if we look and focus in on the canis latrans and Canis lupus the coyote and the wolf we know that they're very closely related their sister taxa but that doesn't mean that one came from the other one instead we track back and at some point speciation occurred this one went one way this one went the other way on a genetic basis and after some time they were no longer able to successfully interbreed with each other it doesn't mean that one came from another often you'll hear people come with the argument saying I didn't come from a chimpanzee or they didn't come from a gorilla or an ape and we all know that that didn't happen but we all do share a common ancestor we all just went our own a unique evolutionary path to where we are today so through the weakness of the Linnaeus system of binomial nomenclature and groupings some systematics now propose that classification be based solely on evolutionary relationships on the phylogeny only and that is new ideas called the Philo code so this is only going to name groups with a common ancestor and all of the descendants that it has so what that's going to do it's going to basically take those ranks back out so species are no longer than ranks like family order in class and instead is going to lump some unique groups together we already started doing it with the protists they lost their Kingdom ship and now because they're closer to fungi and animals and plants we are now going to start putting them in those groups and this owl right here is going to become part of the reptile group instead of saying it's staying in a unique bird group that's unrelated to reptiles so why should we study phylogeny who cares anyways well there's some important reasons if a major species is species decimated and we need to bring that species back what would we do so it might be a keystone species that provides thing for our survival so by knowing the closest relatives of the species that may provide a reservoir for genes law that are found in the lost species so one example we could use would be corn okay so corn is the number two crop in the United States and probably all over the world as well and it's so important because of its food capabilities and the thousands of other products that we make from corn so the scary part is that corn is a monoculture for the most part we have multiple species of corn but we really stick to a couple big ones and that's about it and what that means is if a virus is able to find the code for corn and do severe damage to it it could wipe out huge fields and and kilometers and miles upon miles of corn because they're all the same so if we know other species of corn that are related might have come before through its phylogeny we might be able to do some genetic engineering we do some transplanting of genetic info from one species to another and bring back the lost species so today's world is a monoculture kind of world when it comes to plants and we need to have some diversity amongst those plants so those viruses in those threats can't take out the whole lot of them at the same time another example that comes to mind is the anthrax post 9/11 attacks through using genetics and breaking down the genetic code of the anthrax spores that were found in the weaponized anthrax after 9/11 they were able to then trace it back into species and a location where that particular genetic unique combination of DNA material was found and eventually find a location where that weaponized anthrax was made so what kind of data allows us to infer phylogenetic information well one type of data is morphological and that's physical attributes of living things the second one is molecular so the one is phenotype the other one is going to be genotype do you remember your genetics chapter all right so in morphological we're going to focus in on the in this case and the bones of four limbs of mammals and here we have five different mammals and we can see one common characteristic between all of them actually about a little bit more than that because we have a scapula in each one of these mammals we have a three boned for limb so each one of these has a humerus a radius and ulna so that is a one common homology we see there we also see some form of wrist type structure and the carpals and the metacarpals and even the phalanges that we find at the end horse doesn't have phalanges but some of the other ones do but the key thing here is there is a similarity between all these species which is of course evidence that chances are we're pretty closely related if we have the exact same bone structure in terms of the types of bones that are there not exactly how they look but the fact that they all are there and if we look at other animals like we go to the insect world they don't have bones they don't have a three boned for limb nor do they have a scapula so we're very different from those but we are very close to mammals if you looked up mammal features you'd find that a lot of us share a lot of the same similar characteristics now on the other hand we have molecular data as well and that's the genes and the DNA sequences that we can find that it can also be homologous if they're descended from a common ancestor we'll get into that in a minute now take a look at these two animals for a second as far as how they look their morphological of phenotype their morphological appearance they look kind of similar now of course the coloration is different but they kind of do this same thing they both kind of dig around in the ground they're pretty flat short tails eyesight not very good hands that kind of look like flippers or diggers because they're both types of moles one is an Australian mole and the other one is a North American mole now as different as are as similar as these two look there's going to be some key differences because they do not share a very common ancestor in fact the most common ancestor you could get to would be a long time ago in Pangaea was still all together because once you strip away the outside look to this and you looked on the inside they look incredibly different so environmental selection factors one in North America one in Australia and ecological niches these have selected four attributes that allow these two little critters to look alike however genetically speaking they're very different from each other um if we take a look just focus in on the reproductive system the australian mole is a marsupial which means that it completes its development in a pouch whereas the north american mole is eutherian which means that it develops in a uterus so a reproductive system that's completely different from the other one is going to lead to more evidence these probably don't share a very common ancestor is probably somewhere way far back a long time ago and it's just those selective pressures of the different environments that they live that allow each one to be successful in its own way and pushed it to basically do the same thing to have the same ecological niche as one another here's another example in what we are talking about where we have analogous structures such as wings because wings allow flight of course and we're going to call these homo places because selective pressures have allowed all three of these types of wings to develop in order for that particular species to be more successful however they come from very different evolutionary past their fallout phylogeny z' are way different but um if you take a look at the insect wing for example we mentioned the boneless aspect to an insect it doesn't have bones but it can still fly so the fact that it can fly is not a homologous type of thing instead it's an analogous type of thing instead it it developed this over millions upon millions of years that it can be more successful if it could actually fly to get away from predators and to drive nutrition and to reproduce more successfully now if we take a look at the bat and the bird which are closer evolutionarily speaking we can take a look at this little mini tree over here and see what happened so birds kind of went their own way which you can see here they went to the right and then some kind of common ancestor here went the other direction so there were some kind of four-legged individual root species but you know that may have been more reptile-like than anything and those on those scales eventually wound up evolving into feathers which allowed it eventually to take up a flight type of response to having you know these converted scales on their skin and eventually powered flight became part of its arsenal for survival but on this if you take a left here from the reptile species instead that left these species the common ancestor crawling on the ground and you can see at this point here there was a mouse like species that branch from the common ancestor but something happened here to go to the left which allowed a little bit of webbing to exist underneath the forelimb into the body of this particular this particular animal so maybe you don't upon thousands of years this animal using those flaps of skin that developed over time glided from tree to tree and eventually through you know births and deaths and and ultimately you know random combinations of genes started moving its arms and obtaining the ability to fly after a while which allowed to get away from predators find more food etc etc so very unique in the case that these two species here each independently involve evolve their ability to fly one was flying after its reptile form the other stayed on the ground mice went one way staying on the ground but bats developing you know this webbed appearance between the bones of the forelimb allowed it to fly and still around today because uh it was a it was a trait that allowed it for more evolutionary fitness here is some molecular data that we kind of take apart and try to figure out what's going on here looks pretty complicated let's try to simplify a little bit okay so if this file on up phylogenetic tree is a representation of what we see above let's take a look and let's start with species a and B down here at the bottom now a and B if we go through the code it's kind of hard to follow but we can see that there's a lot of similar letters between a and B and if we look at three spots in particular at two four and seven these are going to be some bases that are going to differentiate them from the other species in this tree for example a and B are pretty far away from species C and D because they don't share any of those same nitrogenous bases at position two four or seven days versus T's aids vs. CS and C's vs. A's now if we take a look at species C and D at position number one they each have G's but nothing else really shares it C's for everything else so they kind of go their own direction up here and eventually diverged from one another at a later time now if we look at some other species here e F G and H which all seem to share the same part of this tree right in the center right here what is it that makes the four of these so much more alike well we can look at the fact they all share position three so they all have T's at this location species a and F and G and H they diverged though whereas species a and F have a zat the six location and species G and H have seized at the five location so we can see even by more by molecular data we can take a look at the differences in similarities amongst different species and kind of hypothesize together what the evolutionary relationship might be and what we're finding is more and more is that this DNA and RNA information is stream ly reliable as opposed to the fossil record and homologous structures and things like that there are all evidence but DNA and RNA seem to be our new emerging leader in the quality of evidence that allows to relate one species to another analogous scenarios may also exist in molecular data now if you take a look at these sequences down here you can see that in various spots you find matches si si so here's got C and T and here's a G but if you look at everything else everything else is absolutely different and what that means is that it's an analogous structure um but within the nucleus of a cell so in this case it's just coincidence it's coincident these letters happen to match we call it a molecular homo play C so um don't derive don't try to glean too much worthwhile evidence from that because you're not going to find as much most worthwhile data we'll look actually more like this where it's you know if you're looking at related speech is going to be very very similar look at some of the percentages that we share with other mammals and you'll be astounded by the percent that matches so cladistics is a fancy word for an approach to systematics it's based on common ancestry and we utilize the idea of a clade a clade includes ancestral species and all of its descendants so let's take a look at some examples here we have three different examples where we can differentiate what a clade is versus a group only a clade is going to be consist of what we call a monophyletic group it consists of all the ancestral species our sorry ittan consists of the ancestral species and all of its descendants so in this case here at our first example we can see that species a B and C which we're going to call group 1 all of them seem to come from this common ancestor right there so that makes this particular group we're focusing in on a clade second a paraphyletic group consists of the ancestral species and some but not all of its descendants so in this case here we can clearly see there's a common ancestor but what we have is we have a species that doesn't quite get in there this species G here doesn't make it into the group and that's what we're going to call it a paraphyletic group and not a clade third we're going to look at a polyphyletic group and that includes taxa with different ancestors so in this case here of the de f and G species they all have the common ancestor there they radiate out but species C has made it in there and it has a completely different common ancestor so then we would call it a PI polyphyletic group and not actually a clade when inferring evolutionary relationships it's useful to know in which clade a shared derived character first appeared so let's take a look at some of these characters we have a shared ancestral character and that exists here as a vertebral column for the species of lamprey through leopard you'll notice the Lancel it does not have that shared ancestral character it does not have a vertebral column it has a notochord but it doesn't have vertebral column we also see a shared derived character and in this case here after vertebral columns hinge jaws for walking legs amniotic egg we develop hair over time and the leopard has hair so this derived character means that something has now shown has evolved this new character that it wasn't seen before in common ancestors we also need to select an out group and out-group is a species from an evolutionary heritage that diverse before the lineage we are studying so what that means is that all of these that we're looking at here if we were focusing in on these they are called the in-group and you can see that there so these guys here on the end group that means we have an out group and in this case here out group is going to be the lancelet and let me take my little owl away here so you can see what we're talking about so here the lancelet does not have a vertebral column so it is on its own as the out group in some trees the length of a branch can reflect the number of genetic changes that have taken place in a particular DNA sequence in that lineage so in this case here you can see that some of the species don't have a whole lot of changes but some do so if we ask the question which species has gone to the most genetic change I hope you would say definitely not the Drosophila not the fly in fact it stayed relatively the same over time of course there's been changes but not anything compared to how many changes these have gone through and how many common ancestors so in this case the mouse and the human have gone through the absolute most genetic change of all the species here on this this phylogenetic tree this particular table up above is showing the percent differences between sequences and various species so human versus mushroom versus tulip and what we can see here is that the difference between a human and a mushroom is about 30 percent between sequences and a human in a tulip is about 40 percent a mushroom in a tulip have about a forty percent difference as well so one of the things that we got to look at is is this evidence fitting for a particular phylogeny for a group of species systematists can never be sure finding the best tree in a large set of data it's more helpful if there's small data that we can look at and break down like this as we try to tackle a bigger problem they narrow possibilities by applying the principles of maximum parsimony and maximum likelihood the principle of maximum likelihood states that given certain rules about how DNA changes over time a tree can be found that reflects the most likely sequence of evolutionary events so maximum likelihood is related to this thing that we know called Occam's razor Occam's razor said all things being equal the simplest answer is usually the correct one so there's a variety of different ways that we can kind of take a look at the evolutionary history of a number of different species but one way is going to be simpler than the other and be the most likely way that they diverged from each other maximum persimmony on the other hand assumes that the tree that requires the fewest evolutionary events whereas we could say appearances of shared derived characters is the most likely so between the two of these we can usually say the simplest tree is going to be the correct one and if we take a look at these two pictures down here we can see there is a common ancestor amongst the human the fungus in the plant and this would be tree number one and we could contrast that with tree number two and then try to figure out which one is more likely now species have the ability to change over time and most of the time there is a background rate to mutations and genetic change that is there it is evident and it's relatively equal among species so if we take a look at the this tree versus that tree we're going to find the one on the left this tree here is definitely more equal in time and changes over time than the one on the right the right shows that there was a divergence between fungi and then there was a common ancestor between a human in it and a plant where the plant changed rather rapidly over time the human changed the human changes were were slower and the fungus was even slower than that and then we have the one in the left tree number one where we had both the human and the fungus go their own separate ways from the plan and that was more evenly distributed over time so what that leads to is the idea the hypothesis that this is more likely than this here and DNA evidence will back that up so in conclusion remember that phylogenetic trees are hypotheses as new information is found these hypotheses can be supported or rejected the best hypothesis for phylogenetic trees fit the most data the morphological data the molecular data the fossil data and all of that data has allowed us to do even more hypothesizing for in fact if we took a look at this owl and we were able to trace it back in time we could then give some of these traits of the owl and apply them or infer that the dinosaurs probably had these traits first and because the owl is still around today the owl is harboring some of those same traits but of course because we don't have dinosaurs to look at and watch and study today we can only use this data that we have today from the molecules morphology in the fossils to imagine what those dinosaurs may have been like so I hope this helped open up your understanding to the need for taxonomy the way that we look at taxonomy and the way that we want to reflect taxonomy now in evolutionary history versus just a big pool of two-part names so keep on studying and I'll catch you next time bye

Channel: ProfAmann

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Id: NcMTz_4pSKU

Length: 45min 51sec (2751 seconds)

Published: Thu Apr 10 2014