welcome everybody this is a recording from section 8 which is has the topic why are there so many types of organisms with a focus on evolution and diversity so first of all uh what you want to do is take a look at those key themes we're kind of revisiting those from the beginning of the semester um as i go through them try to think of examples of those maybe that'll help you put that those concepts back into your mind ready for the exam so the first one is life depends on the flow of information the next one is life depends on interactions between and within systems the next one is structure and function then we're looking at energy flow and matter cycling and then finally we're looking at evolution which is looking at unity within diversity so that's our key theme that we're looking at tonight it's the one that links everything together all right so evolution as biology's unifying theme first of all we would start and look at these questions we're going to do this actually in class because i'd like to have a discussion about it i'm going to go ahead and pause and then forward through this so that way we can't see any of these particular topics right now okay so now after that slide um which we'll talk about in class of course i want to remind you or ask you rather who do you think was the first to propose evolutionary theory that is species change over time now if you are like most students and most people in general you think well of course it's darwin but shockingly darwin was not actually this concept has been around for a long time and we're going to see how it is that he contributed to it in such a significant fashion that links our concept of evolution with the name darwin forever so first of all there was a greek philosopher ann aximander around 2500 years ago who thought you know species change and i just want to remind you here notice that i've written this as spp when you write spp it's kind of like when you write something like pp like pages 123 through 127 for example let me try that again 123 through 127 so you can see that that is plural for it so we'd say this is the plural when you see it written as for example sp that means that we're talking about the singular in that case just like you would say for example you might say page 123 okay so here what we're talking about is species in the plural okay so when you see that species in the plural you'll see it spp so this an aximander remember his concept was that species change that they're not the same and then there's aristotle you've probably heard about aristotle right he's everywhere throughout science the ironic thing is the science that he usually came up with he was usually wrong um but what was amazing about aristotle is that he thought about some questions and really verbalized them in a way that people hadn't been doing before so one of the concepts that he had in mind was that species are fixed meaning they don't change then of course we have the judeo-christian culture who took up this concept that species are fixed um as a result of creation and that um from their important texts the the um the bible that you'd see that earth was um figured out to be about 6 000 years old now in the 1700s french naturalist buffalo um studied uh fossils and he realized you know i'm thinking that the earth is older than six thousand years and he looked at fossils thinking how are we getting these different fossils in organisms that don't have the same kinds of structures now and then there was lamarck very influential around the 1800s and again thought species changed um it's it seems like there are differences and um when we look at lamarck it turns out he has a lot of the qualities that um stick with us today so there's a couple of concepts that i'd like to show to you one of them is called the theory of use and disuse and another one is a theory of his which is called theory of inheritance of acquired characteristics now like i said a moment ago his concepts are really prevalent and they stick within the minds of even people nowadays you'll notice them in some kinds of statements where they use these terms a species wants or it needs or it learns how to do something to adapt to etc if you see any of these words that's a big hint it's lamarcian and what we know now is that lamarckian concepts in general don't seem to work in the way that we see in terms of evidence so be aware of that if you see those terms that's a hint that you're thinking like lamarck does or did i should say and how many people still do all right so what is it that lamarck actually was thinking what did he hypothesize so he figured if there was a change in an organism or in different species the change is made by what the organism wants or needs and so that's where here the concepts come back up that we were just talking about now these two theories one of them was theory of use and disuse so the idea here is that use it or lose it so some examples would be that well we notice that people aren't or other organisms are not necessarily using particular body parts like the human appendix or little toes and those are going to be gradually disappearing in future we won't be seeing them so eventually those people will be born without those parts or very reduced which we call vestigial means non-functioning and then if you think about it though does that really make sense um you know why would we still have an appendix why do we still have little toes if that's the case is it just not long enough so clearly there's a big mistake in here in the thinking about it it's not going to be lost because we don't use it if it's not doing any harm there wouldn't be any selection against it another concept is the theory of inheritance of acquired characteristics so this concept is uh well let me ask you this first of all how many of you have had a parent have a high school or college level science class like biology well if you've said yeah that's me i've had a parent that has had that then the question would be like why are you here that would be kind of nice if you could say well my parents had it that means that i'll have it too the concept is if an organism change in its life in order to adapt to its environment those changes are passed on to its offspring so if your parents learn something then you would automatically get it but be careful that could be negative too right so say for instance if you had a grandfather that lost his leg in the war guess what you'd be born without a leg in the second generation meaning your parents and then probably also within yours so we know that this doesn't make sense either now there are two perspectives on evolution i said that there were a lot of similarities between lamarck and darwin um you can see just by looking at um their the years they were alive that they overlap to a certain degree in terms of um you know their lifespan and so um darwin probably knew of lamarck and lamarck might have known about darwin and what he was doing as well because darwin you know worked on some of these concepts before lamarck's death so the similarities in their ideas um first of all life is changed gradually over time and is still changing that organisms are all related to each other and that life evolved from fewer simpler organisms to many more complex organisms okay so what are the differences we're going to have to see that there were a lot of them so kind of need to get some information in terms of darwin's prior knowledge so a couple of things about darwin um include that he included that he understood about the concept of artificial selection so you see all of these dogs here they're all the same species they're just different breeds and the way they arose is due to artificial selection so for example um the reason why you ended up getting these kinds of dogs is because say for example a person decided you know i've been having lots of rodents that are found within um you know my farm or my house i'd love to have you know a little animal take care of them for me because they're eating through my food or they're making holes in material or they're eating up the crops whatever the case may be and so um how do we take care of it so what they would do was take maybe a very small dog that had the propensity to want to go after rodents for example and mated that with another small dog so that hopefully their legs would be nice and short and then you'd pick other individuals that had um you know from those puppies you'd have shorter legged dogs mated with other shorter legged dogs so ultimately they would have really short little petite legs compared to you know their ancestors and so ultimately what we end up with is a dachshund dachshund is the german way of saying dachshund i think they say in english which is a wiener dog right those little guys so um that's where you get this concept from is that you know and this and this breed from is people selecting for those particular traits that they wanted means a roof or ceiling and then junt is a dog so they would let their little wiener dogs up in the roof or the ceiling where the rats and mice might want to find a little home and then let them have them so let them go so that's where you end up getting all these different breeds of dogs they were selected for certain characteristics or various traits that they were looking for do they want to have a large dog that could withstand the cold so that it could you know help people who have fallen in an avalanche for example or are they looking for a particular quality of dog in terms of its fierceness and fighting with other dogs and you know that kind of a thing so um next when we can see another example he would have known about so the example here could be what you see in terms of corn so corn did not originally look like it does now it actually um had a stalk and it had these kernels on it that have little kind of parts coming out that were not as appetizing and so people learned the value of eating these things but when they go to collect them some of the seeds would fall out of their hands and some would um would stay in their hands and then they could plant those that stayed on the little stock and so that kind of made it less liable just to shatter originally as they were going along and they planted on purpose these ones that they really wanted and so from there they would select various traits maybe to have less of those little pieces sticking out maybe to be a little sweeter or a little miss starchier and that would be by selecting the individuals and planting those that they wanted and then their offspring would be like them and ultimately you can see um you know what it is that we end up with is something as grand and large as a a kernel cob of corn so um kind of an amazing thing to see now another thing is you might have seen in some groceries in the stores now um within the last you know five years or so there's getting to be a little bit of variety in carrots especially around you know things thanksgiving time when you end up seeing these the reality is that's nothing really new the reason why we have orange carrots however is something that really has a bit of history to it so the history goes like this that you have these carrots of varying colors and the farmers that lived in the netherlands were trying to please or i could say perhaps be obsequious which will be frank kissing ass dare i say it of the the local um uh royalty and their royalties last name happened to be arana means orange and dutch and so they picked the orange carrots to please these royalty and so is basically by this obsequious behavior that the rest of us eat really most commonly orange carrots people have started to recognize the value of other uh kind of heirloom kind of species and and i should say really heirloom breeds is really what it comes down to um nowadays so people are starting to bring back the um the other carrots and you've probably seen this in tomatoes and other stuff too so it's a little bit of history that made us select specifically for orange carrots being the common ones so in addition to that um darwin would have um been an avid reader he read a lot of different kinds of topics and one of the topics that were really was really interesting to him was geology he was reading by a scientist named charles lyell and lyell was looking at the various rock layers and the various processes that would lead to the planet looking like it does for example he was looking at erosion water erosion wind erosion things like that and he would also look at the rock layers and then recognize that wow this rock layer has this kind of fossil in it this rock layer has this kind of fossil in it and then this rock layer has this kind of fossil in it so what that did was over time he started to recognize it really doesn't make sense that the earth was only 6 000 years old that there was something else going on to it so that's what um charles darwin would have read now in terms of darwin himself before all of this um he was born to a family of privilege on february 2012 1809 which happens to be the same day and year as president lincoln by the way to give context his father was a medical doctor and his mother was of a famous family who made a particular kind of english china the kind that you serve tea on called wedgwood china and as a son in a wealthy family he had considerable opportunity availed to him educationally so he attended edinburgh um edinburgh um university and where he was studying medicine and that was of course because his his father really wanted to do this um unfortunately he did not really like medicine that much probably due to the fact that at that time there was very little in the way of kind of anesthesiology so the kind of surgeries they were performing were usually on people who were still fairly aware of what was going on and so he was really uh upset by that and um kind of repulsed by that actually so he did the next thing that somebody of his um status should do and that would be to study theology and he did that at cambridge um so as he graduated as a 22 year old from cambridge he was kind of indifferent towards his career as a country clergyman but instead wanted to go out and see the tropics and so um he uh had a lot of interesting experiences as a young man during this time you know people didn't have the internet or tv or movies or things like that and so they would entertain themselves in different ways and one way that the wealthy would entertain themselves is to become kind of a you know natural little expert in their particular area say it would be on shelves or on kinds of birds or leaves or whatever and so they'd have vast collections of these and when they'd have get-togethers they would describe their collections so he enjoyed doing that very much and that brought him to be interested in looking at geology more and looking specifically at the tropics so um instead of moving on to becoming a clergyman where he was not exactly sure that's what he wanted to do he was invited on um on the voyage of the hms beagle as a geologist and a dining companion for the captain the the captain was a young aristocrat named robert fitzroy now at the time a captain would be um an educated person as well and maybe the people on the ship would be less so and so you'd have this kind of person that you could have as a confidante or talk to about the things that you might be reading and so that was kind of his job now it turned out that originally the voyage of the beagle was only supposed to be two years long and it turned out ultimately it turned out to be five years long so um and it was uh primarily to go to south america but of course it became something a lot more vast than that and you can see that the voyage that he took kind of really ended up taking him around the world so um and much of that time he did not really want to spend time in the ship that was for a couple reasons number one he was constantly seasick and then number two he found the captain really boring and so anytime that he could get off the ship he was very happy to do that so he had not really um signed on to the beagle as its official naturalist but eventually he assumed that role and kind of began to think of himself that way so you know he was supposed to be a geologist but ended up looking at a much broader perspective not only looking at geology but animals and plants and kind of a natural world in general so um he ended up spending much of his time and making a lot of great efforts in the southern part of south america and then of course as most people know in the galapagos islands which are located um you know west of of ecuador and so um it was at this time down in south america that he found some really amazing um troves of fossils so he his first kind of clue about evolution came not from the galapagos but really three years before in 1832 on a beach along uh the north coast at punto alta so when he was there he found this amazing amount of fossils um which included nine great megafauna some uh unique to the americas from some 12 000 years ago so this included um a rhino-like toxidon which um you know was rather large and kind of stout um and then he also uh discovered the fossils of giant ground sloths to kind of give you an idea this is the fossils and there would be i just drew in a little picture of a kind of a human sized version of how big we would be compared to this this giant sloth right and to get it with its musculature you can see it's quite a formidable organism he also saw an extinct horse um in terms of its fossils and a carapace that reminded him of a giant armadillo so this is the carapace that we're talking about um it was ironic because he had just eaten armadillo in um the argentinian pompous and um there uh he then he saw this glipton and was just you know this is very interesting um he also a month later came across another location near punta alta again at monte armoso and um there he unearthed you know roden-like mammals and an extinct form of camel-like organism so most of these fossils were crated up and then sent back to england mostly to the care of a friend of his john stevens henslow a botanist at cambridge that he got to know who could then disseminate them to various people of various experiences so he uh entrusted much of the most of the description and identification to richard owen uh who was an up-and-co up-and-coming authority um on extinct mammals so it wasn't really during the time um while he was out in the actual field that he had the answers it was a little bit later but he was coming up with all these ideas at the same time so um he of course went to the galapagos islands and there he observed various adaptations of um of organisms that had inhabited the environments and so um here being the galapagos just to kind of give you an idea about it it's very interesting because um when you look at the different islands uh they are all very different from each other they're you know even on um isabella which is the large um island there you know are there are places where it's very volcanic and then there are places where it's a lot drier you might have one area where it's rockier the other one that's sandier so each one of these had kind of their own unique kind of environment about them so what he noticed was that organisms he saw before like land iguanas he knew about those but for the first time he saw something like a marine iguana you know he had seen land iguanas in uh south america and now see something there like the marine form which he couldn't find in south america he also saw the galapagos tortoises which were these large tortoises um and you know notice that on each island there were some differences like for example um some of them have a very high uh what they call saddleback they can reach up high with their heads some of them have much lower ones so there was variation depending on which island that they were on in fact a lot of what he figured out from uh the galapagos islands that we attribute to other organisms he could have figured out from the tortoises and i think that was actually contributing to his knowledge at the time about this whole concept of what we know as evolution um he also saw flightless cormorants which is this kind of bird um but hormones that he was familiar with usually could fly and then he saw some of these ubiquitous you know uh sea lions you find them everywhere right um and uh he'd find those as well so he's getting this really interesting conglomeration of um of information in these all these different organisms so darwin was a highly intensive uh fieldman he was intensely curious and a really keen observer and he learned as he went he applied himself diligently and maturing quickly to assume and transcend really the roles of the ship's naturalists so um when he returned ultimately he was really a seasoned naturalist at the age of 27 and he really didn't see himself any longer as a country person but was committed to a life of science now one of the things that he brought back with him or send back during the time were these specimens of birds um he was having um them identified by an expert named gould and another you know expert for mammals named owen and the reptiles to a man named thomas bell so what he did was he went to the experts to make sure um with that and then he put all of his thoughts in order and followed out his suspicions so when he sent these birds back it was of interest because you know he looked at him and they all looked really different from each other um he would think oh well this one kind of reminds me of a warbler and this one's an oriole and this one's more of a a finch and um and whatever types and then the experts said you know what actually uh they're all finches which was really surprising um and especially when you notice that their beaks look very different which of course is very imp important in terms of how they feed and also very important to birds is their their song and so the songs wouldn't even be similar to each other so um what he's darwin started to notice was that the plants and the animals that lived in temperate regions of south america seem more closely related to species living in tropical regions in that continent than those species living in temperate regions of europe so that kind of put some clues together um now again he thought that there were all these different species um you know black bees gross beaks and so forth and he didn't realize it turns out there were 14 related species um their morphology their shape their form really didn't indicate that and so um it was kind of a conundrum at the time so um about a year and a half later after adding one crucial piece to his thinking the idea of excess reproduction and struggle for existence which was a topic that came from malthus which we'll talk about a little bit darwin hit upon his theory of natural selection where best adapted individuals of each population survive to leave offspring and the others do not now how is it this happen what how could he explain what was happening in the galapagos islands with it being just a small area and having 14 different species that didn't even you know that you didn't even think were all finches for example so um what he noticed and we can see nowadays about the galapagos islands is this really interesting concept this area of the world as you know is on the equator and it happens to be a particularly interesting area in terms of the way that storms wind water current and all that converge into one location and so um you know you have all of these sources that come into this spot in the galapagos island now what he also knew and we see nowadays that happens is that um when this when you have a storm for example sometimes unfortunate birds or flocks individuals or flocks thereof um can end up in the storm and they might be going to a particular location but they end up somewhere completely different this is something that we can see nowadays still like in super storm sandy that i talked about that hit the east coast of united states some time ago and specifically hit new york very hard the people in new york who are amateur ornithologists those are people who uh as a hobby like to look at birds um and they're kind of interesting lot they have a tendency to take pieces of paper with lists of birds on them and then as they see them and identify them they check them off this is called your life list and so what you do is then you keep a copy for yourself and so you can kind of have a list of all the birds that you've ever seen before and then you go to specific places to see other ones but then you also send that life list back to say the local conservatory or whatever for birds and so that way they have the data as well and so what you can see is you know what are the typical birds are found in the area and um and then you can see what has changed over time well there were amateur ornithologists who had um in new york seen birds that they would have never normally seen before during the the huge super storm for example they would see um an arctic turn which should be up in the arctic not in new york um or they would see tropical birds that have been mistakenly thrown off into new york city in you know the incorrect location so and this happens with other organisms too not just birds for example if you have um some lizards that happen to be on a branch and that branch happens to break off and end up in the ocean sometimes what will happen is that branch will end up somewhere else and then the lizard finally you know gets off and then now it's got a new home and it you know if there are enough of them perhaps a new population starts there so um with this understanding um darwin could look at this and say you know what seemed to be logical is that there was a particular kind of finch from the american mainland the south american mainland and um had blown over um to a location probably on isabel and um there that population survived but the particular location that they were at was vastly different than their own homeland so those that would survive there would happen to be well adapted to that by chance that particular environment whereas others that were not well adapted they would die and so the subsequent populations um you know the offspring from those would look like the group that survived and then that population you know sometime later might again be blown off into another location with another very different environment and that population would also change based on who happened to survive and produce offspring versus those who could not produce offspring because they didn't survive and you would see this action over and over again over a very long period of time with each environment being slightly different you have different organisms and the populations that you'd end up seeing would be quite different from each other so this is um called adaptive radiation another way of describing this is that you start off with a common ancestor from the south american mainland and then when you see um the different kinds of birds based on say the food that was available you'd end up having different kinds of populations end up being vastly different from each other another way of representing this as well is by looking at it as though if this were the common um ancestor you could see that you know those that were able to eat fruit because fruit was available would end up having um population-wise parrot-like bills or grasping bills for insect eaters and so forth so adaptive radiation is the evolution of many new species from a common ancestor and that was because that common ancestor was introduced to a new and diverse environment so darwin's perspective was this it's not really the wants or desires of animals um you know that has anything to do with this the desires of animals have nothing to do with how they evolve and the changes in an organism during its life do not affect the evolution with of the species um these are where the the ideas conflict with lamarckian views on how species change so um it was quite some time later um that he went back to starting to write in the information down he didn't really take up this topic with you know a lot of enthusiasm originally not because he wasn't excited by the topic but he kind of actually tried to avoid writing this down in any major way and um the reason being is that he was keenly aware that his wife was a very religious person and that some of the ideas that he was coming up with didn't really follow those religious concepts so in order to maintain you know his his relationship with his wife he just kind of put it on the on the back burner and pretty much left it for quite some time so what happened later on though is that um he was writing about barnacles and all kinds of interesting things and then later on he was told that another scientist named alfred wallace was in the process of discovering an interesting concept and it turned out to be the same idea and so the two were brought together they discussed what was going on there was a situation where it was decided that they would hold a conference together and then it was recognized who had come up with the con the concepts first and that this information should definitely be distributed and really um it should the kind of the association with it should go to darwin and so um basically after uh he had concealed his theory for about 20 years then um he started to realize that he needed to get this done and his wife was very supportive of him so um it this prompted an immediate and joint publication of both of their theories in 1858 and then um he had been writing this kind of concept that he thought would be this huge tome a series of books um but what he ended up doing was taking this big kind of book aside and completing a much more streamlined version of this which he ultimately published in 1859 um the name being the origin of species which was kind of an interesting thing because its actual name was on the origin of species by means of natural selection it was a success a sellout success immediately um but of course i became the talk of the town and and people also then um looked at this in a uh fairly critical manner and um where they were looking at it and saying what is darwin trying to say about humans that you know what's going on where you know and what is with the origin of species they read this to mean originally the origin of life which is not what the the book was about and that turned on a certain group of people um in the religious community that became very threatened by this concept and so there was a lot of caricature and concepts that came behind it and um unfortunately without completely understanding what he was referring to there became this um antagonism between uh these two groups the scientific and the religious community when there probably didn't need to be um so as it states here the actual title is the on the origin of species by means of natural selection it really isn't the origin of life that wasn't really his topic so in any case what was it about the original concept is dissent with modification that's probably the most important part of it um that was his phrase by evolution so it's kind of like this if we think about who would your uh descendants be if you have them so think of who that would be well those would probably be your children if you have them and who are your ancestors well that would be your parents and grandparents and all the people before that right now you know even within a family that there are differences between individuals that not the children are not all exactly like the parents and the parents are not all exactly like the grandparents and so forth so just like we can think about that instead of looking at the family level we can look at it at the species level and then say modern species kind of the offspring in the essentials um that have descended from common ancestral species have been modified so there's changes that happen and how this was explained was through a concept known as natural selection that was the mechanism that he proposed for natural for descent and modification so the concept of descent with modification now we can kind of see this picture in terms of how we look at this on a phylogenetic tree or cladogram remember this um where the juncture is that's the kind of common ancestor and then we would have characteristics that would be potentially new in this particular species or new in this species and so forth so that's descent with modification so natural selection what's the big idea well um this kind of came out over time where he had a lot of observations that led to an inference and that ultimately came to and contributed to what we know as the concept of natural selection so the idea here is that all species tend to produce excessive numbers of offspring this idea actually was the malthus idea that i was talking about thomas malthus so it's malthusian in a concept malthus was actually an economist who was interested in looking at human populations and what he noticed was that people tend to produce lots of babies and so darwin said well that happens with other species not only just humans right and then uh the other concept that was malthusian was that um you know if there are scarce resources which there often will be that'll result in competition and so there will be this quote unquote struggle for survival and reproduction well again darwin said not only in humans right this happens within people the resources they might be excuse me um competing for might include water or food or housing or land that kind of a thing um and then of course in humans it would be jobs or that as well which all relate to you know these other resources so those two ideas came together what he noticed was that uh darwin noticed that within every population there's variation and some of this variation is heritable of course that means it's inherited from your parents so he made this inference a trait must lead to differential reproduction and individuals with a favorable trait must survive and reproduce leaving more offspring than other members of the population presumably some of them that don't even produce at all so that was his kind of concept behind it the idea overall his conclusion about this was that individuals whose inherited traits are best suited to the local environment and are more likely to survive and reproduce than less fit individuals and this is where we get this concept of survival of the fittest now fitness often is misunderstood to mean you know giant muscles that's not what it means we're not looking at this as the scenario right what we're looking at is something completely different survival of the fittest really is describing um a number so for example if in our class we have somebody who has uh four children and another person that has three and several people that have two children one person has one child what we would say is that the person who has the most children is the most fit and the person who has three children would be the next most fit those people with two children would be the next fit the one person with one child would be the least or would be the next fifth and then everybody else who doesn't have children would be not fit at all so ironically it it doesn't mean that you can't become fit later on if you choose to have children but at this moment that's kind of the description so you would have a fitness of zero one two three four however many children you have so fitness is the ability to survive and then also reproduce offspring so you know you might be lucky in love like these mice are but if something happens that you know you're not going to survive then you might not be able to have offspring whereas if you happen to have the characteristics that allow you to survive and reproduce then you're considered fit like these mice are so a couple of quick questions what are phenotypes based on well remember when we talked about this within genetics they should be based on genotypes right that's one thing so the genotype will code for the phenotype like proteins like we've also talked about within uh looking at transcription and translation right that's how that happens but it's not only based on phenotype it's not only based on genotypes sometimes there are aspects of it that are related to the environment so for example flamingo color i don't know if you remember this when we did a long time ago looking at hypotheses we learned that flamingos we think of them as pink but the reason why they are pink is because their genotype allows for them to phenotypically turn pink when they have pink pigment in their food available which is funny because if you ever have gone to the zoo people know oh they've got the pink flamingos out everybody wants to see pink ones right that's kind of what's cool about them but they actually have that pink pigment from the food that they eat now normally they would eat a kind of shrimp that gets kind of stinky so instead of at the zoo they feed them a different kind of protein and then add the pink in there so that they can still see their pink colors when the mothers are in the situation where they're feeding the crop milk which basically means pre-digested food that they kind of regurgitate regurgitate to their babies um most of their food goes to their babies and so then they end up turning this kind of white color again and it'll take them some time to actually regain their pink color um probably about two years so um we know that it's based on phenotype and genotype so what determines which individuals survive the phenotype in a given environment so you know who happens to have a longer neck when the trees are tall and everything else is eaten underneath is probably going to do better they're going to survive more than those that have shorter necks it's not stretching it's those who happen to already be fairly tall and what we'll see is that there are changes in populations over time we'll talk about this scenario later on so individuals are selected when we say selected that might mean as they say selected for let me write that down here when you say selected for that means you get to live that's survival if you're selected against that means for whatever reason you end up dying okay so maybe you're eaten by something maybe you're not you know well adapted to that particular disease whatever the case may be so individuals are selected but it's populations that evolve and that's what we'll be talking about next time when we meet in class for our last week of class all right everybody thank you for joining me and i will see you at our next meeting have a good one