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Main content
Current time:0:00Total duration:17:39

Introduction to evolution and natural selection

AP.BIO:
EVO‑1 (EU)
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EVO‑1.C (LO)
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EVO‑1.C.1 (EK)
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EVO‑1.D (LO)
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EVO‑1.D.1 (EK)
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EVO‑1.D.2 (EK)
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EVO‑1.E (LO)
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EVO‑1.E.1 (EK)
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EVO‑1.E.2 (EK)
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EVO‑1.E.3 (EK)
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SYI‑3 (EU)
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SYI‑3.D (LO)
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SYI‑3.D.1 (EK)
AP.ENVSCI:
ERT‑2 (EU)
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ERT‑2.H (LO)
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ERT‑2.H.1 (EK)
,
ERT‑2.H.2 (EK)
NGSS.HS:
HS‑LS4.B
,
HS‑LS4.C

Video transcript

I think what is probably the most misunderstood concept in all of science and as we all know is now turning into one of the most contentious concepts maybe not in science but in our popular culture and that's the idea of evolution evolution and whenever we hear this word I mean even if we don't hear it in the by Allah biological context we imagine that something is changing it is evolving and so when we when people use the word evolution in our everyday context they think of this notion of change that you know this is going to test my drawing ability but they you know you see a ape you know bunt over we've all seen this picture at the natural museum and he's you know walking hunched back like that and his heads bent down and I'm doing my best that's the ape maybe maybe he's also wearing a hat and then you know they show this picture where he slowly slowly becomes more and more upright and eventually you know he turns into some dude who's just walking on his way to work you know also just as happy and now he's walking completely upright and you know it's some kind of implication that walking upright is better than the not walking upright etc etc oh he doesn't have a tail anymore let me eliminate that this guy does have a tail let me do it in a appropriate width this guy has a tail so you're going to excuse my drawing skills but we've all seen this if you've ever gone to a Natural History Museum and you know they'll just make more and more upright Apes and eventually you get to human being it's this idea that the Apes somehow changed into a human being and and and I've seen this in multiple contexts even inside of biology classes and even the scientific community they'll say oh the ape evolved into the human or the ape evolved into you know the the pre-human the guy that almost stood upright you know the guy that was a little bit hunched back but you know so he looked a little bit like an ape and a little bit like a human and so on and so forth and I want to be very clear here even though this process did happen that you did have creatures that over time accumulated changes that maybe their ancestors might have looked more like this and eventually they looked more like this there was no there was no active process going all on called evolution it's not like the ape said gee I would I would like my kids to look more like this dude so somehow I'm going to get my DNA to to to to get enough changes to look more like this and it's like the DNA knew the DNA didn't say hey it is better to be walking than to be you know kind of hunched back like an ape and so therefore I am going to try to somehow spontaneously change into this dude that's not what evolution is it's not like you know some people imagine that you know maybe there were there's a tree there's a tree and and on that tree there's a bunch of good fruit at the top of the tree there's a bunch of good fruit at the top of the tree maybe they're apples and then maybe you know you have some type of cow like creature or maybe some type of horse like creature says gee I would like to get to those apples and then you know just because they want to get there maybe the next generate they keep trying to raise their neck and then you know after generation after generation their necks get longer and longer and eventually they turn into giraffes that is not what evolution is and that's not what it implies although sometimes that the the everyday notion of the word seems to make us think that way what evolution is and actually this is the word that I prefer to use it's natural selection natural selection let me write that word down natural selection and literally what it means is is that in any in any population of living organisms you're going to have some variation and this is a important keyword here variation just means look there's just some there's just some change are you if you if you look look at you know the kids in your school you'll see variation some people are tall some people are short some people have blond hair some people have black hair so on and so forth there's always variation and what natural selection is is this process that sometimes environmental factor will select for certain variation some variations might not matter at all but some variations matter a lot one example that's given in every biology book but it really is interesting is I believe they're called the peppered moth and this was you know in pre-industrial pre-industrial revolution England that these moths that you know some of the moths were let me see if I can draw a moth well I think you get the idea you know they've dead little let me draw a couple of them let me draw a few peppered moths a couple of peppered moths there let me draw on it one more so most peppered moths there was this just this variation some of them or I guess we could call them more pepper than others so some of them might look like this you know they had let me do other colors we do it white so it had spots like that some of them might looked more like that no clearly they had some black spots on them and then some of them might have been you know oh well you know just barely have any spots you just have this natural variation like you'd see in any population of animals you'll see some variation in colors now they were all happy probably for thousands of years just this natural variation it just it was a it was a non important trait for these peppered moths but then all of a sudden the Industrial Revolution happens in England and all the soot gets released from all of these all of these factories that are you know running these these steam engines powered by coal and so all of a sudden a lot of the things that once were grey or white for example maybe some tree trunks let me draw some tree trunks maybe there were some tree trunks that used to look like this you know maybe it looked like a maybe it kept the maybe some tree trunks used to look something like this and a peppered moth would be pretty okay you know maybe there's some tree trunks that were pretty dark but all of a sudden the industrial revolution happens everything gets covered with soot from the coal being burned and then all of a sudden all the trees look like this they're just completely pitch black or they're a lot darker than they were before now all of a sudden you've had a major major change these moths environment and you have to think what what is going to select for these moths well one thing that might get these moths or birds and their ability and the ability of the birds to see the moths so all of a sudden if the environment became a lot blacker than it was before you can guess what's going to happen the birds are going to see the birds are going to see this dude a lot easier than they're going to see this dude because this dude on a black background he's going to be a lot harder to see and it's not like the birds won't catch this guy they'll catch all of them but they're going to catch this guy a lot more frequently so you can imagine what happens if the birds start catching these guys before they can reproduce or maybe while they're reproducing what's going to happen this guy the darker dudes are going to reproduce a lot more often and all of a sudden you're going to have a lot more moths that look like this you're going to have a lot more of these dudes so what happened here was there any design or was there any active change by any of the moths did any of the the moths I mean it looks like a really smart thing to do to become black right your your surrounding became black and you ate a couple of generations of these moths and all of a sudden the moths are black and you might say wow those moths are geniuses they all somehow decided to evolve into black moths in order to hide from the birds more easily but that's not what happened you had a bunch of you had a lot of variation in your peppered moth population and what happened was is that when everything turned darker and darker these dudes right here and dudettes had a lot more had a lot less success in reproducing these guys just reproduced more and more and more and these guys got eaten up before they were able to reduce or maybe while they were reproducing so that they couldn't they couldn't produce as many offspring and then this trait just became dominant and then the peppered moth just became you can kind of view it as a as a black moth now you might say ok Sal you know that's that's one example I need more this is you know natural selection it's it's purported to apply to everything it explains why or it's it's a it purports to explain why we why we evolved from you know basic bacteria or maybe even self-replicating a which I will talk about more in the future you know I need more evidence of this I need to see it in real time and the best example of this is really the flu is really the flu and I'll do other videos in the future on what viruses are and how they replicate and viruses are actually fascinating because it's not even clear that they're alive they're literally just little buckets of of DNA and sometimes RNA which we'll learn is genetic information and they're just contained in these viral these little protein containers that are these neat geometrical shapes and that's all they are they really don't have you know they're not like regular living organisms that that you know actively that actively move and that actively have metabolisms and all that what they do is they take that little DNA and they inject it into other things that can process it and then they use that DNA to produce more viruses but anyway I was I could do we can do a whole series of videos on the on viruses but the flu is a virus and what happens every year is you have a a certain type of virus a certain type of virus and they have some variation and I'll just make the variation by I don't know how many dots they have how many dots they have and they in fact let's say it's a human flu they infect humans and slowly are our immune systems which we can make a whole set of videos on as well start to recognize the virus and are able to attack them before they can do a lot of damage so now you can imagine what happens if let's say that this is the current flu let me do all of them they all they all have these little two dots and that's how and we'll talk in the future what these dots are and how they can be recognized but let's say that's how our immune system recognize them they start realizing oh anytime I get this little green dude with two dots on it that's not a good thing to have around so I'm going to attack it in some way and destroy it before he infects my my mu my my DNA and all the rest and so you have a very strong natural selection once once the immune systems learn what this virus is and we'll talk more about what learning means for for an immune system that they'll start attacking these guys right they'll start attacking these guys but flu you can kind of think of them as being tricky but they're not really tricky they're not sent and objects but what they do do is they constantly change so what you have is in any flu population you're always having a little bit of change so maybe the great majority of them have those two dots but maybe every now and then one of them has one dot one of them has three dots and maybe that's just it's a random mutation this just randomly happened maybe one in every maybe this is one in every I'll make up a number one and every million of these viruses have this only one dot instead of two dots but what's going to happen as soon as say the human immune system gets used to attacking the virus with the two red dots well then this guy isn't going to have to compete with the other virus capsules for infecting people he's going to have people's DNA all to himself and so he or she or whatever you want to call this virus is then going to be more successful so by next tight year's flu season when people start sneezing and are able to spread it on doorknobs and whatever else again this guy is going to be the new flu virus so when you see this this process of every year there's a new flu virus that is that is evolution and natural selection in real time it is happening it isn't this thing that only happens out over eons and eons of time although most of kind of the the substantial things that we see in our lives or even ourselves are based on these things that happened over eons and eons of time but it happens on a yearly basis another example is if you think about antibiotics and bacteria bacteria these little cells that move around and we'll talk more about them you know they actually are definitely living they have metabolisms and whatever else and so when and this is just a nice know when people talk about infections it could either be a viral infection which are these things that go and infect your DNA and then use your cell mechanisms to reproduce or it could be a bacterial infection which are literally little cells that move around and they release toxins that make you sick and whatever else so bacteria these are what antibiotics kill anti anti biotics actually think there's a - anti biotics they attack bacteria they killed them now you probably if you know a couple of doctors or whatever and say hey I'm sick I think I have a bacterial infection give me some antibiotics responsible doctor says no you know I shouldn't I won't give you antibiotics just willy-nilly because what happens is is the more antibiotics you use you're more likely to create versions and and I want to be very careful about the word create because you're not actively creating them but let's say you and let me finish my sentence you're you're you're very likely to help select for antibiotic resistant bacteria is now how does that work so let's say a green let's say that this is let's say that these are all bacteria you have gazillions of them right and every now and then you get one that's slightly different all right you get one that's slightly different now in a random popular in a population of bacteria these are all will make you ramp equally sick and this is just some random difference in the bacteria may be on its DNA some slight different changes happened but whatever happened these all are you know the kind of bacteria you don't want to get a lot of them in your system your immune system can attack them and fight them off but if you get a lot of them and they might kill you or make you sick or whatever else now if everyone just starts using antibiotics when they're not sick is or when they don't really need to an alive for death situation is you might have an antibiotic that is really good at killing the green bacteria but what happens if you all of a sudden clean a lot of the kill a lot of the green bacteria well now the blue bacteria have the whole ecosystem that it was at before I was competing with all these green dudes to like you know get get at your at your get all the good stuff inside of your body but now he's all alone and now he can replicate willy-nilly so now he's going to replicate willy-nilly and obviously and this is once again he didn't it wasn't like there was any design that there was any intelligent process here that said look this bacteria should you know I'm just some bacteria said oh I'm going to be a little bit smarter and design myself to resist the to resist this you know this antibiotic threat no there's just these random changes that happen and mutations and viruses and bacteria happen frequently and the are these random changes that happened this might be a one in a you know in 1 billion change right but all of a sudden if you start killing off all of the people that it's competing with this guy can start replicating really fast and then become the dominant bacteria and then all of a sudden then all of a sudden that antibiotic that you you know that you had developed very carefully to destroy the green dudes is useless and you have this super bug you might have heard the word super bug that's what a super bug is it's not like it designed itself somehow it's just that we got very good at killing its competition and so we allowed it to take over and we can't kill it because all of the drugs were just good at killing its competition that these these bacteria just keep mutating and keep mutating and if we use these antibiotics a little bit too heavily will always be selecting for the things that won't be affected by the antibiotics well anyway I think I've spoken long enough but this is a fascinating fascinating topic and I really wanted to make this my very first my very first I guess video or lecture if you will on biology because if you really went to you know biology is the study of life and we can talk about what life is whether viruses are living whatnot but if you really want to study living systems you really can't make any assumptions other than natural selection we could go to another planet where the creatures don't have DNA or maybe they have some other type of hereditary information stored in their cells or they or they replicate some other way or they're not even carbon-based maybe there's silicon based and if we went to that type of a planet in order to tell you the biology on that planet everything else we know about biology about viruses and DNA would be useless but if we do understand this one concept this one concept of natural selection that your environment will select and it's not you know there's no active process here it's just random stuff happen and they randomly select for random changes and over large swathes of time and these are unimaginably large swathes of time those those changes essentially accumulate and they might accumulate it to fairly fairly significant things we'll talk more about this in another video see you soon
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