Evolution and natural selection
Introduction to Evolution and Natural Selection Introduction to evolution, variation in a population and natural selection
Introduction to Evolution and Natural Selection
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- 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 - may be not in science, but in our popular culture - is the idea of evolution.
- And whenever we hear this word - I mean: even if we don't hear in in the biological context -,
- we imagine that something is changing, it is evolving, and so when people use the word evolution in
- its 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 an ape, bent over, we've all seen this picture at the natural museum
- and he is walking hunchback like that, and his head's bent down, and
- - well, I'm doing my best - that's the ape, and may be is also wearing a hat
- and then they show this picture where he slowly slowly becomes more and more upright
- and eventually he turns into some dude who is just walking on his way to work, also just as happy.
- And now he is walking completely upright and - you know - there is some kind of implication that walking upright
- is better than not walking upright, and - oh he doesn't have a tail anymore.
- Let me eliminate that. This guy does have a tail.
- And let me do it in a appropriate width. You are gonna have to excuse my drawing skills.
- But we've all seen this, if you have ever gone to a natural history museum.
- They'll just make more and more upright apes and eventually you get to a human being.
- And there is this idea that the apes somehow changed into a human being.
- and I've seen this in multiple contexts and even inside of biology classes and even in the scientific community
- they'll say: oh the ape evolved into the human or the ape evolved into the pre-human:
- the guy that almost stood upright,
- you know, the guy that was a little bit hunched back, 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 active process going on, called evolution.
- It was not like the ape said: Gee, I would like my kids to look more like this dude.
- So somehow I'm gonna get my DNA to get enough changes to look more like this.
- It is not like the DNA knew.
- The DNA didn't say: Hey, it is better to be walking than to be kind of hunched back
- like an ape and you know therefore I'm going to try to somehow spontaneously change into this dude.
- That is not what evolution is.
- It is not like - you know - some people imagine that: Maybe there was a tree.
- There is a tree and on that tree there is a bunch of good fruit at the top of the tree.
- There is a bunch of good fruit at the top of the tree.
- Maybe they are apples. And then maybe, you know, you have some type of cow-like creature,
- or maybe it is some type of horse-like creature.
- It says: Gee, I would like to get to those apples.
- And that - you know - just because they want to get to those apples, may be the next generation....
- they keep trying to raise their neck, and then after generation after generation,
- their necks get longer and longer and eventually they turn into giraffes.
- That is not what evolution is and that is not what evolution implies,
- although sometimes 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 that in any population of living organisms you're going to have some variation.
- And this is an important key-word here. Variation just means: Look, there is just some change
- If you look at the kids in your school, you'll see variations.
- Some people are tall, some people are short, some people have blond hair, some people have black hair.
- So on and so forth. There is always variation.
- and what natural selection is, is this process
- that sometimes environmental factors will select for certain variations.
- Some variation might not matter at all, but some variations matter a lot.
- One example that is given in every biology book, but it really is interesting, is
- I believe they are called the peppered moth,
- and this was in pre-industrial revolution England,
- that these moths, that some of the moths were - let me see if I can draw a moth
- to give you the idea, you know, let me draw a couple of them,
- let me draw a few peppered moths.
- A couple of peppered moths there. Let me draw one more.
- So, most peppered moths there was just this variation, some of them were I guess
- we could call them more peppered than others.
- So, some of them might look like this, you know. No let me do another colour. Let's do white.
- So it has spots like that, some of them might have looked more like that.
- And of course they also had some black spots on them.
- And then some of them might have been, you know, almost - barely have any spots.
- You just have this natural variation like you would see in any population of animals.
- You'll see some variation in colours .
- Now they were all happy, probably for thousands of years, just this natural variation.
- Just this it was a non-important trait for these peppered moths
- but then all of a sudden the industrial revolution happens in England,
- and all of this soot gets released from all of these factories
- that are running these steam engines powered by coal, and so,
- all of a sudden all of these things that once were grey or white,
- for example maybe some tree trunks - let me draw some tree trunks -
- may there were some tree trunks that used to look like this, you know, may be it looked like a
- maybe it kept the, maybe some tree trunks looked something like this
- and a peppered moth would be pretty OK,
- maybe there were some tree trunks were pretty dark,
- but all of a sudden the industrial revolution happened,
- everything gets covered with soot from the coal being burned and then all of a sudden all
- the trees look like this:
- They are completely pitch black or they are a lot darker than they were before.
- Now all of a sudden you have had a major change to these moths' environment, and you have to think:
- What is going to select for these moths? Well, one thing that might get these moths are birds
- and the ability of these 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 is going to happen:
- The birds are gonna see this dude a lot easier than they are gonna see this dude,
- cause this dude on the black background is gonna be a lot harder to see.
- And it is not like the birds won't catch this guy,
- they'll catch all of them, but they're gonna 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 may be while they are 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 gonna have a lot more moths that look like this.
- You're gonna 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?
- It looks like a really smart thing to do, to become black.
- Your surroundings became black and you wait for a couple of generations of these moths
- and all of a sudden the moths are black and you say: Wow, these moths are geniuses.
- They all somehow decided to evolve into black moths in order to hide from the birds more easily.
- But that is not what happened.
- You had a bunch of them. You had a lot of variation in your peppered moth population
- and what happened was that when everything turned darker and darker,
- these dudes right here, and dudettes, 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 reproduce or may while they were reproducing
- so that they couldn't produce as many offspring and then this trait became dominant.
- and then the peppered moth became - you can kind of view it as a black moth.
- Now you might say: OK Sal, that is one example, but I need more.
- This is natural selection, this is purported to apply to everything,
- it purports to explain why we evolved from basic bacteria
- or maybe from self replicating RNA which I will talk about more in the future.
- You know, I need more evidence of this - you know - 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 actually are fascinating, because it is not actually clear that they are alive,
- they're literally just little buckets 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 are not like regular living organisms,
- that actively move and that actively have metabolisms and all that.
- What they do is they take that little DNA
- and then they inject it into other things that can process it
- and then they use that DNA to produce more viruses.
- But anyway, I could, we could do a whole series of videos on viruses,
- but the flu is a virus and what happens every year is that you have a certain type of virus
- a certain type of virus and they have some variation
- and I'll just make the variation by how many dots they have.
- how many dots the have and they, in fact, - let's say it is a human flu, they infect humans -
- and slowly our immune systems, which we could 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 this is the current flu,
- let me do all of them, they all have these little two dots
- and that's how and we'll talk in the future about what these dots are.
- and how they can be recognized, but let's say that's how our immune system recognizes them.
- they start realizing: O, any time I get this little green dude with 2 dots on it,
- that is not a good thing to have around.
- So I am going to attack it in some way and destroy it before he infects my immune system and DNA and all the rest.
- And so you have a very strong natural selection once immune systems learn what this virus is
- and we'll talk more about what learning means for an immune system.
- that they'll start attacking these guys, right?
- But flu , you can kind of think of them as being tricky,
- but they are not really tricky, they are not sentient objects.
- But what they do do: They constantly change.
- so what you have in any flu population, you're always having a little bit of change,
- so may be the great majority of them have those two dots, but may be every now and then
- one of them has one dot, one of them has 3 dots, and maybe that is just
- a random mutation, this just randomly happened, maybe one in every - I'll make up a number -
- one in every million of these viruses has this only one dot instead of two dots,
- but what's gonna happen as soon as the human immune system gets used to attacking
- the virus with the two red dots, well then this guy isn't gonna have to compete with the other virus
- capsules for infecting people he's going to have people's DNA all to himself.
- He or she or what ever you want to call this virus, is then going to be more successful
- so by next year's flu season
- when people start sneezing and are able to spread it on door knobs and whatever else again,
- This guy is going to be the new flu virus. So when you see this process of every year there
- is a new flu virus, that is evolution and natural selection in real time. It is happening!
- It isn't this thing that only happens over eons and eons of time. Although most of the substantial things
- that we see in our lives or even in 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 are these little cells that move around and we'll talk more about them,
- they are definitely living, they have metabolisms and whatever else.
- And so this is just a nice thing to 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 and they move around
- and they release toxins that make you sick and whatever else,
- so bacteria these are what antibiotics kill.
- Anti-biotics. Actually I don't think there is a hyphen: Antibiotics.
- They attack bacteria, they kill them.
- Now you've probaly, if you know a couple of doctors or whatever, and you say:
- Hey I am sick, I think I have bacterial infection, give me some antibiotics,
- a responsible doctor says: No I shouldn't give you antibiotics just willy nilly, because what happens
- is that the more antibiotics you use, you're more likely to create versions
- and I want to be very careful about the word create,
- because you are not actively creating them, but let's say
- - and let me finish my sentence -
- you are very likely to help select for antibiotic-resistant bacteria.
- Now how does that work? Now let's say this is a green
- let's say that these are all bacteria and you have bazillions of them, right?
- And every now and then, you get one that is slightly different.
- Now in a random population of bacteria these all will make you equally sick
- and this is just some random difference in the bacteria
- may be on his DNA some slightly different changes happened, but whatever happened,
- these all are the kind of bacteria that you don't want to get a lot of them in your system.
- Your immune system can attack them and fight them off.
- If you get a lot of them they might kill you or make you sick or whatever else.
- Now, if everyone just starts using antibiotics when they are not sick or when they don't really need to
- in a life or death situation, you might have an antibiotic that is really good at killing the green bacteria.
- But what happens if you all of a sudden kill a lot of the green bacteria?
- Well, now the blue bacteria have the whole ecosystem, that before it was competing
- with all these green dudes to get at your - get all the good stuff inside of your body, but now he is all
- alone and now he can replicate willy nilly, so now he is going to replicate willy nilly and obviously
- and this is - once again - it isn't like there was any design, there was any intelligent process here that said:
- Hey look, this bacteria should, - you know, I am some bacteria - said: I am going to be a little bit smarter
- and design myself to resist this antibiotic threat .
- No, there is just these random changes that happened and mutations in viruses and bacteria happen frequently.
- And there are these random changes that happen and this might be this one in a billion change, right?
- but all of a sudden if you start killing off all the people that it is competing with then this
- guy can start replicating really fast and then become the dominant bacteria and then all of a sudden
- that antibiotic that you had developed very carefully to destroy the green dudes is useless.
- And you have this superbug. You might have heard the word superbug. That is what a superbug is.
- It's not like it designed itself somehow. It is 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.
- And these bacteria just keep mutating and keep mutating
- and if we use these antibiotics a little bit too heavily,
- we will always be selecting for the things that won't be affected by the antibiotics.
- Anyway, I think I have spoken long enough, but it 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 and what not, 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 may be they have some other type of hereditary information stored in their cells
- or they replicate in some other way or
- they are not even carbon based, may be they are silicon based
- and if we went to that type of a planet in order to study the biology on that planet everything else we know
- about biology and 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 you know there is no active process here,
- it is just some random stuff happened and they randomly select for random changes
- and over large swats of time and these are unimaginably large swaths of time
- those changes essentially accumulate, and they might accumulate for fairly fairly significant things
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