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Main content
Current time:0:00Total duration:13:29

Natural selection and the owl butterfly

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.E (LO)
,
EVO‑1.E.1 (EK)
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EVO‑1.E.2 (EK)
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EVO‑1.E.3 (EK)
NGSS.HS:
HS‑LS4‑2
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HS‑LS4‑3
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HS‑LS4.B.1
,
HS‑LS4.B.2

Video transcript

in the first video on devolution I gave the example of the peppered moth during the industrial revolution in England and how before the Industrial Revolution there was a bunch of moths some were dark somewhere light somewhere in between but then once everything became soot filled all of a sudden the dark moths were less likely to be caught by predators and so all of the white moths got were less likely to be able to reproduce successfully so the black moth trait or that variant dominated and then if you came a little bit later and you saw the black moor all the moths have turned black it's like oh these moths are geniuses they appear to have somehow engineered their way to stay camouflaged and and and the point I was making there is that look that wasn't engineered or an explicit move but on the part of the moths or the DNA that that was just a natural byproduct of them having some variation and some of that variation was selected for so with that example that was pretty simple black or white but what about more complicated things so for example here here I have a couple of pictures what's commonly called the owl butterfly and what's amazing here and it's pretty obvious if I probably don't have to point out to you is it it looks like it's it's it's its wing looks like half of an owl's eye I mean I can almost you know draw a beak here you know and draw another wing there and you can imagine an owl staring at us right and here too I could imagine a beak here and you would think an owl on there too and so the question is how does something this good show up randomly right I mean you could imagine okay little spots or black and white or gray but how does something that looks so much like an i generate randomly now the answer is well there's a couple of answers one is why does this exist or this this I like pattern or this owl like eyes pattern and they're the the jury's still out on that idler I read a little bit of it about it on Wikipedia and these are all of these images I got from Wikipedia and Wikipedia they said look there's two there's two competing theories here one theory is that this you know in the this is even though to us humans the way we see things it looks like an owl's eye that this is actually a decoy that this is you know when some predator is about to chase is about to chase these these wants to eat one of these things they kind of go for the thing that looks most substantive so instead of going for the the butterfly's body which is you know it doesn't look that substantive they go for the big black thing they say oh that looks like it's protein rich and it'll be a good meal so they try to snap and bite at that and if they bite at that sure the guy's wings are going to be clipped a little bit and it's going to suck but the but the animal itself the the the actual butterfly would survive and maybe you know it can it can repair its wings I don't know the actual biology of the owl butterfly that's one theory and then the argument against that goes well know if that was the case and you would want the black spot even further back along its you know you'd want the spot way far away from the body you'd want it back here instead of right here because there's still a chance if something chomps it this little black spot that it'll still get the abdomen of the butterfly now the most the other theory as to why this exists and you know who knows maybe it's a little bit of both maybe both of these are true maybe this offers two advantages the other theory and this is kind of the one that jumps out at us when we see this hey this looks like an owl maybe this is to scare away the things that would are likely to eat this dude so maybe if and it does turns out in my reading that it they are lizards that like to eat these type of butterflies and those lizards probably don't like to be around Birds or owls because those owls eat them so that might be deterrent and then the other example they said is look they tend to be eaten by this lizard right here this is what Wikipedia told me and that this lizard tends to be eaten by this frog right there and that the eyes of this butterfly are not too dissimilar to the eyes of this frog and you know we can debate whether or not that's the case and if if this was the predator we're trying to mimic you could make an argument that maybe we would have had more green on our wing but that's not the point of this video and but it's a fun discussion to have as to what is useful about the side but let's have the question why how did that eye come about I want to say that I I mean the pattern on that wing what what set of events allow this to happen because when I described evolution and we know that everything in our biological Kingdom is just a set of proteins and then stuff that may be the protein cap but mainly protein and that proteins all coded for by DNA I'm going to do future videos on DNA but DNA is just a sequence of base pairs it's a sequence of these molecules and we represent the you know adenine and guanine and then cytosine and thymine and remember you have a couple of adenine x' in a row and some guanine and thymine and I'll do a lot more on this in the future but the idea is it's look it's just coded for by this sequence of these molecules how do you get a sequence you know how do you go from a butterfly that has no eye to all of a sudden I that goes there obviously just one change that happens from a random mutation may be that G turns into an A or that or maybe this C and this T get deleted so everything that alone isn't going to develop this beautiful of a pattern or this this useful of a pattern so how does how do the random changes explain something that that's this intricate and this is my explanation and obviously you know I wasn't sitting there watching over the thousands or millions of years as these owl butterflies emerge so this is just my theory of how natural selection does explain this type of phenomenon you have a world where you have in some environment you have butterflies and their wings look like you know let's say you have some butterflies that are generally like this that's their wing and it's a very bad drawing but I think you get the idea and there's just some general patterns we've seen it before there's variation and the variation does show up from these little random changes in DNA I think we can all believe that that most of these changes are kind of benign maybe they just set up differently where a little pattern will show up or a little speck of of pigment will show up with a slightly different color and we even see amongst these owl butterflies there is variation this dude's wing is different than that guy's wing what the commonality that they do have these eye looking shapes and there's not just one there's actually multiple this guy has this other thing up here that looks interesting and they have multiple things but the one really noticeable feature is this eye looking thing so how do we go from this to an eye looking thing so the idea is you have some variation one guy might look like that another guy or gal my register and 'm there dot might might be something like that another gal or guy these wings are really badly drawn but you get the idea that this is the butterfly says antenna right there that's its body another another person's patterns might or butterfly's patterns might look like this right and so they're just random but when they go into a certain environment for whatever reason maybe one of its predators maybe that theory that these are supposed to look like eyes is true and so actually maybe maybe this guy just has a random pattern here so maybe for this and so this guy and I'm not saying that one it's like definitely better that they're both going to be found and killed by predators but just it's all probabilistic right maybe this guy has a 1% chance less chance of getting a predator because when you predator just looks at them out of the corner of that eye that little really hazy region kind of looks like an eye and a predator would be better off just not messing with it and they'd rather go after the dude that looks like this so it's just a slight probability now you might say ok what's 1% going to do but when you compound that 1% over thousands and thousands of generations all of a sudden this trait might dominate and because he's just going to be killed that less frequently 1% less frequently now maybe this guy has a similar trait but his spot is closer to the abdomen and here it's a trade-off because maybe some predators get scared away by this concentration of pigment and once again this is not I'm not saying that we're here yet we're not at this kind of very advanced sophisticated pattern yet where this just this random concentration of pigment that just shows up so we see that people who have this concentration of pigment further away from their abdomen they do well but when it's too close maybe some predators think that that's actually an insect and they want to eat it so that's actually a bad that's actually a bad trait so what happens is this guy dominates and so within this population you start having a lot of variation because he starts representing them this he's more likely to pass on these traits and I want to make that clear that point very clear this isn't what happens over the course of an animal's lifetime it's not like if somehow I experience something or at least our current theory if I experience something that I can somehow pass on that knowledge to my child what it says is if I experience some if my DNA just happens to just some variation that happens to be more useful or more likely for me to survive to reproduction and for my children to survive then that will start to dominate in the population so then the population you're going to have variations within that maybe some guys you know it's going to get a little bit look like that maybe another one's going to look a little bit like that maybe some spots there you can kind of view it as the variation is quote-unquote exploring but I want to be very clear not to use any active verbs here because this is all being done really as a as a almost a common-sense process where everything changes the changes that are most suited are the ones that are going to survive more frequently and then the next generation is going to have more of that and then you'll you'll have variation within that change and then this one might be like that and maybe this is the one you know these were you good compared to that but now when you're competing amongst themselves this one is able to reproduce 1% more then this guy or this guy and then you can so this guy becomes and maybe it's some combination of all the well and they mix and match it's a hugely complex system but then this guy represents most of the population and when I say this guy I'm saying this guy's genetic information at least as which pertains to his wings and then you get variation amongst that maybe some of it they have a little small dot and there's some dots around it maybe it's like this may be one of them digresses and goes back here but then he has trouble competing so he gets knocked out again and then some other people haven't that back here I think you get the point that this isn't happening overnight it's hope it happening just these changes can be fairly incremental but we're doing it over thousands of generations so when you're talking about thousands of generations or even millions of generations even a 1% advantage can be significant and when you accumulate those variations over a large period of time you can get to fairly intricate patterns like this so I just wanted to explain that because that you know this is often used as a you know how does sure I can believe the butterfly moth or I could even maybe believe the examples of the antibiotics and the bacteria or the flu and because those are kind of real-time examples but how does something this intricate show up and actually want to make a point here we think this is more intricate because we can relate to it in our everyday lives but if you actually look at the structure of a bacteria and how it operates or what a virus does to infiltrate an immune system or a cell that's actually on a lot more levels a lot more intricate than a design in fact the whole reason why I'm using this as an example is because this is a fairly simple example as opposed to kind of explaining the metabolism of a certain type of bacteria and how that might change and how it might become immune to penicillin or whatever else but I want to make this very clear that these very intricate things they don't happen overnight it's not like one butterfly was you know all of us was you know completely looked like one uniform hot pink color and then all of a sudden they have a child who whose wings looked just like this no it happens over large periods of time although there might be some little weird hormonal change that does this but I'm not going to go go there but that is possible but I just want to make this point because I think the more examples we see the more it'll kind of hit home that this is a passive process we're not talking about these things happening overnight and it's actually really it's really interesting to kind of look at our world around us and look at ecosystems as they are today and try to think really hard about how something came to be what it's useful for why it might have been selected for for example I'll leave you know our things are traits that occur after reproduction selected for well probably not unless they affect the reproduction of the next cycle for example it is you might say oh well the trait to be nurturing after your reproductive a years that say you know that's after reproductive years nobody it helps your your offspring reproduce but you know we already see a lot of diseases especially once we get beyond our reproductive and our child-rearing years so once we get into our 50s and 60s the incidences of diseases it increases exponentially from when we were younger and that's because they're no longer being selected for because it no longer affects our ability to reproduce because we've already reproduced we've already raised our children so that they could reproduce so anything that happens that point is now not being selected for so anyway hopefully this video gave you a little bit more nuance on evolution and I want to do a couple of videos like this because I really want to make it clear that it's not making some wild you know claim that all of a sudden this appear spontaneously that it really is a thing that happens over millennia and eons and very gradually
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