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So the way that the sugars are oriented, if you're going from top to bottom the way we're looking here, you're going from three prime to five prime. So on the right-hand side, you are, it's three prime, five prime. And so if you wanted to draw an arrow from five prime to three prime, you could look at it like that. And... | Antiparallel structure of DNA strands Biology Khan Academy (2).mp3 |
And so you could say these are parallel, but since they are essentially oriented in, they're pointing in different directions, even though they're actually parallel, we would call the structure of DNA anti-parallel. So this would be an anti-parallel structure of DNA. So these two strands, they're complementary, they're... | Antiparallel structure of DNA strands Biology Khan Academy (2).mp3 |
The thymine bonds with the adenine, the cytosine bonds with the guanine, or they are attracted to each other through these hydrogen bonds, but the two backbones, they're pointed in different directions. Now another interesting thing to think about, since we're talking about the molecular structure of DNA, is how do the... | Antiparallel structure of DNA strands Biology Khan Academy (2).mp3 |
And part of, what plays part of that role is the fact that these phosphate groups are negative. So you think these things that have outright negative charge, they're gonna try to get as far away from each other as possible, and then when they, you know, they just keep kind of orienting, getting far away from each other... | Antiparallel structure of DNA strands Biology Khan Academy (2).mp3 |
So all of these phosphate groups on either strand, they want to get away from each other, and then these things want to, these things want to get close to each other because of the hydrogen bonds, and so that's what helps form this actual ladder structure. So DNA, fascinating molecule. We could speak for days about it.... | Antiparallel structure of DNA strands Biology Khan Academy (2).mp3 |
And then I have the water molecules depicted by these blue circles. And then I have the solute inside of the solution, inside of the water solution, that we depict with these yellow circles. And I've clearly exaggerated the size of the water molecules and the solute particles relative to the size of the cell, but I did... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
Now we're going to assume that the cellular membrane, this phospholipid bilayer, is semipermeable, that it will allow water molecules to pass in and out. So a water molecule could go from the inside to the outside or from the outside to the inside. But we're gonna assume that it does not allow the passage of the solute... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
So that's why it's semipermeable, it's permeable to certain things, or we could say selectively permeable. Now, what do we think is going to happen? Well, the first thing that you might observe is we have a lower concentration of solute on the outside than we have on the inside. So at any given moment in time, you will... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
So at any given moment in time, you will have some water molecules moving in just the right direction to go from the outside to the inside, and you will also have some water molecules that might be in just the right place to go from the inside to the outside. But what's more likely to happen, and what's going to happen... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
If they happen to be, if this one happens to be moving in that direction, well, it's gonna make its way to the membrane and then maybe get through the membrane. While something, maybe this, if this water molecule was moving in this direction, well, gee, it's gonna be obstructed now. Maybe this is bouncing back and it's... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
So the water molecules on the inside are more obstructed. They're less likely to be able to fully interact with the membrane or move in the right direction. They're being obstructed by these solute particles. So even though you're gonna have water molecules going back and forth, in a given period of time, you have a hi... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
So even though you're gonna have water molecules going back and forth, in a given period of time, you have a higher probability of more going in than going out. And so you're going to have a net inflow, net inflow, inflow of H2O, of water molecules. Now, a situation like this, where we're talking about a cell and it's ... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
The membrane is not permeable to that solute. We call this type of situation, this type of solution that the cell is immersed in, we call this a hypotonic solution. Hypotonic, hypotonic solution. And any time we're talking about hypotonic, or as we'll see, isotonic and hypertonic, we're talking about relative, we're ta... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
And any time we're talking about hypotonic, or as we'll see, isotonic and hypertonic, we're talking about relative, we're talking about relative concentrations of solute that cannot get through some type of, that cannot get through some type of a membrane. And the word hypo, you might have seen it in other things, it's... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
And because of that, you're going to have osmosis, you're gonna have water molecules going from the inside, or you're gonna have water molecules going from the outside, I should say, to the inside. And that's actually going to put pressure on the cell. The cell itself might expand, or it could even, if there's enough p... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
So now let's go to the next scenario. In this scenario, we have roughly equal concentrations of solute on the outside and on the inside, at least I tried to draw them that way. So in this situation, the probability of a water molecule in a given period of time going from the outside to the inside, or from the inside to... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
And so you're not going to have any net inflow or net outflow, you're always gonna have water molecules going back and forth, but there's not gonna be any net inflow or outflow. And so in this situation, so let's see, let me write, no net, no net flow. And this type of solution, where you have the same concentration of... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
And the prefix iso, which refers to things that are the same, it has the same concentration of solute. And so you have no net inflow. So hypotonic solution, you have water molecules going into the cell, the cell expanding, kind of like a filling balloon. Isotonic solution, no net flow. And then of course, you can imagi... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
Isotonic solution, no net flow. And then of course, you can imagine in this last scenario, I have a higher concentration of solute on the outside than I have on the inside. And we can guess what's going to happen. So first, what would I call this? Well, I have more of something in the solution, so I would use the prefi... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
So first, what would I call this? Well, I have more of something in the solution, so I would use the prefix hyper. I have more of it, more, hypertonic. This is a hypertonic solution. And once again, the water molecule, the solute can't go across the membrane, but the water molecules can. And you're gonna have water mol... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
This is a hypertonic solution. And once again, the water molecule, the solute can't go across the membrane, but the water molecules can. And you're gonna have water molecules going from the outside, going from the outside to the inside and from the inside to the outside. But the probability that the ones going from the... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
But the probability that the ones going from the, the ones on the inside are gonna be less obstructed to go out than the ones on the outside to go in. And so you're going to have a net outflow. You have a higher probability of things going from the inside to the outside than you do from things going from the outside to... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
And so they're gonna be held back, I guess, in different ways. So in this situation, you're gonna have, you're gonna have the water escape the cell and the cell actually might shrivel up. The cell, since it's gonna lose that pressure from the water, the cell itself might shrivel up in some way. And you can actually see... | Hypotonic, isotonic, and hypertonic solutions (tonicity) Khan Academy.mp3 |
And it is part of E. coli's genome. And it is involved, and the lac right over here is referring to lactose. And so you can imagine that it codes for genes involved in the metabolism of lactose. And the word lactose might already be familiar to you. It is a sugar found in milk. Some of us, including myself, are lactose... | Lac operon.mp3 |
And the word lactose might already be familiar to you. It is a sugar found in milk. Some of us, including myself, are lactose intolerant. I have trouble digesting lactose. So I have mixed feelings regarding this. But in general, for a cell to make use of it, it needs to be able to absorb the lactose. It needs to be abl... | Lac operon.mp3 |
I have trouble digesting lactose. So I have mixed feelings regarding this. But in general, for a cell to make use of it, it needs to be able to absorb the lactose. It needs to be able to split it up into simpler sugars that it can actually use for fuel. And that is what the genes in the lac operon actually do code for.... | Lac operon.mp3 |
It needs to be able to split it up into simpler sugars that it can actually use for fuel. And that is what the genes in the lac operon actually do code for. So just as an example, the lacZ gene right over here, this codes for an enzyme that helps cleave the lactose into simpler sugars. The lacY gene codes for an enzyme... | Lac operon.mp3 |
The lacY gene codes for an enzyme that allows for the absorption of lactose through cellular membranes. LacA is a little bit more interesting and a little less understood, but the general idea here is all three of these are involved in the metabolism and the absorption of lactose. And it is an operon, so we have our pr... | Lac operon.mp3 |
And I've also drawn some other sites. I've drawn the operator right over here where you can imagine a repressor, and it is indeed the lac repressor could bind. And over here, this CAP site, or C-A-P site, CAP stands for catabolite activator protein. Catabolite, catabolite activator. Whoops. Acti, activator protein. Pro... | Lac operon.mp3 |
Catabolite, catabolite activator. Whoops. Acti, activator protein. Protein. And so this is, you can imagine, where a protein called the catabolite activator protein can bind and perhaps be an activator. So with that out of the way, let's think about different scenarios. Let's think about a scenario, let's think about a... | Lac operon.mp3 |
Protein. And so this is, you can imagine, where a protein called the catabolite activator protein can bind and perhaps be an activator. So with that out of the way, let's think about different scenarios. Let's think about a scenario, let's think about a scenario where the E. coli is an environment where there is no lac... | Lac operon.mp3 |
Let's think about a scenario, let's think about a scenario where the E. coli is an environment where there is no lactose. So what do you think should happen over here? And a lot of these things are very logical. If you just assume that a lot of biological organisms are quite stingy, they don't want to just waste resour... | Lac operon.mp3 |
If you just assume that a lot of biological organisms are quite stingy, they don't want to just waste resources. Well, if there's no lactose, well, why transcribe the genes that can be translated into enzymes for the metabolism of lactose? So if there's no lactose, you can almost view this as a default state right over... | Lac operon.mp3 |
You actually have the lac repressor protein being bound to the operator. So this is the lac repressor, lac repressor right over there. And so you won't be able to transcribe these things. The RNA polymerase, the RNA polymerase won't be able to get anything done. No transcription is going to occur. So no lactose, no tra... | Lac operon.mp3 |
The RNA polymerase, the RNA polymerase won't be able to get anything done. No transcription is going to occur. So no lactose, no transcription. Transcription, which makes a lot of sense. The bacteria, or the bacterium, singular, doesn't want to waste resources. So what do you think should happen if there is lactose? So... | Lac operon.mp3 |
Transcription, which makes a lot of sense. The bacteria, or the bacterium, singular, doesn't want to waste resources. So what do you think should happen if there is lactose? So I'll keep this up here so you can see it. So lactose present. Lactose, lactose present. Well, you can imagine, well, you don't want that repres... | Lac operon.mp3 |
So I'll keep this up here so you can see it. So lactose present. Lactose, lactose present. Well, you can imagine, well, you don't want that repressor around anymore, and that is indeed what happens, is that you have an isomer of lactose called allolactose. So if lactose is present, you're going to have also allolactose... | Lac operon.mp3 |
Well, you can imagine, well, you don't want that repressor around anymore, and that is indeed what happens, is that you have an isomer of lactose called allolactose. So if lactose is present, you're going to have also allolactose present right over here. And so that is allolactose, which can act as an inducer of transc... | Lac operon.mp3 |
And the way that it acts as an inducer is if it binds to the lac repressor, the lac repressor can no longer bind to the operator site. So when the allolactose is present, it will bind to the repressor, and then the repressor is going to leave the operator site. It's not going to be able to bind as well. And so let me d... | Lac operon.mp3 |
And so let me draw that. So in this case, the operator, sorry, the repressor, I should say. The operator is where the repressor binds. So this is the repressor right over here. You have some allolactose. Let me do that in white. You have some allolactose that has bound to it. | Lac operon.mp3 |
So this is the repressor right over here. You have some allolactose. Let me do that in white. You have some allolactose that has bound to it. And because of that, it's not going to bind to the operator. And since it's not bound to the operator, well, now the RNA polymerase can actually transcribe these genes. And that'... | Lac operon.mp3 |
You have some allolactose that has bound to it. And because of that, it's not going to bind to the operator. And since it's not bound to the operator, well, now the RNA polymerase can actually transcribe these genes. And that's valuable because by transcribing these genes, we are going to be able to metabolize this lac... | Lac operon.mp3 |
And that's valuable because by transcribing these genes, we are going to be able to metabolize this lactose. So lactose present, you have transcription. Transcription. Transcription occurs. Now that's a very high-level simple view of the lac operon, but there's more involved because there's other sugars, in particular ... | Lac operon.mp3 |
Transcription occurs. Now that's a very high-level simple view of the lac operon, but there's more involved because there's other sugars, in particular glucose, which is preferred by the cell. So, whoops, I'm moving the wrong part. There you go. So let's think about what will happen in the presence of glucose and not i... | Lac operon.mp3 |
There you go. So let's think about what will happen in the presence of glucose and not in the presence of glucose. So let me write here. So glucose, glucose, and no, and no glucose. Actually, let me do it. Let me do it. Well, let me, I'll do no glucose first. | Lac operon.mp3 |
So glucose, glucose, and no, and no glucose. Actually, let me do it. Let me do it. Well, let me, I'll do no glucose first. Let's say we have no glucose. And remember, glucose is preferred to lactose. Simpler sugar, if you have glucose around, why worry about the lactose? | Lac operon.mp3 |
Well, let me, I'll do no glucose first. Let's say we have no glucose. And remember, glucose is preferred to lactose. Simpler sugar, if you have glucose around, why worry about the lactose? And then here we have, we have glucose, we have glucose around. And we could talk about both of these, both of these situations in ... | Lac operon.mp3 |
Simpler sugar, if you have glucose around, why worry about the lactose? And then here we have, we have glucose, we have glucose around. And we could talk about both of these, both of these situations in the presence of lactose or not in the presence of lactose, but if we don't have, if we don't have any lactose around,... | Lac operon.mp3 |
So you can, and that's going to be whether or not we have glucose. So I'm gonna think about no glucose, but we do have lactose plus lactose. And in here you have glucose plus, glucose plus lactose. Well, the lactose part, if we have lactose around, then we're going to have the allolactose around. And we just covered th... | Lac operon.mp3 |
Well, the lactose part, if we have lactose around, then we're going to have the allolactose around. And we just covered this scenario. The allolactose binds, binds to the lac repressor, keeps the lac repressor from binding to the operator. And so you have, you have your RNA polymerase is able to actually perform the tr... | Lac operon.mp3 |
And so you have, you have your RNA polymerase is able to actually perform the transcription. But that's not it. If you, in a situation with no glucose, you actually are going to also involve the capside. You're going to have an activator that's going to make this happen even more. Because if you don't have glucose arou... | Lac operon.mp3 |
You're going to have an activator that's going to make this happen even more. Because if you don't have glucose around, man, you really need that lactose. And so what you have is something called, so let me draw this, the catabolite activator protein, right over here. The catabolite activator protein. And in the presen... | Lac operon.mp3 |
The catabolite activator protein. And in the presence of cyclic AMP, adenosine monophosphate, it's a derivative of ATP. And so this is that right over there. Cyclic AMP, you'll see that come up a lot in biology. So this is the catabolite activator protein. In the presence of CAMP, and we'll talk about how cyclic AMP re... | Lac operon.mp3 |
Cyclic AMP, you'll see that come up a lot in biology. So this is the catabolite activator protein. In the presence of CAMP, and we'll talk about how cyclic AMP relates to glucose in a second. In that presence, it is going to bind to this, the capside. And it is going to further activate the transcription. So in this si... | Lac operon.mp3 |
In that presence, it is going to bind to this, the capside. And it is going to further activate the transcription. So in this situation, no glucose plus lactose, you're gonna have even more transcription. So let me write this down. Lots of transcription. Lots of trans, transcription. Lots of transcription. | Lac operon.mp3 |
So let me write this down. Lots of transcription. Lots of trans, transcription. Lots of transcription. Now I know what you're probably asking. This is what I first asked myself when people told me about cyclic AMP. Well how does cyclic AMP relate to glucose? | Lac operon.mp3 |
Lots of transcription. Now I know what you're probably asking. This is what I first asked myself when people told me about cyclic AMP. Well how does cyclic AMP relate to glucose? Well I'm not gonna go into a huge amount of detail here. But what you need to know here, and it makes sense, is that if you have glucose, so ... | Lac operon.mp3 |
Well how does cyclic AMP relate to glucose? Well I'm not gonna go into a huge amount of detail here. But what you need to know here, and it makes sense, is that if you have glucose, so let me write it this way. If you have high glucose, high glucose, I'm having trouble writing. High glucose, then that's going to inhibi... | Lac operon.mp3 |
If you have high glucose, high glucose, I'm having trouble writing. High glucose, then that's going to inhibit the production of cyclic AMP. So low cyclic adenosine monophosphate. And if you have low glucose, or no glucose, it's like a tongue twister. If you have low glucose, well you're not going to inhibit the creati... | Lac operon.mp3 |
And if you have low glucose, or no glucose, it's like a tongue twister. If you have low glucose, well you're not going to inhibit the creation of cyclic AMP. And so you're going to have high cyclic AMP. So if you have no glucose, or low glucose, we are in this scenario right over here. You're going to have high, or hig... | Lac operon.mp3 |
So if you have no glucose, or low glucose, we are in this scenario right over here. You're going to have high, or higher concentrations of cyclic AMP, which can bind to the catabolite activator protein, which then acts as an activator to allow even more transcription of the lac operon. Which once again, why is that imp... | Lac operon.mp3 |
Well if there's no glucose or low glucose, you're really going to need that lactose. You really want to transcribe these genes as much as possible. Now what about the situation where there is glucose and lactose? Well once again, if there is lactose, then you're going to have allolactose, which is going to be able to b... | Lac operon.mp3 |
Well once again, if there is lactose, then you're going to have allolactose, which is going to be able to bind to the lac repressor. And by it binding to the lac repressor, the lac repressor is not going to be able to bind to the operator. And so you do have, once again, the RNA polymerase is going to be able to transc... | Lac operon.mp3 |
But because you have glucose present, because you have glucose present, you're going to have low, or, well I'll just write low, cyclic AMP. And since you have low or no cyclic AMP around, well that cyclic AMP isn't going to be able to bind to the catabolite activator protein. And so the catabolite activator protein isn... | Lac operon.mp3 |
I know I'm using a lot of words multiple times. And so it's not going to bond to the activator site, or to the cap site. And so you're going to have less transcription. Less transcription. Transcription. Which once again makes sense. You've got glucose and lactose around. | Lac operon.mp3 |
Less transcription. Transcription. Which once again makes sense. You've got glucose and lactose around. The cell would prefer to use glucose. Simpler sugar. Why waste resources? | Lac operon.mp3 |
You've got glucose and lactose around. The cell would prefer to use glucose. Simpler sugar. Why waste resources? You have plenty of energy around. Just go straight to the glucose. But if you don't have glucose around, well then use more resources so that you can digest the lactose. | Lac operon.mp3 |
And we could leave it at that. We could all go home because we're done. But that's not going to make much of a video. What we really want to ask ourselves is, what is that? What is evolution? And how does it result in biodiversity? I like to think of the study of evolution as following two fairly simple pathways. | Biodiversity and natural selection (2).mp3 |
What we really want to ask ourselves is, what is that? What is evolution? And how does it result in biodiversity? I like to think of the study of evolution as following two fairly simple pathways. These paths are pattern and process. Both of these are not only fascinating areas of study, but are crucial in expanding ou... | Biodiversity and natural selection (2).mp3 |
I like to think of the study of evolution as following two fairly simple pathways. These paths are pattern and process. Both of these are not only fascinating areas of study, but are crucial in expanding our knowledge of how life originated and how it continues to evolve. The pattern pathway studies the shape of evolut... | Biodiversity and natural selection (2).mp3 |
The pattern pathway studies the shape of evolution itself by looking at relationships, relationships among organisms over time. And to do that, you need to create a diagram or structure that links these organisms in time, showing a branching sequence of relationships, much like a family tree or genealogy. These evoluti... | Biodiversity and natural selection (2).mp3 |
Organisms depicted by genealogical trees really are a subject all on their own called phylogenetic systematics. But let's set that aside for a moment. The process path is maybe a slightly better way to start. We want to talk about the mechanisms of evolution, how it actually happens. These are the drivers of the divers... | Biodiversity and natural selection (2).mp3 |
We want to talk about the mechanisms of evolution, how it actually happens. These are the drivers of the diversity along the multitude of lineages that spring out, branching and branching up the tree, up the limbs of the tree of life. Darwin and even some of his predecessors understood this. They could see that things ... | Biodiversity and natural selection (2).mp3 |
They could see that things could change, that the pattern of life, this tree, existed, that evolution happened, and that the relationships among organisms could be traced by looking at features of those organisms and how they changed depending on where they were in the tree. They could see, for example, that the wings ... | Biodiversity and natural selection (2).mp3 |
But at the same time, you could have change among the branches within those lineages. You could get a change in the front leg to a wing or to a grasping arm. General patterns were evident in everything. But at the time, there wasn't a good understanding of the mechanisms, the processes that could explain how these obvi... | Biodiversity and natural selection (2).mp3 |
But at the time, there wasn't a good understanding of the mechanisms, the processes that could explain how these obviously changing, yet related forms could come about. Darwin and his contemporaries read a lot of stuff about variation, which was visible all around them. It could all be seen. They realized that not all ... | Biodiversity and natural selection (2).mp3 |
They realized that not all the individuals in a species or even in a population were exact duplicates of each other. This was a surprise to some people, but the evidence was everywhere, even in things as simple as the speed of racehorses. If you didn't have variation in how fast horses could run, the races would be pre... | Biodiversity and natural selection (2).mp3 |
Races actually demonstrate how horses were chosen for variations in speed. Humans bred fast horses with each other to get even faster horses. And these horses were selected for being the fastest. And that's the key word, selection. Darwin thought, hey, what if nature worked that way? What if nature selected organisms s... | Biodiversity and natural selection (2).mp3 |
And that's the key word, selection. Darwin thought, hey, what if nature worked that way? What if nature selected organisms somehow? He noticed that the form and the physiology and the behavior of plants and animals varied within natural populations just as much as they did in domesticated populations of things like hor... | Biodiversity and natural selection (2).mp3 |
He noticed that the form and the physiology and the behavior of plants and animals varied within natural populations just as much as they did in domesticated populations of things like horses. Darwin realized that what we're really talking about here are the beginnings of the understanding of the evolutionary mechanism... | Biodiversity and natural selection (2).mp3 |
Better, that is, at gathering food, staying away from predators, turning sunlight into usable energy, resisting wind, having good root systems. In other words, fitting the circumstances of the environment and surviving. What Darwin was really saying is that fitness of an individual meant being better able to produce of... | Biodiversity and natural selection (2).mp3 |
This has been referred to as survival of the fittest. Actually, I prefer the phrase survival of the fitter because fittest implies that there's an endpoint, that there's a goal, but there isn't. It's all relative because there are so many compromises and trade-offs in being well suited to a place as complex as the natu... | Biodiversity and natural selection (2).mp3 |
This process of the environment selecting variants that are better suited to that environment, no matter how complex, is called natural selection. And those traits that make the selected variants better able to survive and reproduce and pass on those traits to future generations are known as adaptations. For example, a... | Biodiversity and natural selection (2).mp3 |
This in turn not only increases their individual chances for survival, but it also makes available more energy to the taller redwoods to produce more seeds that carry this tallness trait into future generations. So you get natural selection for a tallness trait and an adaptation to an environment that can present chang... | Biodiversity and natural selection (2).mp3 |
We have to consider, for example, that taller trees might have more trouble getting moisture from the roots all the way up to the tips of those highest branches, or that they could be more exposed to storms that could knock them down, or maybe there's some other physiological cause that we might not even have thought o... | Biodiversity and natural selection (2).mp3 |
Life is never simple. To me, all these aspects come together to represent the great beauties of life, this constant interplay of processes that results in the complexity of biodiversity, what Darwin called grandeur in this view of life. The flip side of this selection coin is that individuals in a population can also b... | Biodiversity and natural selection (2).mp3 |
You might have noticed by now that there's an important element to this story of variation, selection, and adaptation that's missing here. Darwin noticed it too, he was a very smart guy and he fully recognized that there had to be some way by which organisms could pass on those selected traits, those adaptations to the... | Biodiversity and natural selection (2).mp3 |
There had to be a way that the offspring of individuals that had been selected for could inherit the traits of their successful parents and ancestors. In Darwin's day, there wasn't a good understanding of a mechanism for that. It was only much later that scientists discovered how information is stored in genetic materi... | Biodiversity and natural selection (2).mp3 |
Today, our detailed understanding of evolutionary processes is built on the discoveries of both Darwin and geneticists. Stepping back now to put it all together, we can see that for all this to work, several different things have to be going on. You have to have variation in nature among the members of a population. Yo... | Biodiversity and natural selection (2).mp3 |
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 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 all the m... | Natural Selection and the Owl Butterfly.mp3 |
And then if you came a little bit later and you saw 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 the point I was making there is that, look, that wasn't engineered or an explicit move on the part of the moths or the D... | Natural Selection and the Owl Butterfly.mp3 |
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 I have a couple of pictures of what's commonly called the owl butterfly. And what'... | Natural Selection and the Owl Butterfly.mp3 |
So for example, here I have a couple of pictures of 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 that its wing looks like half of an owl's eye. I mean, I can almost draw a beak here and draw another wing there, and you can im... | Natural Selection and the Owl Butterfly.mp3 |
And here, too, I can imagine a beak here, and you would think an owl in there, too. And so the question is, how does something this good show up randomly? I mean, you could imagine, OK, little spots or black and white or gray, but how does something that looks so much like an eye generate randomly? Now, the answer is, ... | Natural Selection and the Owl Butterfly.mp3 |
Now, the answer is, well, there's a couple of answers. One is, why does this eye exist, or this eye-like pattern, or this owl-like eyes pattern? And there, the jury's still out on that. I read a little bit about it on Wikipedia, and these are all of these images I got from Wikipedia. And Wikipedia, they said, look, the... | Natural Selection and the Owl Butterfly.mp3 |
I read a little bit about it on Wikipedia, and these are all of these images I got from Wikipedia. And Wikipedia, they said, look, there's two competing theories here. One theory is that this, 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 k... | Natural Selection and the Owl Butterfly.mp3 |
That this is, you know, when some predator is about to chase 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 butterfly's body, which doesn't look that substantive, they go for the big black thing. They say, oh, that looks like it's protein-... | Natural Selection and the Owl Butterfly.mp3 |
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 animal itself, the actual butterfly, would survive, and maybe it can repair its wings. I don't know the actual biology of the owl butterfly. That's one theory, and ... | Natural Selection and the Owl Butterfly.mp3 |
You'd want it back here instead of right here, because there's still a chance if something chomps at this little black spot that it'll still get the abdomen of the butterfly. Now, 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 o... | Natural Selection and the Owl Butterfly.mp3 |
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 are likely to eat this dude. So maybe if, and it does turn out in my reading, that they are lizards that like to eat these type ... | Natural Selection and the Owl Butterfly.mp3 |
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