Natural Selection and Evolution

in this video, we're going to begin our lesson on natural selection and evolution. But before we can actually define natural selection and evolution, we first need to introduce adaptation of living organisms and how adaptation leads to improved fitness of the organisms. And so, as you guys have probably already realized, living organisms are really well suited to their environments, and this is due to adaptation. And so adaptation is really defined as the process that enables living organisms to improve their survival and reproduction in their environments. And so this penguin that we're showing you down here is really, really well suited to it's extremely cold environment. And so although the environment that the penguin lives in is extremely cold, the penguin is still able to remain warm in these cold environments. And so the penguin is really well adapted or really well suited to its environment, and it's capable of surviving and reproducing in its environment. Whereas the camel over here is really, really well suited to its environment, which is going to be a hot and dry desert, and the camels have adapted in such a way where their humps contain water that allow them to sustain and survive and reproduce, and they're extremely hot and dry climates. And although this here might look like a leaf, it's actually an insect that has adapted to its leafy environment in a forest on this allows it to survive and reproduce and its environment. And, of course, polar bears and snakes and all living organisms are really well suited and adapted to their environment so that they can improve their survival and reproduction. Now the term fitness, when used by biologists, is very different than the way that you and I might use the term fitness in our everyday life. And so fitness is not referring to an animal's six pack or anything like that. Instead, fitness, when used by biologists, is referring to an organism's ability to both survive and reproduce. And so when we say that adaptation is the process that enables and organisms to improve survival and reproduction, we could also say that it's the process that enables organisms to improve fitness, and that's exactly what we're seeing up above here. That adaptation improves the fitness, and so this here concludes our introduction to adaptation and how it improves fitness, and in our next lesson, video will be able to introduce natural selection. So I'll see you guys in that video

So in our last lesson video, we talked about how organisms are really well adapted to their environments because of adaptation and how adaptation improves the fitness of organisms. And so in this video, we're going to talk about how natural selection actually causes adaptation or, in other words, how adaptation is really just the result of the process of natural selection. Now, natural selection once again is a process that was first described by the scientist Charles Darwin, way back in the 18 hundreds. And really, the process of natural selection is exactly what it sounds like. It's when the natural environment select for very specific organisms within a population that are mawr fit to their environment. And once again, this word fit here is different than the way that we would use fit in our everyday language. Fit does not mean you have a big bicep. Instead, Fit is referring to the survival and reproduction of an organism, and so if organisms arm or fit, they are more capable of surviving and reproducing. And so, in other words, we can say that natural selection is pretty much survival of the fittest, So the organisms that are most fit to their environment are the ones that will survive and be able to pass on their genes to the next generation. Now natural selection has to requirements that we are going to talk about down below right here Now. The first requirement of natural selection is that there must be genetic diversity within a population and by genetic diversity. All this means is that within a population there has to be organisms that have different features. And so you can think that there's going toe always be genetic diversity within a population. I mean, think about your own family. For instance. Are you exactly the same as your parents, or do you look a little bit different? Of course, you're going to look a little bit different because you are genetically different. There's genetic diversity within between you and your parents. And so even within a population, for instance, of giraffes, there's always gonna be a little bit of genetic diversity. So this is something that's always going to be the case now. The second requirement for natural selection is that there must be some kind of selective pressure for heritable traits that affect fitness, and so by heritable, what it means is that these traits can be passed on to the next generation. And again, fitness is referring to the survival and reproduction of organisms and so down below. What we have is a classic example of natural selection. And so we're taking a look here at a population of giraffes and noticed that on the far left we're looking at a time scale that is early, early on some thousands and thousands of years ago. And over here, what we have is the present. And so this represents our time scale. And so notice that early on, thousands of years ago, uh, there was genetic diversity within this population of drafts. And so you can see that we had some short neck drafts like this one over here. We had some medium neck draft like this one here and some longneck draft like this one over here. Now again, in the process of natural selection, the natural environment is going to select for very specific organisms that have traits that allow them to survive better. And so what you'll realize is that these drafts here are all eating from this same tree. But which will notice is the short neck draft can Onley access the leaves on the tree. That air really, really low, However, the other two giraffes the medium neck and long neck draft they can eat from the lower portions and from higher portions as well. And so what this means is that very quickly the leaves on the bottom are going to disappear a lot faster than the leaves that air higher up. And so pretty quickly here, this short necked giraffe is going to run out of food on the bottom. And so notice he's realizing. He's like, Wait, guys, I can't reach these leaves that air higher up and there's no more food down below. And so, ultimately, this draft is not going to be able to survive and reproduce as well as these other ones because of the natural environment is selecting for thes organisms that have a little bit longer next? And so this short necked giraffe, unfortunately, has to pass away, and then this other medium neck giraffe starts to realize what's happening, and he's like, Oh, shoot! And he's realizing that this layer of leaves here is also going to run out of food because this giraffe eyes capable of eating this layer as well. And so there's going to be, ah, lot more food at the top, and this layer of leaves is going to go away pretty quickly and so very similarly to the previous situation. This medium necked giraffe. Although it lasted longer than the shorter necked giraffe, it ultimately is also, sadly, going to pass away. And so the Onley giraffes that are left are the ones that were capable of reaching the top of the tree, where there was plenty of food and noticed that the leaves and all the other areas are all gone. And that is why these shorter neck giraffes passed away because they couldn't survive, uh, and reproduce as well as the longer next draft, which had Mawr access to more food. And so he's wondering, Where did everybody go? And so this is the process of natural selection again, how the natural environment, like, for instance, just the height of the leaves on this tree, is naturally selecting for organisms for giraffes that have longer next. And that's why today, when you go to the zoo, giraffes have such long next because of this process of natural selection, And so this year really concludes our, uh, introduction to natural selection and how this causes adaptation again because this draft is very well adapted to its environment, being able to access food at higher levels. And in our next video, we're going to talk about how natural selection ties into evolution, So I'll see you guys there.

So now that we've discussed adaptation, fitness and natural selection in this video, we're going to define evolution and talk about how one of the ways that evolution can occur is via natural selection. And so most people have some preconceived idea of what evolution is through watching fictional sci fi TV shows and cartoons and things like that. And so maybe you guys think an example of evolution would be a pair of wings popping out of my back and me floating away like a little butterfly. However, that is not what evolution is about at all. Evolution does not have anything to do with physical changes. Instead, scientists define evolution in a very specific way, and so evolution is defined by scientists as changes in the D N A. Of a population over multiple generations or over long periods of time. And so really, evolution just means changes in the DNA of a population. And so again, changes in the DNA of a population may or may not result in physical changes. And so this is how you should know evolution is defined now. Evolution can occur in a wide variety of different ways. But what you guys should know is that one of the ways that evolution can occur is via natural selection, which we already discussed in our last lesson. Video now evolution. The changes in DNA of a population over long periods of time has shaped all life on Earth. And really, evolution is what is responsible for life's incredible diversity and so down below. In our example right here, we're going to look at an example of evolution by natural selection. And really, this image that we see right here is an example of natural selection. And it's very similar in many ways to the natural selection image that we showed with giraffes in our previous lesson video. And so they're both showing classic examples of natural selection. But here we're specifically showing natural selection in the context of evolution. And so what I want you guys to notice is down below. In our image, we have this population here of beetles and notice that within this population of beetles, we have some genetic diversity. We have these green or dark beetles, and then we also have these orangish light colored beetles. And another thing for you to notice is that the background or The natural environment that these beetles are in is pretty light colored. It's a tan color. And so, uh, one thing toe. Also note is that most of the Beatles in this population are dark Beatles, their dark greenish beetles that you see here. And so that's something important to note here. Now. Notice also that we have these birds here, and the birds are feeding on these on this population of beetles. However, because the natural background the natural environment is light colored, these birds can see the dark beetles so much easier than they can see the light colored orangish beetles. And so because they can see the dark colored beetles a lot easier, these birds are just going thio eat the dark colored Beatles mawr often than they eat the light colored beetles. And so generations later, if this selective pressure of the birds eating the dark Beatles continues toe happen over long periods of time. Ultimately, what we'll have is an evolving population of beetles. Notice that their arm or orange Beatles showing up over time because these orange beetles have a lot, uh, a higher likelihood of surviving and reproducing since they blend into their natural background. Ah, lot better than the dark beetles do. And so the reason that this is an evolving population of beetles is because noticed that the DNA of the population is starting to change over long periods of time. Generations later here we have mostly dark beetles, and over here this population is starting to evolve because the DNA in the population is starting to change to these orange colored, uh, beetles, the DNA in the orange colored beetles. And so if these birds continue Thio, eat all of these dark Beatles, uh, generations later, over long, long, long periods of time, Eventually all of the dark beetles will be gone. And on Lee, the orange beetles will remain. And again, the orange Beatles air here because they blend in to their environment better and they're therefore able to survive and reproduce better. And so what we have now over here on this side is mostly the light or the orange colored beetles. And so what we can see is that we've gone from mostly dark Beatles, uh, in the population of beetles to mostly light Beatles over here over time. And so this here because we have a change in the DNA of the population over multiple generations. DNA that allows for dark beetles mostly, uh, changing thio DNA for light Beatles within the population. This is a classic example of evolution, but by natural selection. And so this year concludes our lesson on evolution and how it can occur via natural selection, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you guys in our next video.