Natural Selection and Evolution: Videos & Practice Problems

Natural selection is a process where the environment selects organisms with advantageous traits, enhancing their fitness, defined as the ability to survive and reproduce. Adaptation results from this selection, leading to evolutionary changes in a population's DNA over generations. For example, in a population of crickets, brown individuals may survive better against predation than green ones, illustrating how natural selection drives evolution and biodiversity. Understanding these concepts is crucial for grasping the mechanisms behind life's diversity on Earth.

Adaptation Improves Fitness

In this video, we're going to begin our lesson on natural selection and evolution. But before we define natural selection and evolution, it's first helpful to define adaptation and fitness and how the adaptation of an organism to its environment helps to improve that organism's fitness in that environment. Now, you may have already noticed that living organisms throughout our world are very well suited to the environments that you can find them in, and this is due to adaptation. And so adaptation can be defined as the process that enables organisms to improve survival and reproduction in their environments. And so this leads us to the term fitness.

Now, the term fitness is used by scientists and biologists in a very different way than the term is used in our everyday language. And so, the term fitness, in this case, does not refer to how long you can run on a treadmill, how big your biceps are, or if you have a six-pack or not. Instead, fitness, in this case, refers to an organism's ability to survive and reproduce. And so, really, adaptation is the process that enables an organism to improve its fitness or ability to survive and reproduce in its environment.

And so, if we take a look at our image down below, what you'll notice is we have a variety of different types of organisms that are very well adapted to their environment and have very high fitness in their environments. And so, for example, penguins are very well adapted to cold snowy environments and so are polar bears. However, camels are very well adapted and have high fitness in hot and dry climates. Now here, this looks like a leaf. However, what you'll notice is that this is actually an insect that has adapted to its environment, and so if we zoom in here, you'll be able to see this insect a little better. Now, snakes are also very well adapted to their environments as well, and so adaptation is really just a process that enables organisms to improve their fitness.

And so, this here concludes our brief introduction to adaptation and how it improves fitness, and in our next video, we'll be able to talk more about natural selection and evolution. And so, I'll see you all in that video.

Natural Selection Causes Adaptation

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 1800s. And really the process of natural selection is exactly what it sounds like. It's when the natural environment selects for very specific organisms within a population that are more 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 are more 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 two 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 to 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 going to 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 the population of giraffes and notice that on the far left, we're looking at a time scale that is early early on, some 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, there was genetic diversity within this population of giraffes. And so you can see that we had some short-neck giraffes like this one over here, we had some medium-neck giraffes like this one here, and some long-neck giraffes like this one 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 giraffes here are all eating from this same tree but what you'll notice is the short-neck giraffe can only access the leaves on the tree that are really low. However, the other two giraffes, the medium-neck, and the long-neck giraffe, 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 are 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 are higher up and there's no more food down below. And so ultimately, this giraffe is not going to be able to survive and reproduce as well as these other ones because of the natural environment selecting for these organisms that have a little bit longer necks. And so this short-neck 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 is capable of eating this layer as well and so there's going to be a 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-neck giraffe, although it lasted longer than the shorter-neck giraffe, it ultimately is also sadly going to pass away. And so the only giraffes that are left are the ones that were capable of reaching the top of the tree, where there was plenty of food. And notice 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 and reproduce as well as the longer-necked giraffes which had more 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 necks. And that's why, today when you go to the zoo, giraffes have such long necks because of this process of natural selection. And so this here really concludes our introduction to natural selection and how this causes adaptation. Again, because this giraffe 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.

Which of the following is true of natural selection?

• A. It requires genetic variation.
• B. It requires selective pressure from the environment.
• C. It involves differential reproductive success.
• D. a, b, & c

Answer: (D)

Evolution can Occur Via Natural Selection

So now that we've introduced adaptation, fitness, and natural selection in our previous lesson videos, in this video, we're going to briefly discuss evolution and how one of the ways that evolution can occur is via natural selection. And so many people have a preconceived idea of what evolution is through watching sci-fi TV shows and things like that. But really, scientists define evolution in a very specific way. And so, evolution is referring to changes in the DNA of a population over multiple generations which really means over long periods of time. And so, really evolution is just the change in the DNA of a population over long periods of time. Now, evolution can occur in a wide variety of many different ways. But what you guys should know for this video is that one of the ways that evolution can occur is via natural selection. Now, evolution, again the change in the DNA of a population over long periods of time, has affected and shaped all life on earth and therefore it's actually responsible for life's tremendous diversity.

And so if we take a look at our image down below, which you'll notice is we're showing you an example of evolution by natural selection. And this image is going to be very similar in many ways to the image that we showed with the giraffes for natural selection in our previous lesson videos. And so what you'll notice in this image is that we have in this box over here we have these birds and then we have these crickets down below. And what you'll notice is that these birds are hungry and they are eating the crickets for food. And what you'll also notice is that when we take a closer look at these crickets, most of the crickets are green in color. However, there are some crickets that are a brownish color. And so we should note here that mostly, there are green crickets in the population on the left-hand side.

Now what you'll notice is that the background that these crickets are on is tannish brownish colored background. And so the tannish brownish colored crickets tend to blend into their background much better. And the greenish crickets are much more exposed, and there's a lot more contrast with the background and so the birds are able to visualize and eat the green crickets much easier. And so generations later with this selective pressure of the birds eating the crickets, the birds will continuously eat the green crickets more than the brown ones simply because the green crickets can be visualized better. And so the brown crickets are going to have improved fitness, improved ability to survive and reproduce. And so, notice that the population is beginning to change and there are more brown crickets than there are green crickets, again generations later. And if this selective pressure continues, then even more generations later, the entire population of crickets can become brown and all of the green crickets may go extinct. And so, here what we can say is that there are mostly brown crickets in the population.

And so this is an example of evolution because the population has changed its DNA from the DNA that codes for green crickets mostly to the DNA that codes for brown crickets mostly. And this is an example of natural selection by evolution. And so this concludes our brief discussion on evolution and how it can occur via natural selection, and we'll be able to get some practice applying this as we move forward. So I'll see you all in our next video.

Evolution through natural selection will occur most rapidly for populations of plants that:

• A. Are already well adapted to the environment.
• B. Reproduce sexually and live in an unstable environment.
• C. Live in an unchanging environment.
• D. Are in the same genus.

Answer: (B)

Charles Darwin's theory of evolution by natural selection explains all of the following EXCEPT:

• A. How an ecosystem decays over time.
• B. How inherited traits are passed from parent to offspring.
• C. How the DNA of a population can change over time.
• D. How evolution takes place in the natural world.

Answer: (A)

Here’s what students ask on this topic:

What is natural selection and how does it work?

Natural selection is a process first described by Charles Darwin, where the natural environment selects organisms with advantageous traits, enhancing their fitness, which is defined as the ability to survive and reproduce. This process requires genetic diversity within a population and selective pressure for heritable traits that affect fitness. For example, in a population of giraffes, those with longer necks can access more food and are more likely to survive and reproduce. Over time, these advantageous traits become more common in the population, leading to adaptation and evolutionary changes.

How does adaptation improve an organism's fitness?

Adaptation is the process that enables organisms to improve their survival and reproduction in their environments, thereby enhancing their fitness. Fitness, in this context, refers to an organism's ability to survive and reproduce. For instance, penguins are adapted to cold, snowy environments, which improves their fitness in such climates. Similarly, camels are adapted to hot, dry climates, enhancing their fitness in those conditions. Adaptations can be structural, behavioral, or physiological, and they help organisms better exploit their environments, leading to higher survival and reproductive success.

What are the requirements for natural selection to occur?

Natural selection requires two main conditions: genetic diversity within a population and selective pressure for heritable traits that affect fitness. Genetic diversity means that individuals within a population have different features or traits. Selective pressure refers to environmental factors that favor certain traits over others. These traits must be heritable, meaning they can be passed on to the next generation. For example, in a population of crickets, brown crickets may survive better against predation than green ones, leading to a higher frequency of brown crickets over generations.

How does natural selection lead to evolution?

Natural selection leads to evolution by causing changes in the DNA of a population over multiple generations. As the environment selects for organisms with advantageous traits, these traits become more common in the population. Over long periods, this process results in significant changes in the population's genetic makeup. For example, if brown crickets survive better than green crickets due to predation, the population will gradually shift to having more brown crickets. This change in the population's DNA over time is evolution, driven by natural selection.

What is the difference between adaptation and evolution?

Adaptation and evolution are related but distinct concepts. Adaptation refers to the process by which organisms become better suited to their environment, improving their fitness. It involves changes in traits that enhance survival and reproduction. Evolution, on the other hand, is the change in the DNA of a population over multiple generations, leading to the development of new species and biodiversity. While adaptation is a result of natural selection acting on individual traits, evolution encompasses the broader genetic changes in a population over time.