Lesson video

Hi, I'm Mr. Buckingham and I'm so glad you've decided to join me for today's lesson.

Now, today's a big one because you're gonna be learning about one of the most important scientific theories in history, Charles Darwin's Theory of Evolution by Natural Selection.

I think you're going to find it fascinating.

So let's get going.

Today's lesson is called Researching Darwin's Theory of Evolution from our unit called Charles Darwin, Biographical Writing.

By the end of today's lesson, we'll be able to explain the theory of evolution by natural selection, giving examples of how it has led to animals having certain characteristics.

Now you may already know lots of information about Charles Darwin's life.

Today we're going to be learning about his contributions to science, the things he discovered that have changed our understanding of the world, and all of that knowledge is going to feed into our writing of a biography about him.

Let's get to work.

Here are our keywords for today's lesson.

My turn, your turn.

Variations, natural selection, offspring, and evolution.

Well done.

So variations are differences between individuals in a particular species and natural selection is the theory that living things with characteristics that help them survive in a particular environment will pass these characteristics on to their offspring.

And offspring is a living things young.

Evolution is the way living things change and develop over millions of years.

So here's our lesson outline for today.

We're going to start off by trying to understand Darwin's theory of the evolution by actual selection, and then we'll apply it to Darwin's finches, which were birds that he discovered in the Galapagos Islands.

So we are going to be writing, as you know, a biography of Charles Darwin.

We see a picture of him in his later life here.

Now a biography usually refers to a person's major achievements or their contributions to the world.

It doesn't necessarily worry about little facts about things they might have done later on in life.

It focuses in on their big contributions.

And for Darwin, that's the theory of evolution by natural selection, which was a world-changing discovery.

It was world-changing at the time and it still changes our understanding of the world today, and still has a big impact on how we think about the world.

Now we know that Darwin went to the Galapagos Island on HMS Beagle on its way back to England, and after he returned from the Galapagos to England in 1836, he spent many years thinking about what he'd seen.

And at that time, it's important to note that most people in the UK at least believed that a God had created living things long ago and that they had stayed the same ever since.

And that's a really important point.

So for instance, God had created giraffes to look exactly as they do now, and they had stayed the same since that period of time.

So Darwin thought about the finches that he'd seen in the Galapagos Islands and you can see an example of one of these finches here.

Now remember, the different species of finch on each island looked very similar.

So they must have been related to each other in some way.

But on each island, the finches had different shaped beaks, and those beaks were perfectly adapted for the food found there.

So if the main food on one island was large nuts, then the birds on that island might have had large beaks.

If the food on the other island were small seeds, then the finches on the island might have had much smaller beaks, which are better-adapted for those small seeds.

So Darwin had a question to answer.

How had the finches ended up being so well-adapted to their particular island and to its food sources, even though they seemed to be related to each other because they looked so similar.

So what did Darwin notice about the Galapagos finches? Pause the video and see if you can find all the correct answers.

Well done.

Good job.

So yes, they looked very similar in most ways.

No, they didn't look completely different.

Yes, the finches on different islands had differently shaped beaks.

And yes, you're right, the beaks were well-adapted for the food on each island.

Really good job.

So can you think now of any animals that are well-adapted to their environment or their lifestyle and how are they well-adapted to them? Pause the video and have a think of some examples.

Well done.

Good job.

So here are some examples of advantageous adaptations, beneficial adaptations that animals have for their environment.

For instance, fish can breathe underwater through gills.

Many whales can filter water to remove food from it, like krill.

And camels can go over six months without drinking, which is really helpful if you live in the desert.

Sharks can smell blood from several miles away.

That's a scary one.

And elephants, huge ears help 'em to cool down by flapping them, they can cool down and they live in very hot environments, so that is beneficial or advantageous.

So we can see lots of animals seem to have adaptations which are helpful to them.

How has this ended up being the case? That's what Darwin is trying to work out.

So after many years, Darwin came up with the theory of evolution by natural selection to explain what he had seen, to explain how animals appeared to have been adapted to the environments and the lifestyles that they had.

So the theory starts with two really important ideas and the first one is variation.

So individuals in a species are not identical.

There's variation between them in things like colour, size, the shape of different body parts, and so on.

Many, many features of a person or an animal's body or a plant's form can have variation between individuals in a species.

And there's competition between these individuals in the natural world, there might be competition for food, there might be competition for space, there might be competition for mates.

So individuals have variations between them and they're competing with each other for food, for space, for mates.

So what variations do we see in the population of humans? Pause the video and have a chat to the person next to you.

Or have a think on your own.

Well done.

There's loads aren't there? I bet if you looked around your classroom, you would see the huge variation there is between individuals within our species of humans.

And it's the same with animals and with plants, there is variation between the individuals in a species.

So what variations might we see in a population of lions? Here's an example.

We might see variation in the thickness of their fur.

Some will have slightly thicker fur and some might have slightly thinner fur.

Can you think of any other variations there might be in a lion population? Pause the video and have a think.

Well done.

Good job.

So here are some examples of the variations we might see.

You might see variations in the size of their teeth.

Some might have slightly bigger and some slightly smaller teeth, maybe in the size of their claws, the size of their mane, the colour of their fur, the size of different muscles, and the strength of those different muscles.

And even in the strength of their jaws maybe.

So you can see that there might be lots and lots of variations between different individuals inside the species of lion.

And remember, those individuals are competing against each other for food, for space, and for mates.

So the theory of evolution by natural selection continues like this.

So when those individuals with variations are competing in the wild, those whose variations make them better-adapted will win.

So the ones whose variations are better-adapted to their environment and their lifestyle will win.

That means they will do better.

So that means they're going to get more resources, more food, more mates, more space, and they're going to survive longer.

So we can sum it up by saying they are more successful.

So if your variations make you better-adapted to your environment and your lifestyle, you are more successful.

You might live longer, you might have more mates, you might have more food.

So sometimes we call this idea survival of the fittest.

Why might this be? Pause the video and have a chat to the person next to you.

Well done.

Good ideas.

So what it actually means is that the individuals that have the best fit with their environment are the most likely to survive for longer.

So it might be to do with being fit in the way we think of being fit, like exercising, but really we're talking about how well they fit in to their environment.

So if you have a really good fit with your environment, then you're likely to survive longer and be more successful in the ways we've talked about.

So how might each of these variations between lions affect how well they can compete with each other in the wild? So how might a variation in running speed affect how they compete? How could a variation in jaw strength affect how they compete? And what about the colour of their fur? How could each of these variations have an impact on which lions are most successful and why? Pause the video and have a think.

Well done, good thinking.

So for running speed, we could say, well, the lions which are fast at running are likely to be able to catch prey more easily so they'll be more successful.

For jaw strength, we could say lions with stronger jaws might be more effective at killing their prey.

So again, they're more successful.

And for the colour of their fur, maybe lions which are better camouflaged with the habitat might be better at hunting and therefore they're going to be more successful at hunting as well.

Really well done if you've managed to think of some similar ideas.

So here are the final steps in Darwin's theory because those individuals with better adaptive variations are being more successful, and they're living longer, and they're better nourished, they've got more food, they're more likely to reproduce, have offspring, so that offspring will inherit the variations that made them better-adapted.

Now we now know that this is to do with what we call genetics, which you might have heard of.

Now they didn't know that at the time Darwin was making this theory, so we're going to put that to one side.

But they did realise that some traits could be inherited from parent to child, from parent to offspring.

So these better-adapted traits are passed on from parents to offspring.

And over many generations, those better-adapted variations will become normal in the population.

So the species has changed because those better-adapted variations have become the normal thing to be in that species.

Now, this is a gradual change.

It can take thousands or even millions of years for this to happen.

And this is what we call evolution, where a species gradually changes over very long period of time for those better-adapted variations to become normal in the population.

So let's summarise the process of evolution by natural selection.

And bear in mind this is a summary.

If we were doing science, we'll go into a bit more detail.

So we are summarising here with the main points.

So first of all, we know there are variations between animals in a species in a particular habitat, and these animals are competing against each other for resources.

And animals whose variations make them better-adapted for their environment are more likely to be successful in getting those resources.

And that means they're more likely to survive.

And that means they have more opportunities to reproduce.

And when they reproduce, they're passing on those useful variations, those beneficial variations to their offspring, to their children.

And then over many generations, perhaps hundreds or thousands of generations, these useful variations become normal in the species or they can lead to the creation of new species altogether.

Because what happens is over these many generations, the change, the variation can become slightly more and more and more pronounced.

It can become more significant.

So over time, the change in the animal can be so significant that we can consider it a new species, but that would take an enormous, enormous amount of time.

So do bear in mind, these changes are happening over enormous periods of time.

So can you put the steps of evolution by natural selection in order, pause the video and have a go? Well done.

So again, to start with this one, we've got some animals in a species have a helpful variation and then this variation makes those animals more successful.

Then, these successful animals pass on their variation to more offspring.

And finally, over many generations the variation becomes normal for the species.

Really well done if you got this right.

Okay, now let's imagine a lion.

And this lion has been born with no claws as a random variation.

Can you explain why it'd be unlikely to pass on this variation to offspring? Pause the video and have a think Well done, good thinking.

So first of all, remember that lion is competing for food with other lions that do have claws.

So the lion with claws is going to be much better-adapted for its environment and they can hunt much more successfully than our poor lion who has no claws.

So the clawless lion is going to struggle to get food and then, as a result, gonna struggle to get mates and it might struggle to survive at all.

And this means it's less likely to find mates and to reproduce.

And that means it's unlikely to pass on the variation of having no claws to any offspring.

So it's not likely to become a common variation in the lion population overall.

So we can see that this is how an unuseful and unhelpful variation might not be passed on to offspring and might not become common in the population.

Really well done if you worked that out.

So now let's consider the example of a gerbil.

A gerbil evolving its appearance to be better-adapted to its environment.

And remember, this process is over a huge period of time.

So let's imagine we've got a group of dark brown gerbils whose habitat has changed to become a desert.

Now in the desert sands, being dark brown is not gonna be helpful, is it? Because you're gonna stand out really clearly and that means snakes can catch them easily because they're not camouflaged well.

And because of natural variation, we are not gonna have all gerbils the exact same colour.

There are gonna be some gerbils which are more light-colored.

Now these gerbils in the desert sands are going to be harder for snakes to see.

So they're going to survive longer.

And that means they can reproduce more and their offspring are going to inherit the variation of being light-colored.

So over many generations, we're going to see that being light-colored becomes normal for the gerbil species.

So we've seen how a variation can become normal over a long period of time.

So let's see if you can retell that explanation really clearly.

Can you explain how the gerbil species may have evolved to have more light-colored fur over a very long period of time? Pause the video and have a try.

Well done.

Good effort.

So maybe you start off by saying, well, having dark fur was not a good variation in the desert.

And gerbils with dark fur are going to be caught more easily by predators like the snakes.

That meant that gerbils with the variation of light-fur were better-adapted to their environment because they were not so easily caught.

Then these light-fur gerbils were more likely to survive and pass on their light-fur variation to their offspring.

And finally, over time, having light-fur would become normal for gerbils.

Really well done if you managed to retell those series of events.

So let's do our first task for the session.

And here we're just going to be talking and explaining.

So we're not going to write anything.

Let's consider the giraffe.

Can you use Darwin's theory of evolution by natural selection to explain how the giraffe might have evolved such a long neck? I want you to begin by imagining an ancient ancestor of the giraffe that had a normal-length neck, a bit like a horse.

And this giraffe moved to an area where the trees are tall with few low-growing leaves.

And I want you to explain how over a long time this might have led the giraffe species to evolve to have a long neck.

And you might want to use words like these.

We've got variation, competition, and offspring.

So pause the video and see if you can apply your knowledge of Darwin's theory of evolution by natural selection to explain how a giraffe might have evolved such a long neck.

Have a go.

Well done, fantastic effort.

So here's a suggestion for how this may have happened.

Maybe there was variation between giraffes, some would have longer necks and some would have shorter neck.

And then in the new habitat where they've moved to, having the variation of being longer necked is going to be helpful because these giraffes can reach the higher leaves and they can eat more.

And then the giraffes with a long neck variation are going to be more successful.

They'll survive longer and they will reproduce more and they're going to pass on the variation to their offspring.

And over a long time, a huge period of time, remember, having a long neck is going to become normal for giraffes.

Now you can see going from a horse-length neck to a giraffe-length neck is a huge change.

And that would mean a change in the species itself.

It would become a new species.

So that is going to take an enormous amount of time.

And you can see there that the variation has been strengthened over time.

It's become more and more pronounced over this vast period of time as the species have evolved.

Really well done if you've managed to explain that clearly.

So we've talked about Darwin's theory of evolution by natural selection.

Now let's go back to those finches that he found on the Galapagos Islands.

So we can see that we've got our Galapagos Finch here that Darwin observed and collected, in fact, when he visited the Galapagos Islands.

And remember, these birds were very similar, but on each different island the finches had different shaped beaks.

And the finches beaks were well-adapted to eat the food that was common on the island where they lived.

For example, if large seeds were common on one island, then the finches there would have large, strong beaks that could break them open.

So now that you've got some new knowledge, how might this have happened? Pause the video and have a chat with the person next to you.

Well done.

Good effort.

So I bet some of you have already thought this through in great detail.

Well done.

So let's imagine that a group of finches with generally small beaks migrates or travels to an island in the Galapagos and the island where birds land has very few small seeds.

Actually, most of the seeds there are very large.

So within this group of birds, as I'm sure you've thought already, there is gonna be variation.

Some of their beaks are slightly larger and some are going to be slightly smaller.

So all the birds can just about manage to eat these large seeds.

But it's easier for those with slightly larger beaks.

You can see where this is going.

So the birds with slightly larger beaks are going to be more successful, aren't they? So they're going to reproduce more, passing on their larger beak variation to their offspring.

So over many generations, larger beaks are going to evolve to become normal on that island.

So we've got the finches on this particular island where we've got large seeds will evolve over many, many, many generations to have slightly larger beaks.

So which of the following is the best explanation for how the finches beaks came to be well-adapted to the food available? Pause the video, read the options carefully, and decide which is the best explanation.

Have a go.

Well done.

Good job.

Hopefully, you spotted that it is C.

Over many generations, the birds' beaks evolved because having a particular beak was an advantage on a particular island.

It made those birds more successful because they were more successful they could reproduce more, and because they could reproduce more, more offspring had that variation.

Really well done if you've got that one.

So now can you put these events in order to describe how the birds may have evolved larger beaks over many generations? Pause the video and have a try.

Well done.

Hopefully, you started with this one.

The birds migrate to an island where most of the seeds are larger, then the birds with slightly larger beaks are more successful than those with smaller beaks.

Then the larger-beaked birds live longer and reproduce more, and finally, they offspring inherit the larger beaks and are also more successful.

So over time, the species evolves.

Really well done for getting those.

So we talked about Darwin's theory.

Let's think about how he publicised his ideas, well, you can see a copy here of his most important publication.

This is a book called "On the Origin of Species", which Darwin published in 1859, setting out his ideas about evolution by natural selection.

And it had a huge impact at the time because it challenged many people's ideas about how living things had come to be.

Remember, many people at the time thought that a God had created the living things in the world and they had stayed the same since then.

And Darwin's theories obviously challenged that view and these ideas inside the book also sparked or created a huge amount of scientific investigation.

So many more scientists wanted to explore these ideas as well.

Now, because of this, Darwin is considered to be the father, if you like, of the theory of evolution.

And he and his theory are now known all over the world.

So he had a huge legacy and a huge impact on our understanding of the world as it is.

So now that we know about Daren's theory, let's complete our final task for this lesson, I'd like you to complete the sentences to explain how the finches could have developed larger beaks over time through natural selection.

And you can see all the words you need on the right-hand side.

Pause the video and have a go.

Well done, fantastic effort.

So let's put the words in the correct place in this paragraph, we've said a group of birds migrates to an island where most seeds are large.

There is variation in the size of the bird's beaks.

Some are smaller and some are, well done, larger.

The birds with larger beaks are more, good, successful in the new habitat because it is easier for them to eat the seeds.

As a result, they survive longer and can, well done, reproduce more.

Their offspring inherit their larger beaks.

Over time, having a large beak becomes normal in the population of birds on this island.

So evolution by natural selection has taken place, fantastic effort.

So let's summarise our learning in this lesson.

We learned that Darwin is best known for his theory of evolution by natural selection.

We learned that this theory describes how animal species can change over time to become better-adapted to their environment.

And we learned that Darwin's observations of the finches in the Galapagos Islands helped him to understand how evolution might happen over very long periods of time.

I'm really impressed with the outfit in this lesson.

Fantastic job learning this detailed information about evolution, I'd love to see you again in a future lesson.

Goodbye.