Lesson video

Hello there, and welcome to this lesson from the Oak National Academy.

Today's lesson is taken from the unit Adaptations, competition, natural selection and evolution, and the title of today's lesson is Evolution.

Hi there, I'm Mrs. We, and I'm gonna be your teacher for today's lesson.

Before we get started, I wanted to acknowledge that I know this is a sensitive issue for some people.

There are lots of really strong opinions about how the diversity of life we see around us came into existence.

And what we're talking about today is how scientists explain, how the vast majority of scientists explain evolution, and that's something you'll need to be able to do in your exams. You'll need to be able to explain evolution.

But you might know some people who've got different opinions and different ideas about it, and that's totally fine.

It is really normal for people to disagree about things.

And whilst we can still hold and feel strongly about those disagreements, it's really important that we stay respectful of each other and our different ideas.

Okay, let's get started.

By the end of today's lesson, you'll be able to explain the theory of evolution by natural selection.

Let's have a look at our keywords.

We have three keywords for today's lesson.

We have theory, evolution, and natural selection.

So before I show you those definitions, I just wanna remind you that you don't need to try and rush and memorise these all straight away.

I'll be quiet for five seconds so you can read them through, or if you want a bit longer, you can pause the video, read them through, write them down, whatever suits you, and then click play when you're ready to see the rest of the lesson.

Today's lesson is in three parts.

You might have heard someone say before evolution is just a theory, and that's what we'll be talking about in the first part of today's lesson.

Next we'll talk about a really common example, a really famous example of evolution by natural selection.

And finally, we'll talk about some common misconceptions that people have about evolution.

But before anything else, let's talk about this phrase, just a theory.

Science, like many of the other subjects that you're learning about in school, has many keywords, and sometimes these keywords are used in everyday life to mean slightly different things, and that can be quite confusing for us.

You might use the word power and energy in everyday life, but when you come into a physics lesson, they mean really specific things.

And knowing about how to use the word in everyday life actually can make it harder for us to understand using the word in a science lesson.

An example of these types of words is the word theory.

A scientific theory is a general explanation that applies to a large number of situations.

Theories are widely accepted by scientists because they have been extensively tested and evidenced.

Now, that's quite different to how we use that word in an everyday context.

You might say, "Oh, I've got a theory that someone's stealing my chocolate." Okay, well, is that a general explanation that applies to a large number of situations? No, not really.

Is that an idea that has been tested and widely accepted and evidenced by lots of scientists? No.

We use the word theory in everyday language to kind of mean, oh, I've got an idea, I've got a hunch, and it's nothing to do with it being evidence-based or backed by scientists.

So just hold that in your mind throughout this lesson.

Use the word theory differently in the way we speak in an everyday language to how we should be using it in a science lesson.

The characteristics of species change over many generations.

This is known as evolution.

Natural selection is a theory that scientists use to explain how and why evolution occurs.

So the theory of evolution by natural selection, which is the full name.

Sometimes you just hear the theory of evolution.

It's actually the theory of evolution by natural selection.

So like all theories, it has lots of supporting evidence, it has been well tested by scientists, it's widely accepted by most scientists, and it applies to a huge number of situations.

Let's look at the keywords in this phrase.

So evolution.

The characteristics of species change over many generations.

There is a lot of fossil evidence for this, and we can see it happening in bacteria and some other animals, for example, peppered moths.

So evolution isn't actually the theory part.

Evolution is a fact.

We can be very, very confident evolution happens, which means the characteristics of species changing over many generations.

Natural selection, that's the theory part.

Organisms that are better adapted to their environment are more likely to survive, reproduce, and pass on their genes to their offspring.

That part is the theory.

So most scientists believe that natural selection is the mechanism which drives evolution.

This process of natural selection is what's causing the characteristics of species to change over many generations.

So evolution, that's a fact.

The characteristics of species change over many generations, that's a scientific fact.

Natural selection, how that happens, that's the part that's a theory.

Okay, let's see if you understood that.

Which of the following are features of a scientific theory? Is it A, well evidenced, B, common sense, C, widely accepted by scientists, or D, well tested? Take five seconds or pause the video if you need a bit more thinking time.

Click play when you're ready to see the answer.

Okay, let's have a look at the answers.

So A, well evidenced, that's a feature of a scientific theory.

C, widely accepted by scientists, that's also a feature of a scientific theory.

And well tested, that's also a feature of a scientific theory.

Well done if you got those right.

Sam is learning about the theory of evolution by natural selection at school.

Sam says the following: "Evolution is just a theory.

That means it's probably not true." Is Sam's understanding correct or not? Explain why.

So you'll need to pause the video now to give yourself enough time to think through that and to write down your answer.

Click play when you're ready to see the answer.

Okay, let's look at the answer.

Sam is not correct.

The word evolution means the characteristics of species change over many generations, which isn't a theory.

It's considered to be a fact because there is an overwhelming amount of fossil evidence and other evidence for it.

For example, we can observe species such as bacteria and even some animals changing over generations.

Natural selection is a theory that scientists use to explain how and why evolution occurs.

And just because natural selection is a theory, it doesn't mean it's probably not true either.

A scientific theory, unlike how we use the word in everyday language, is trustworthy as it has the following features: well tested, well evidenced, applies to a huge number of situations, and widely accepted by most scientists.

So you might have heard it said and you might continue to hear it said, "Oh, it's just a theory, it's just a theory," but have it in your mind that the way we use the word theory in everyday talk, everyday speech is different to how we should use the word in a science lesson.

Well done if you got that right.

We've completed the first part of the lesson.

We've talked about how saying evolution is just a theory isn't quite the correct way of talking about it.

Now we'll look at a really famous example of evolution by natural selection, the evolution of horses.

Evolution is the process in which the characteristics of species change over many generations.

Sometimes species change so much they're classified as new species.

Natural selection can cause the common features of a species to evolve or to change over generations.

Horses are a really well-studied example of evolution by natural selection, and they're a really well-studied example because there's a huge amount of fossil evidence, huge amount of fossils of horses, including many complete fossilised skeletons of early horses like the one I've got on the side of my slide here.

So let's take a closer look at the evolution of horses.

We know from fossil evidence that the early ancestors of the modern horse were very small, around 45 centimetres tall, around the size of a dog.

They ate leaves and they lived in woodland areas.

And over millions of years, their habitat changed to open grassland, so much fewer trees, much more grass.

There was less food available, more grass and far fewer bushes and trees.

Let's see if we're following that so far.

What evidence is there to support the evolution of horses across millions of years? Is it A, fossils of their remains, B, photographic evidence of the extinct species, or C, descriptions by people who were alive at the time? Give yourself five seconds, or if you need more time, pause the video, click play when you're ready to see the answer.

Okay, let's look at the answer.

It is A, fossils of their remains.

So there is no photographic evidence of the extinct species.

They existed millions of years ago, so no photos, and no descriptions by people who were alive at the time.

This happened across millions of years.

Modern humans have only been around for about 350,000 years, so not around to take photos or to write down descriptions of what they were like.

Well done if you got that right.

We can see through the fossil records that horses have evolved over millions of years.

This is particularly noticeable in their skulls, teeth, legs, and toes.

So we'll start here with an early ancestor of the modern horse from about 55 million years ago.

This has got a very small skull, very small teeth, and very short leg bones and it's got four toes.

So over time, you can see the skull's getting bigger, the teeth are getting larger.

And now in this version of an early horse there is only one toe, which is very similar to a modern horse.

We've got a much bigger skull, much larger teeth, and now a much longer leg bone stood upon one toe.

And here we have the skull of a modern horse, the teeth of a modern horse, and the leg bones of a modern horse.

Okay, let's check to see if you understood that.

Modern horses have long teeth for chewing grass, long leg bones, and one toe.

They evolved from a small forest dwelling species that had a short teeth for chewing leaves, four toes, and short leg bones.

Put these groups of fossils in the correct order to show the evolution of the modern horse.

Take five seconds or pause the video if you need more time.

Click play when you're ready to see the answer.

Okay, let's have a look at the answer.

Well done if you got those in the correct order.

So you can see the first set of fossils have a very, very small skull, very short teeth, very short legs, and four toes, all the way to the fossils, well, the skeleton of a modern horse.

A much bigger skull, much longer and larger teeth, much longer leg bones supported only on one toe.

Well done if you got that right.

Natural election explains how horses evolved.

Let's look at that in some detail.

So first we had variation.

There was variation among the horses' early ancestors.

Some happened to have features that meant that they could eat grass more easily and travel further distances to find food.

Now remember, the habitat of the horse has changed over millions of years.

They used to live in forests, in grassy woodland areas and eat leaves, and so there would have been lots of trees and lots of bushes around for them to eat.

They needed much shorter teeth to do this than you would need for eating grass.

When you're in open grassland as well, animals need to travel much further to get fresh grass to find new food sources.

Okay, so some happened, some of these early horses that were adapted to living in this forest environment, some of them happened, just randomly happened to have features that meant that they could eat grass more easily and travel further distances to find food.

So these features included, so having longer legs and fewer toes, which helped them travel longer distances on the firmer ground, and they had larger teeth, which were better suited to eating grass.

Remember, these are changes that happened over millions of years, okay? So, that leads to an advantage.

These horses now had an advantage over the other early horses, as they could get more food.

So, competition.

The horses that had these other adaptations for open grassland, they more successfully competed for the limited food available in their environment.

They were better at eating grass than the other early horses were, which were adapted for eating leaves.

So this made these horses more likely to survive and more likely to reproduce, to have offspring.

And then over many generations, again, this happened over millions of years, the features that helped horses eat grass and travel across open plains became more common and slowly they evolved into modern horses.

So, we start off here with this dog-like mammal and we slowly, over millions of years, have the horse evolving into the modern horse.

Okay, let's see if you understood that.

The early horse's environment changed.

This caused the early horse to adapt itself to survive.

Is that true or false? Take five seconds or pause the video if you need some more time.

Click play when you're ready to see the answer.

That is false.

Let's justify the answer though.

Why is it false? Is it false because there was variation among the horses, some happened to have adaptations suited for the new environment, or B, the horses adapted themselves before the environment changed? Take another five seconds or pause the video if you want a bit more time.

Click play when you're ready to see the answer.

Okay, let's take a look.

The answer is A, there was variation among the horses, some happened to have adaptations suited for the new environment.

Well done if you got that right.

This is the second practise task of today's lesson.

The Eohippus is a small forest dwelling ancestor of the modern horse.

Number one, what evidence is there to support the theory that the modern horse evolved from the Eohippus? Number two, describe how the modern horse evolved from the Eohippus.

You'll need to pause a video to give yourself enough time to think about the question and to write down your answer.

Click play when you're ready to see the answers.

Okay, let's take a look at the answers.

So number one, what evidence is there to support the theory that the modern horse evolved from the Eohippus? There is lots of fossil evidence for the ancestral species of the modern horse.

This includes fossilised skulls, teeth, and leg bones.

Let's look at number two.

Describe how the modern horse evolved from the Eohippus.

There was variation among the early horses.

Some happened to have features that meant they could eat more grass and travel longer distances to find food.

These features included: longer legs and fewer toes, which helped them travel longer distances on firmer ground, and larger teeth, which were better suited to eating grass.

These horses now had an advantage over the other early horses as they could get more food.

They more successfully competed for food.

This made them more likely to survive, reproduce, and pass on their genes.

And over many generations, the features that helped horses to eat grass more easily and travel across open plains became more common and they slowly, over millions of years, evolved into modern horses.

Well done if you got that right.

We are onto the final part of today's lesson.

We've talked about why saying just a theory about the theory of evolution by natural selection isn't quite right.

We've also discussed a really key example of evolution by natural selection, the evolution of the horse, and now we're gonna talk about misconceptions that some people have about evolution.

Misconceptions are views that are incorrect because they are based on not fully understanding an idea.

There's no need to be embarrassed or to make fun of someone for having a misconception.

We are all full of misconceptions about one thing or another.

Let's have a look at the word misconception.

So that prefix mis, that means false or wrong, and conception, that's to do with the idea.

So having a false or a wrong idea about something.

There are many common misconceptions about the theory of evolution by natural selection.

Again, there's no need to feel bad about it.

Let's just acknowledge it and learn from it.

One really common misconception is that evolutionary biologists, so people that study evolution, believe that humans are descended from apes.

This is not what evolutionary biologists believe.

It's not what they think.

They believe that humans share a common ancestor with apes and that this ancestor existed millions of years ago.

They believe this because the evidence available points to this, including the fact that humans have about 99% of their DNA in common with chimpanzees.

So having a common ancestor is not the same as being descended from something.

That's a really important distinction.

Okay, let's see if we understood that.

Humans evolved from chimpanzees.

Is that true or is that false? Take five seconds or pause the video if you want more time.

Click play when you're ready to see the answer.

That is false, but why is it false? Let's justify that answer.

Is it false because chimpanzees and humans have no DNA in common with each other, or is it false because chimpanzees and humans have a common ancestor? Take five seconds, pause the video if you want some more time.

Click play when you're ready to see the answer.

It is false because chimpanzees and humans have a common ancestor.

Humans didn't evolve from chimpanzees.

They do have DNA in common, so that's why A is wrong.

They have about 99% of their DNA in common.

But the reason it's false is because chimpanzees and humans have a common ancestor, not one being derived from another.

Well done if you got that right.

Another common misconception is that an organism chooses to change in order to adapt to an environment.

If you think about that for any length of time, you'll see that doesn't really make sense.

If I wanna be taller to be better at basketball, I can't just make myself taller.

That's not how it works, unfortunately.

Stuff like height is controlled largely by our genetics, yeah? So if we take the example of early horses, they didn't choose to change their teeth when different food became available.

Horses that happened to have larger teeth were better suited to the new environmental conditions, so they were more likely to survive, reproduce, and pass on their genes.

We can see that in the diagrams of the fossils here below.

Okay, hopefully that made sense.

Which of these statements finishes off the following sentence? The early horses environment changed so, A, they decided to change and become better adapted to their environment, B, some early horses happened to be better adapted to their new environment, or C, they learnt how to become better adapted to the environment from the other horses? Take five seconds, or if you want more time, click pause, then click play when you're ready to see the answer.

It was B.

Some early horses happened to be better, so randomly they happened to be better adapted to their new environment.

You can't change and decide to become better adapted to the place you live.

You can't change your genetics that way.

This is something that happens randomly in nature and it's because of the variation between members of a species.

Another misconception is that organisms are intending or they're trying to change in order to adapt to their environment.

So they're really thinking through like, "Okay, I should be red, 'cause that will make me camouflaged." There's not that thought process going on.

Evolution is a random process, and mutations, which are changes in DNA, are constantly occurring and cause variation among individuals of a species.

If we have a look at my flowers, we've got two different colours of the same species of flower, and they're different just due to changes in their DNA, mutations, differences in their DNA.

It might become useful at some point.

Maybe a bee will come along that will have a preference for a specific colour of this geranium flower, but we don't know if that's gonna happen.

This variation is there, and then sometimes it becomes useful and sometimes it's not useful.

When conditions change, that's when some of these mutations can be considered useful.

The last example of a misconception about evolution that we're gonna talk about is the idea that an organism changing over the course of its lifetime is an example of evolution.

So evolution is a process that happens over many generations, often over hundreds of thousands of years.

Choices organisms make or damage they accumulate are not examples of evolution.

So here are some examples which are all not examples of evolution.

So an animal learning to hunt from its parents isn't an example of evolution, nor is getting a scar caused by an injury or maybe surgery, or gaining lots of muscle from exercising.

That's also not an example of evolution.

These are all changes that happen in the course of an organism's lifetime.

They're not changes that happen over many generations or hundreds of thousands of years.

Okay, let's see if we understood that.

Which of the following statements could be examples of evolution by natural selection? Is it A, after chasing lots of prey, a predator's leg muscles got bigger and it can run faster, B, a baby inherits a useful characteristic from its parents, C, in each new generation of roses, the petals are bigger and redder, which attracts more pollinators, D, species dies out because of climate change, E, the average beak length of a population of birds increases over many generations? You can take five seconds now, or if you want some more thinking time, pause the video, click play when you're ready to see the answers.

Okay, let's look at the answers.

Was it A, after chasing lots of prey, a predator's leg muscles get bigger and it can run faster? No, unfortunately not.

That's a change that occurs in an individual's lifetime.

That's not evolution.

A baby inherits a useful characteristic from its parents? That's also not evolution.

In each new generation of roses, the petals are bigger and redder, which attracts more pollinators.

This could be an example of evolution by natural selection.

There's a chance it could also be the person that's breeding the flowers who's directing this.

So it might not be, but it could be an example of evolution by natural selection.

A species dies out because of climate change.

Is that an example? No, that's an example of extinction.

And finally, the average beak length of a population of birds increases over many generations.

That could also be an example of evolution by natural selection.

Well done if you got that right.

This is our final practise task for today's lesson.

This article is taken from a news website.

"Crickets are insects that make a 'singing' noise by rubbing their wings together.

The noise can often be heard on warm summer nights.

However, in 2003 scientists on a Hawaiian island found a few crickets that were no longer able to 'sing.

' This was due to a change in the crickets' DNA, which changed the shape of their wings.

The scientists think that not 'singing' helped these few crickets to avoid predators.

Perhaps they lived to die of old age, which for a cricket happens after only a few months! Ten years later, most of the crickets on the island were unable to 'sing.

' Silence had fallen!" Okay, we've got some opinions about this.

Alex thinks, "It was clever of the crickets to stop 'singing.

' It helped them to survive." Jacob thinks, "The crickets evolved so that they could avoid getting eaten by predators." Laura thinks, "When 'singing' crickets saw that silent crickets had an advantage, they also stopped 'singing.

'" And Andeep thinks, "It was a random chance that the change in the crickets' DNA first appeared.

It's just coincidence that it was helpful." Decide whether each student's understanding is correct or incorrect.

Explain your answers.

So you need to pause the video now to think about your answer.

Click play when you're ready to see the answers.

Good luck, everyone.

Okay, let's check our answers.

Alex is incorrect.

The crickets didn't think through their choices and choose to stop singing.

Jacob is also incorrect.

Organisms can't deliberately decide to evolve to solve a problem.

Laura is incorrect.

The crickets didn't learn to stop singing from one another.

The article says it was due to a change in their DNA.

Andeep is correct.

Evolution is a random process.

When conditions change, certain features in organisms become helpful or unhelpful, and natural selection is the process in which these helpful features often become more common.

Well done if you got that right.

Well done on completing today's lesson.

Let's summarise what we learnt to help it stay in our memories.

Evolution by natural selection is a scientific theory which explains how the characteristics of species change over many generations.

The evolution of the horse is a very well researched and well-known example of evolution by natural selection.

Species do not choose to evolve.

They happen to have adaptations which help them survive, and these become more common in later generations due to natural selection.

Evolution is the process by which the characteristics of species change over many generations, not an individual changing during its own lifetime.

Great work on today's lesson.

I really hope you enjoyed it and I hope to see you back again soon for our next lesson.