Lesson video

Welcome to today's lesson from the Oak National Academy.

Today's lesson is taken from the unit adaptations, competition, natural selection, and evolution.

And today's lesson title is "natural selection." Hi, I'm Mrs. Wheat and I'll be taking you for today's lesson.

By the end of today's lesson, you'll be able to explain how variation and competition lead to the natural selection of individuals with the most helpful characteristics.

Let's have a look at our keywords.

Today's lesson has got five keywords, variation, competition, fittest, reproduction, and natural selection.

Before I show you the definitions, I just wanna reassure you, you don't need to try and memorise all of these now.

Take your time.

I'll be quiet for five seconds, but if you wanna pause the video to give yourself some extra time, feel free to read them through really slowly or to copy them down if you want.

So here are our definitions.

Today's lesson is in two parts.

First of all, we'll talk about natural selection, the process of it, what it is, what it means, and then in the second half of today's lesson, we'll look at a really, really common example of natural selection and the human impacts on natural selection.

But first of all, natural selection.

All living organisms have features that help them to survive and reproduce in the places they live.

And these features are called adaptations.

So if we look at my three examples down here, I've got three species of birds.

I've got a kingfisher who's eating a fish, I've got a black bird eating a berry, and I've got a hummingbird who's trying to reach their beak inside the flower to get the nectar at the base of the flower.

So they're all birds, they've got lots of things in common, they've got wings, you know, they've got feathers, they all have beaks.

And the beaks are slightly different depending on the food they're trying to eat.

These birds are highly adapted, highly specialised to be able to get the food they want.

If we take just the hummingbird for example, it's got a much longer and thinner beak than the other two examples, and that's because it needs to reach inside these quite narrow flowers in order to get the nectar.

So that's an example of an adaptation that the hummingbird has and how it's adapted in order to, yes, in order to survive, in order to reproduce, it needs to get more food to do those things.

So these adaptations are a result of a process called natural selection, which we're gonna talk about this whole lesson.

Because of variation within a species, some individuals have adaptations that others do not.

These adaptations can help them to compete for resources, so like food or mates or shelter if we're talking about animals and it helps 'em to survive and reproduce as well.

So if we look at this example of the deer here.

We've got two stags who are fighting.

So we've got deer with larger antlers are more likely to survive and reproduce.

And that's because the way that a herd of deer works is that you have one kind of alpha male who is dominant over a large group of female deer, doe's and male deer, stags, will fight for control over this group.

As you can see here, they're fighting with their antlers.

So that's why the stags have got the larger antlers are more likely to be successful when they fight each other, when they're competing for mates for the females.

And that then means they're more likely to reproduce.

So helpful adaptations tend to become more common in a species due to a process called natural selection.

Let's talk about that in detail.

So now I'm gonna talk you through the whole process of natural selection and this slide is gonna be a summary of that.

We can break natural selection down into about six steps.

And don't worry if you don't feel like, oh, I don't 100% understand it yet at the end of this slide, we're gonna spend the rest of the lesson going through natural selection in a couple of different contexts, and that's gonna really help your understanding.

So the process of natural selection involves the following steps.

First, we've got variation.

So due to random chance, some individuals of a species have different traits, characteristics.

If we look at the deer, some of those deer, some of those stags had bigger antlers than other stags and that just happened randomly.

Advantage, some traits can give individuals an advantage.

So as we said, the stags that had large antlers, that was really useful for them for competition.

That's an advantage.

This advantage allows 'em to compete successfully.

So the stags were fighting and the ones with larger antlers are then more likely to win the fight to compete successfully.

That makes them more likely to survive.

Unfortunately, sometimes when animals do fight with each other over food, over mates, over territory, they do die.

So again, the ones with larger antlers that serve them well and they're more likely to survive.

Reproduction, that means that they're more likely to survive and then have offspring afterwards.

You can't have offspring if you died, obviously.

And so the final step is inheritance.

So because this organism has survived, it's reproduced, it's then more likely to pass on its traits.

So say the big antlers to their offspring, offspring like children.

Over generations, this traits becomes more common.

And this is in a nutshell how natural selection works.

You might have noticed that it says more likely and that kind of thing.

It doesn't say this is definitely what happens every single time.

This is a random process and there's so many different variables in nature that can control or change the way things are.

So this is a description of what happens a lot of the time, most of the time, it's not what happens in every single situation, but on the balance of probabilities, this is what happens kind of most of the time.

Most of the time the organism that is best adapted is the one that's more likely to survive, reproduce, and pass on its genes to its offspring.

Okay, let's see if we understood that.

Complete the sentences about natural selection.

Use the words from the list.

Offspring, reproduce, compete, variation.

There are differences in the traits of individuals of a species.

This is called blank.

Some of these differences give individuals an advantage over each other.

This makes them more likely to blank successfully for resources.

They are then more likely to survive blank and pass on their traits to their blank.

So you can have five seconds now, or if you need a bit more time than that, feel free to pause the video.

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

Okay, how did you do? Let's have a look.

There are differences in the traits of individuals of a species.

This is called variation.

Some of these differences give individuals an advantage over each other.

This makes them more likely to compete successfully for resources.

They are then more likely to survive, reproduce, and pass on their traits to their offspring.

Well done if you got that right.

So that was a brief overview of the process of natural selection.

Now we're gonna put it into a different context, hopefully you are all familiar with giraffes.

So evidence suggests that giraffes have not always looked the way they do now.

Their ancestors were similar to deer.

Scientists believed that the traits of these ancestors changed over many generations by natural selection eventually forming the modern day giraffe.

So that's look at how natural selection led to the modern day giraffe.

So first we have variation.

The ancestors of giraffes had different neck lengths, some shorter and some longer than others.

This is an example of variation so differences within a species.

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

Some giraffes had short necks, others had long necks.

Select the reason why.

Is it A, some giraffes stretched their necks further to get food.

B, variation caused by random chance or C, some giraffes were stronger than others.

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

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

Let's have a look at the answer.

It is B, variation caused by random chance.

So you might have thought it was A, some giraffes stretched their further to get more food.

In natural selection, we're talking about traits that are passed on from parent to offspring.

Something that you do during a lifetime, like going the gym and getting really big muscles doesn't get passed on to your offspring.

If I go to the gym tonnes, I'm not gonna give birth to a baby that has huge muscles.

Unfortunately isn't how it works.

You might have thought it was C, some giraffes are stronger than others.

We can kind of get fixated on this idea when we talk about natural selection or survival of the fittest, that it's the big strong animals who survive.

But not every animal, not every plant is big and strong.

There's lots of different ways you can be adapted and you could be considered the fittest organism in your species.

It's not just about being strong, it is not just about fighting like the stag example.

In this example, the giraffes that were the best adapted weren't the strongest, they had longer necks.

Okay, let's keep going.

So we've looked at variation, which is the first step of natural selection.

Now we're onto the next step, adaptation and competition.

So having a longer neck is an advantage as it helps the individual reach leaves higher up on the tree.

The individuals with longer necks were better adapted to their environments so were the fittest.

Now that word fittest isn't necessarily to do with physical attraction, it isn't necessarily to do with stamina or physical strength it's about being the best adapted to the environment.

So if we look at my example of the giraffes here, I've got in the photo, I've got in the picture rather.

We've got one giraffe who's got a slightly longer neck.

They're getting more food.

Obviously that's a huge advantage.

We've got the guy on the other side, much shorter neck not getting as much food.

It's not gonna go well for the one with a short neck unfortunately.

So this adaptation, having the long neck allowed them to compete successfully for foods.

Long neck is getting much more food.

Short neck looks a bit sad and a bit hungry.

The individuals with shorter necks competed less successfully as they couldn't reach the leaves higher on the tree.

It's very sad.

Okay, let's see if we understood that part.

Giraffes are in competition with each other for food and the winners will be decided at random.

Is that true or is that false? Take five seconds or pause the video.

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

That is false.

Okay, but why is it false? Let's justify the answer.

Is it false because the biggest and strongest giraffes will be successful? Or is it because the best adapted giraffes will be successful? Take five seconds or pause the video.

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

It is the best adapted giraffes that will be successful.

Again, we can get really obsessed and really into this idea that it's about being big and strong.

Don't always need to be big and strong to have the advantage in nature.

Sometimes being really small is helpful 'cause you can hide.

So being best adapted can look very different depending on the organism.

Okay, let's continue.

So we talked about the first part of natural selection.

We've had variation and then we've had that's created an advantage, that then advantage is useful in a competition.

And now we're gonna talk about the last part of natural selection, which is survival, reproduction, and inheritance.

So the individuals with longer necks were more likely to survive.

Again, it doesn't happen like this every single time.

It might be for example, that the giraffe with a longer neck had a disease or got eaten by a predator and so they don't end up surviving and they don't pass on their genes.

We're talking about this happening on a huge scale over a whole species.

Yeah, so this is what would happen most of the time.

So the individual with the longer neck were more likely to survive and reproduce, to produce long necked offspring.

As the shorter neck giraffes produced fewer offspring because they were less likely to survive because they weren't getting as much food more of the next generation of giraffes were long necked.

This repeated over many generations and eventually the long-necked trait was common to all giraffes.

So that's a really key part that again, lots of people leave out.

This isn't just kind of someone passing something onto the offspring and that's it.

That's not natural selection.

Natural selection is when this is repeated over many generations and these traits become common across a whole species.

Okay.

Right, let's see if you understood that part.

The fittest individual in a species will A, always survive and reproduce.

B, is more likely to survive and reproduce.

C, is no more likely to survive and reproduce than the other members of the species.

D, is less likely to survive and reproduce.

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 look at the answer.

It is B, is more likely to survive and reproduce.

Well done if you got that right.

This is our first practise task for the lesson.

Parus major is a species of bird.

We've got them here on the bird feeder.

In the UK, this species of bird often gets its food from bird feeders in people's gardens.

The birds with longer beaks are able to get more food from the bird feeders.

Scientists have observed that the longer beaks are becoming more common in the Parus major population in the UK.

Explain the scientists observation using the following ideas.

So mention in your answer, variation, adaptation, competition, and natural selection.

So you'll need to pause the video now.

Make sure you read through the question really carefully.

Give yourself enough time to think about it and write your answer.

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

Good luck.

Let's see how you did.

So explain the scientist observations.

There was variation in the Parus major population, which arose at random.

Some of the birds had shorter beaks and some of them had longer beaks.

Individual birds with longer beaks had an advantage in the competition for food as they were better adapted to reach food from inside the bird feeder.

These individuals were more likely to survive and reproduce.

That's natural selection and were therefore more likely to pass on the longer beak shape.

Over a number of generations, as the birds reproduced, the longer beak shape became more common in the population.

Really great job if you got that right.

Right, we've gone through and defined the process of natural selection and now we're gonna look at a really famous example of natural selection and the human impact on natural selection.

If the environmental conditions in a species habitat change, some individuals that were previously well adapted might now be less well adapted to survive there.

If we look at my photo of the cactus, you probably know cactus aren't really designed for snow.

They're well adapted for dry, hot environments.

If then the habitat changes, the climate of the habitat changes, they're not gonna do very well.

They've got all of these really, really, really high specialised adaptations to survive in hot dry climates.

So some individuals that were previously poorly adapted on the other hand, might now be better adapted.

So it might be a plant that wasn't doing too well and does it but now there's snow, the adaptations they happen to have, or the features they happen to have are now super useful for existing in snow.

So this has impacts on natural selection and we'll have a look at an example of that.

Human actions can cause environmental conditions to change too.

So our example is the peppered moths.

Peppered moths are found in the United Kingdom and it can be found in a range of colours.

So here we have a light coloured peppered moth, and then we have a dark coloured peppered moth.

So they're the same species, but they just come in a variety of colours.

That's the variation.

Before the 1800s, the most common form of the moth was white with speckles.

So that's like the picture on the top.

In the 1800s, moth collectors, so some people collect moths and insects and butterflies for fun.

It's not a super common hobby nowadays, but it was more common in the Victorian era.

So in the 1800s, moth collectors noticed that the rare dark coloured moths were becoming more common.

We need a little bit more context to what was happening during this time period and then we'll start talking about natural selection.

So during this time, humans were burning huge amounts of coal as a fuel to provide energy during the industrial revolution in the 1800s.

Maybe you've studied that in history.

So here in my picture, we've got lots of air pollution coming out of a factory.

The pollution from the coal killed the pale lichen growing on trees.

So lichen is a group of organisms that grow on the bark of trees.

So if we have a look at my picture on the bottom half of the screen, that's some lichen growing on a tree, growing on tree bark.

So this in combination with the soot from the coal led to darker coloured tree trunks.

Maybe you can see where this is going already.

So due to the change in tree trunk colour, darker moths were now better camouflaged.

If we have a look at my photo, the darker moth is much harder to see than the lighter moth.

This meant that predators found it harder to hunt them, so they were less likely to be eaten and more likely to survive and reproduce.

Dark moths passed on this trait to their offspring and dark coloration became more common in each new generation of moths.

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

Some moths were light-colored, others were darker.

So select the statement that could correctly finish this sentence.

So is it due to A, pollution from coal burning factories? B, some moths changed colour to hide from predators or C, variation caused by random chance.

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

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

Okay, let's check our answers.

So some moths were light-colored, others were darker.

This is due to variation caused by random chance.

Well done if you got that right.

So using our six steps from earlier, let's sum up what happened to the moths.

The moths went through natural selection.

So the first stage of natural selection, do you remember what that was? That was variation.

There was variation among the moths.

Some were light-colored, others were dark.

What's the next step of natural selection? It is advantage, the darker moths are better camouflaged.

What comes next? Competition.

Darker moths were less likely to be eaten by predators.

They were harder to see.

Okay, what's after that? Survival.

This made the darker moths more likely to survive.

What comes next? Reproduction.

So the darker moths more likely to survive, more likely to have offspring and inheritance.

So they were more like to survive, more likely to reproduce and then more likely to pass on this dark coloration trait to their offsprings and over generations this trait became more and more common.

Really great job of this lesson so far.

Let's check what we learned and then have another practise task.

The dark-colored moths were fittest and became more common over time.

This is an example of.

Is it, A variation, B, natural selection or C competition? Take five seconds or click pause if you need a bit more time.

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

Okay, it is B, natural selection.

Well done if you got that right.

So this is our final practise task for today's lesson.

It is also a bit more history about these moths.

So in 1956, the Clean Air Act was passed by the United Kingdom's parliament.

This along with other measures reduced air pollution in the UK.

The reduction of soot from coal and lichen regrowing, Remember that's that group of organism that grows on the bark of trees.

It caused the bark on the trees to become lighter.

And we can see that from my photo.

The previous diagram had dark-colored bark.

We've got a lighter coloured bark now.

Suggest what happened to the population of light-colored moths and dark-colored moths now that the bark's changed.

Explain your answer.

So think about all the ideas we've talked about in terms of natural selection.

Think about all the keywords that we've used when describing natural selection in all the stages.

And you'll need to pause the video now to give yourself enough time to think about all that and to put it down on the page.

Right, good luck.

Let's go through your answer.

Suggest what happened to the population of light-colored moths and dark-colored moths.

Explain your answer.

The population of dark-colored moths decreased and the population of light-colored moths increased.

This is because the dark-colored moths were no longer camouflaged, but now the light-colored moths was camouflaged.

The light-colored moths were less likely to be eaten by predators.

The dark-colored moths were more likely to be eaten by predators.

More of the light-colored moths survived and reproduced and passed on the light-colored trait to their offspring.

Fewer darker-colored moths survived, reproduced and passed on their dark-colored trait to their offspring.

This repeated over generations until the majority of the population were light in colour.

Really great job of you got that right.

And that's today's lesson.

Really great job today.

Let's go through the steps of natural selection one more time to help it really stay in your memories.

The process of natural selection involves the following steps.

One, variation.

Due to random chance, some individuals of a species have different traits or characteristics.

Two, advantage.

Some traits can give individuals an advantage.

Three, competition.

This advantage allows them to compete successfully.

Four, survival.

This makes them more likely to survive.

Number five, reproduction and more likely to have offspring.

And finally, step six.

Inheritance and more likely to pass on their traits to their offspring.

Over generations, the trait becomes more common.

Really hope you enjoyed today's lesson today.

Well done in all your hard work.

Take a bit of a break now and I'll see you back really soon for our next lesson.