Lesson video

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

This lesson is taken from the unit fossil evidence, selective breeding and expanding evolution.

And the title of today's lesson is The Evolution of New Species.

Hiya, I'm Mrs. Wheate, and I'm gonna be your teacher for today's lesson.

By the end of today's lesson, you'll be able to explain how natural selection can lead to the evolution of new species.

Let's have a look at our keywords.

So we've got four keywords for today's lesson.

Species, a group of similar organisms that can reproduce and produce fertile offspring.

Speciation, where natural selection causes new species to form.

Natural selection.

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

And adaptation, a feature that organisms have that helps them live in a particular place and survive.

So no worries if you haven't memorised all of that.

I've already read it out once.

If you want some more time, I'll be quiet for five seconds.

You can read them through again, but if you want a bit more time, you can click pause and read them through really slowly or write them down.

Today's lesson is in two parts.

We're first of all gonna talk about speciation, which is how new species evolve.

And then we're gonna look at a specific example of speciation, which are the Galapagos tortoises.

But first of all, what is speciation? Let's start by defining a species.

A species is a group of similar organisms that can reproduce and produce fertile offspring.

No one is certain how many species there are on the planet, but scientists suspect there are millions.

I have chosen six to try and get across some of the huge breadth we have and the differences between species.

We've got a species of mushroom called fly agaric.

We've got a species of birds, the blue peacock, a species of moth, Polyphemus moth, a species of plant called the Venus flytrap.

We've got a moon jellyfish and we've got a species of monkey called the Emperor tamarin, which I think have really, really fantastic moustaches.

So each of these individuals can only reproduce and create fertile offspring with another member of their species.

So if we want emperor tamarin babies and grand babies, then emperor tamarins need to reproduce with emperor tamarinds.

Same for the mushrooms, same for the peacock, same for the moss, same for the plants.

So let's see if you understood that.

Lions and tigers can breed and produce infertile offspring called ligers.

True or false? Lions and tigers are the same species because they can produce offspring.

Is that true or is that false? Take five seconds or click pause if you want some more thinking time, click play when you're ready to see the answer.

Okay, it is false, But why is it false? Let's justify that answer.

Is it false because A, producing offspring is not a feature of organisms of a species, or B, organisms need to produce fertile offspring in order to be considered the same species.

Take five seconds or click pause if you want more thinking time.

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

It is B.

Organisms need to produce fertile offspring in order to be considered the same species.

Well done if you got those right.

Evolutionary biologists think that all the species on the planet descended from a single common ancestor millions of years ago.

They think that very slowly over time, organisms develop traits that led them to be better adapted to their environment.

Eventually, the features of a group of organisms can become so different that they can be classified as different species.

So let's talk about speciation and how that works.

New species are formed in the process of speciation, but to understand speciation, we need to understand natural selection because speciation occurs as a result of natural selection.

So let's go through the process of natural selection, how it works, what it involves.

So first of all, the first stage of natural selection, there needs to be variation in a population.

So due to random chance, some individuals of a species have different traits, so different number of seeds in plants, or different eye colour or hair texture in human beings, for example.

So some traits are adaptations.

They're features that give organisms some help in the area that they live in and help them to to survive.

These adaptations can give individuals an advantage.

So all organisms are in competition, whether they realise it or not, for finite resources.

So resources for plants include things like sunlight and water and minerals and space.

Resources for animals include things like mates and territory.

So having adaptations that are an advantage help individuals to complete successfully for these finite resources.

So organisms that have these adaptations and can compete successfully are much more likely to survive.

And they're also much more likely to survive until reproduction age and then have offspring.

So then these offspring are again, more likely to pass.

Oh, sorry.

No.

So these organisms that are really well adapted, have an advantage, compete successfully, have survived and reproduce, they're more likely to pass on these adaptive traits to the offspring.

And over generations, these traits become more and more common or can become more and more common.

And sometimes this process happens over and over and over again.

And the features of a group of organisms can change so much that we can classify them as a new species.

So this whole process, and then at the end of it becoming so different that the two groups of organisms of two populations of organisms can no longer reproduce and produce fertile offspring.

That's speciation.

Let's see if you understood that.

Put these same in order to describe the process of natural selection.

A, some traits can give individuals an advantage, and this allows 'em to compete successfully.

B, they're more likely to pass on their traits to their offspring.

Over generation, the traits become more common.

C, sometimes the features of a group of organisms can change so much that we classify them as a new species.

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

E, this makes them more likely to survive and have offspring.

Take five seconds, or if you want more time, pause the video, click play when you're ready to see the answer.

Okay, let's see the answers.

So first we have D.

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

The next step is A, some traits can give individuals an advantage, and this allows 'em to compete successfully.

Next is E.

This makes them more likely to survive and have offspring.

B, they're more likely to pass on their traits to the offspring.

Over generation, the traits become more common.

And finally, C.

Sometimes the features of a group of organisms can change so much that we classify them as a new species.

Well done if you got that right.

Speciation often occurs because groups of organisms become separated by a geographical barrier, such as a mountain range or a body of water like a river.

So when populations are separate like this, so we have the same species of animal and they're separated by a mountain, a mountain range, we've got one on one side, one on another.

So they are now reproductively isolated, which means that because of the geographical barrier in between them, they can't reach each other to mate.

So let's look at some examples of that.

Tigers and snow leopards are both species of big cat native to the Indian subcontinent.

Scientists think that they evolve from the same common ancestor roughly 3 million years ago.

So we've got the tiger and we've got the snow leopard.

They've definitely got features in common and they're both cats, but the markings are completely different.

You can see from the photos that live in completely different habitats.

So what happened? How did they start off as the same species and then three millennias ago, they diverged and became two completely separate species.

So as the common ancestor has not been discovered, we're gonna call that common ancestor species A.

Although they're closely related, they have specific adaptations that help them to survive in their different habitats like you can see.

So at some point, species A split into different populations.

So here we've got a map of India and some of the Indian subcontinent, and we've got species A living somewhere there.

So some began living at high altitudes in the Himalayas, a really famous mountain range in India and other countries like Pakistan nearby.

Others moved to areas that were more like a rainforest and a grassland type environment.

Mountain ranges such as the Himalayas are a geographical barrier that separate populations, making them reproductively isolated.

So each population evolved differently due to the different conditions in each habitat.

So they evolved differently because there's variation within populations.

So we had the same kind of ancestral population, species A that got separated 'cause some migrated to a mountain range, and then some migrated to rainforest or grassland type areas.

So really different conditions.

Natural selection causes traits that help organisms to survive and reproduce in their specific environment to become more common over generations.

So natural selection is happening in these, in these two populations and the population that lives in the Himalayas, which is really called really mountain environment.

Different traits are an advantage there than the population that's living in a rainforest or a grassland.

We need very, very different traits there to be successful.

So natural selection is work in these two different populations.

And natural selection is kind of shaping how these organisms evolve.

Eventually, the population become so different from each other that they could no longer interbreed and create fertile offspring if you kind of brought 'em together and encouraged them to mate.

So at this point, we consider them different species.

Let's see if you understood that.

Which of the following statements is true? A, geographical barriers can lead to speciation.

B, Speciation occurs so that organisms can overcome geographical barriers, or C, geographical barriers have no effect on new species being formed.

Take five seconds or click pause if you want more time, click play when you're ready to the answer.

It is A, geographical barriers can lead to speciation.

Great job if you got that right.

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

Answer the question and complete the task below.

Laura is learning about speciation at school.

She says, evolutionary biologists believe that all the species on the planet are the same as they have always been.

Is she correct? Explain why or why not.

And number two, explain what is meant by speciation and how geographic separation can cause it to recur.

So you need to pause every day now to give yourself enough thinking time.

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

Okay, let's go through the answers.

So is she correct? Explain why or why not.

Laura is incorrect.

Evolutionary biologists think that all the species on earth have descended from the same common ancestor and evolved into the species that are currently alive.

Number two, explain what is meant by speciation and how geographic separation can cause it to occur.

Speciation is the process in which natural selection causes new species to form.

Geographic separation by a river or mountain range can cause populations of species to be in different environments.

These different environments lead to different adaptations in the species as natural selection causes organisms to be well adapted to their environment 'cause they're better able to survive and reproduce.

Eventually the populations can become so different that they cannot mate with each other and a different species.

Really great job if you got that right.

Okay.

We have talked about what speciation is and one example of how it occurs.

Now we're gonna look at another example in a lot of detail, the Galapagos tortoises.

So the Galapagos Islands are a group of islands roughly 500 miles west of mainland, South America.

And they're now really famous.

But there are many species of plants and animals that exist nowhere else in the world.

These islands played an important role in the development of the theory of evolution by natural selection.

Charles Darwin, who is really famous for his contribution to the development of the theory of evolution by natural selection, spent five weeks there whilst on his voyage around South America searching for evidence to explain how evolution occurs.

Darwin noticed that the animals of the Galapagos Islands are really different from each other, even though the islands are relatively close together.

Some of them are around like 50 miles apart from each other.

So in terms of scope of the whole planet, 50 miles, not that big a distance.

He compared this two mainland South America, which is a huge area, thousands, thousands of miles across, which, but there's much less variation in species in parts of South America, even though it's a way bigger area.

So in the Galapagos you have, for example, a species of bird which is located just on one island, a species of Mockingbird, for example.

And then 50 miles away from it, you have a completely different species of bird, similar, but different enough that they're different species.

He didn't find that in South America.

So across huge stretches of hundreds and hundreds of miles, you might have the same species distributed pretty evenly across this area.

So he really wants to know why that was.

So one example of this that has now been really well studied is the Galapagos tortoise.

So they're a group of very closely related species of tortoise.

They played an important role in the development of the theory of evolution by natural selection.

So they're a key example of a group of animals that have different features depending on which Galapagos island they live on.

And species of Galapagos tortoise can broadly be put into two groups based on their features.

So you've got tortoises with a saddle-shaped shells, so you'll understand what I mean.

Let's compare it to the other one.

So I'd say this is more of a classic tortoise shape, the dome-shaped tortoise shell.

So dome-shaped tortoise like dome, that kind of curve shaped, pretty standard tortoise shaped.

And then you have a saddleback tortoise, which looks really, really different.

And so you can see that the front of itself kind of rises up like a saddle that you would put on a horse.

And so they look really, really different.

And there's a really important reason as to why they look so different.

So islands with dryer climates have less vegetation on the ground.

The tortoises that live on these islands have to stretch their necks up to bushes and for tree cactuses for food, they have saddle-shaped shells, which is an adaptation that allows 'em to reach food from higher up.

So you can see in the pictures actually on the saddle back tortoise, one with a saddle-shaped shell.

My goodness, I'm glad I got that out correctly.

You can see just on the ground there's not, it's just dirt.

There's not very much vegetation on the ground.

So it is constantly having to reach its neck up to try and reach food from higher up.

Islands that have more humid climates have more vegetation on the ground.

Again, you can see if you look at the dome-shaped tortoise, so the, the bottom tortoise, like the ground is green.

There's tonnes and tonnes of plants on there.

So these tortoises with dome-shaped shells.

They don't need to reach up for food from higher up.

They eat plants that grow low on the ground.

Let's check to see if you're following that so far.

Which of the following is why some Galapagos tortoises have saddle-shaped shells? I did it.

Okay.

Right.

Is it A, some tortoises stretch up to get food and they pass this onto their offspring.

B, the shape of tortoise's shells has no relationship to the food they eat or see tortoises or saddle-shaped shells, oh my goodness.

We're more likely to survive as they could reach food.

Right.

Okay.

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

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

Okay.

The answer is C, tortoises with saddle-shaped shells.

I did not realise what a tongue twister that would be when I wrote this lesson.

I'm really regretting use using this as an example now.

Oh, okay.

So they were more likely to survive as they could reach more food.

Well done if you got that right.

So let's talk about how these different shell shapes evolved.

The differences in shell shape are result of speciation.

Darwin suspected that Galapagos tortoises descended from one species from mainland South America.

And modern DNA confirms this.

This might sound confusing as I did just tell you that the Galapagos Islands were 500 miles from South America and tortoises don't swim.

They're not turtles, they're not very good at swimming.

So this can be difficult to kind of visualise, but this is something that happens in nature not all the time, but it is something that is observable.

For example, in the 90's there was an example, there was a hurricane in the Caribbean and it moved green iguanas to islands that had, there had never been green iguanas on before.

And so this was, this was in the 1990's, you know, people had cameras.

This was, this was observable, documentable.

This isn't like thousands of years ago, or there might seem like ages ago to you.

But yeah, they noticed that green iguanas were located in one location before the hurricane.

After the hurricane, there were green iguanas distributed on islands that there had never been green iguanas before.

So this can happen.

And sometimes it doesn't have to be as crazy as a hurricane.

It can be animals that are kind of hitchhiking on rafts or like on logs or trees that have been blown over in storms and making their way from one island to another.

So it is a rare occurrence.

It doesn't happen every single day, but it is something that is observable.

So it is still around 3 million years ago, a small group of tortoises, maybe one pregnant female or a small as just like a breeding, a breeding pair of tortoises were carried across the ocean from mainland South America to the Galapagos Islands.

And those on different islands were geographically separated from each other by the sea.

So the tortoises came from mainland South America to the Galapagos Islands, and then they were geographically separated.

So again, whilst it is possible for land-based animals to travel across sea, like an example they just gave, floating on trees leftover from storms, it doesn't really happen that regularly.

So even though it is technically possible, we can still consider these populations of tortoises on different islands to be reproductively isolated.

This means that they were not able to mate with each other due to their geographic separation, that is being on different islands.

So conditions on each island were different.

So different adaptations were useful on different islands.

On islands with little food on the ground, saddle-shaped shells became more common as tortoises that could reach their necks up high to reach food were more likely to survive and reproduce.

So again, that's like the example at the top.

saddleback, the saddlebacked tortoises.

You can see the environment it's in not very much food on the ground.

It's got that clearance between the bottom of its neck and the top of its shell so that it can reach up.

That adaptation was super useful in that environment.

And so that's why that evolved.

When islands with plenty of food on the ground, dome-shaped shells became more common as tortoises did not need to reach their next up to reach food.

And these shells provide more protection for their neck and their head.

So over generations, natural selection occurred whilst the populations of tortoises on different islands were isolated.

This happened for such a long time and the tortoise became so different that saddleback and domed tortoises could no longer make with each other to produce fertile offspring.

They've become different species.

Let's see if you understood that.

Put these statements in order to describe the process of speciation.

A, Two populations of the same species became geographically separated.

B, natural selection occurs the different conditions in the different areas cause different traits to become more common.

C, eventually the populations are so different from each other, they can no longer inter-breed and are a different species.

D, the populations are unable to mate with each other, so are reproductively isolated.

Take five seconds or if you want more time, click pause.

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

Okay, let's look at the answers.

So first we have A, two populations of the same species become geographically separated.

D, the populations are unable to mate with each other.

So are reproductively isolated.

B, natural selection occurs.

The different conditions in the different areas cause different traits to become more common.

And finally, C.

Eventually the populations are so different from each other, they can no longer inter-breed and are different species.

Great job if you got that right.

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

The Galapagos tortoises descended from one species from mainland South America.

Explain how reproductive isolation and natural selection caused different species of tortoise with different shell shapes to evolve.

So you'll need to pause the video now to give yourself enough time to think about the answer.

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

Let's have a look at the answer.

So populations of the same species of tortoise became geographically separated on the different Galapagos islands.

They could not reach each other to mate, so they were reproductively isolated.

Natural selection occurred within the different populations of tortoise, but because of the conditions of the islands were different, different traits had an advantage.

In islands with dry climates, saddleback shaped shells have had the advantage as the tortoises could more easily reach food from higher up.

As saddle-shaped shells were an adaptation on dry islands, these tortoises were more likely to survive, reproduce, and pass on their traits to their offspring.

And for generations, saddle-shaped shells became more common on dryer islands, on islands with more humid climates, dome-shaped shells had the advantage as the shells provided more protection for the neck and head of the tortoises.

Tortoises with dome-shaped shells were more likely to survive, reproduce, and pass on their traits to the offspring on humid islands.

Over generations, dome-shaped shells became more common on humid islands.

If I never have to say the word shell again, I'll be very, very happy.

Oh my goodness.

Right.

Okay, well done if you got that right.

Right, we are done for today's lesson.

Let's recap what we've learned to help us remember it.

Scientists think all modern species of all from a common ancestor.

Natural selection is a process that causes each generation of species to become better adapted to its environment.

Natural selection can lead to speciation, which is the forming of new species.

Geographic barriers can lead to populations of the same species becoming reproductively isolated.

This reproductive isolation, natural selection can lead to speciation.

The Galapagos us is an example of a species that has undergone speciation due to geographic isolation.

Again, really, really great job.

I hope you enjoyed the lesson, and I hope to see you soon again for our next lesson.