Charles Darwin and the Theory of Evolution

Charles Darwin and the Theory of Evolution

Charles Darwin

• Darwin was a British naturalist- someone who studies nature.

• He joined an expedition to South America in 1831 to study new species of plants and animals on board a ship called the HMS Beagle.

• The expedition sailed along the South American coast and ended in the Galapagos Islands.

• Along the way Darwin made some observations on the things he had seen.

Darwin's Observations

• On his journey Darwin studied a fossil of an extinct species of giant sloth. Where did it go? Why did it die out if there are still sloths alive today?

• On the Galapagos he noticed that on each seperate island there were different species of finches that were similar but had slight variation in the shape of their beaks, their size, colour and diet. Why were they all different?

• He also studied the species of tortoise found there. Some were small with short necks, and some where giant with long necks. Why??

The Common Ancestor

• Darwin began to theorise that these species shared a common ancestor and through a process called natural selection, adapted to the environment they were in.

• A common ancestor of the finches and tortoises must have been trapped on the Islands when sea levels rose and then adapted to the environment they were in.

• These adaptations made them different, even though they all came from a common ancestor.

Natural Selection

• This adaptation Darwin called natural selection.

• Let's use the finches as an example. A species of blue finch that eats fruit inhabits a jungle. There's lots of food and the blue helps it find mates. The jungle is huge, it can easily escape predators.

• But then the sea rises, and the jungle becomes a bunch of islands. Some birds are stuck on big islands, some on small islands. On some islands there's lots of food, on some there is little food. On some there's lots of fruit, others nuts, on the next insects.

• Let's imagine the situtaion where a blue finch get trapped on a small island with little fruit. Now it's harder to escape predators because the island is small

• The blue makes the finch easy to spot, and they eat fruit, not bugs.

• A pair of finches has some chicks, let's say 4. Two of them are blue, like mum and dad, but there are mutations in their genes so one is brown, and the other one is black with a larger beak.

• In a normal environment with lots of fruit and no predators the two blue would survive and the brown and black would die. How would they find mates if they aren't blue? How would the black one eat fruit with a funny beak?

• But the environment has changed.

• The brown bird can hide in the brown grass from predators and finds it can peck the ground for insects to eat.

• The black bird can hide under the trees shadow and avoid predators, it's large beak means it can catch bugs flying in the air.

• The two blue birds are caught by predators and die.

• Elsewhere in the jungle another pair of blue birds also has chicks that come brown and black.

• The brown and black birds find each other, breed and have brown and black chicks. Sometimes thanks to their genes from their parents they have blue chicks, but these are easily caught by predators. There are no more blue finched surviving to breed.

• As a result now on the island where there was one species of blue fruit eating finch there are now two species of insect eating finch, each occupying different niches in the environment- the brown finch becomes a ground dwelling crawling insect eater, the black finch becomes a tree dwelling flying insect eater.

• Both are different species and cannot breed with each other, but both share a common ancestor.

• These changes happen over many years. The best genes survive to breed, genes unsuited to the environment die out and don't pass on their genes.

• This is natural selection.

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"On the Origin of Species"

• Darwin put all his findings into a book entitled "On the Origin of Species".

• It caused waves in the scientific world and still remians one of the most important scientific books ever published.

• It also shook peoples understanding of how the world was made and where we came from.

• Darwin argued that all species were descended from a common ancestor adn over time, thanks to changes in the environment, had adapted and evolved to become the species they are today.

A Bit Confused?

This is a very scientific topic and delves into a lot of things that we may not all understand- genes, DNA, mutations etc.

Watch the video on the next slide and see if that helps!