Planet Earth

Evolution – How it all began

Evolution

• Explains how species of living things have changed over time

• Supported by evidence from fossils, and by the rapid changes that occur in microorganisms such as antibiotic resistant bacteria

• Many species have become extinct, and this continues to happen.

Darwin

• English naturalist• Studied variation in plants

and animals during a 5 year voyage around the world in 19th century

• Darwin’s ideas caused a lot of controversy because they conflict with religious views about the creation of the world and the creatures in it

The Finches

• Galapagos Islands• Found that the finches were fundamentally similar• Showed variations in their size, beaks and claws from island to island• Eg. Beaks were different sizes depending on the local food source• Conclusion – Finches that arrived in the past must have changed

over time

Darwin’s Theory of Evolution

• Proposed after 30 years of research, in 1858• Says that all the different species have evolved

from simple life forms• These simple life forms first developed more than

3 billion years ago, bearing in mind that the earth is about 4.5 billion years old

Natural Selection

• Evolution happens by natural selection– Individuals in a species show a wide range of variation– The variation is because of differences in genes– Individuals with characteristics most suited to the

environment are more likely to survive and reproduce– The genes that allowed the individuals to be successful

are passed to the offspring in the next generation

• Individuals that are poorly adapted to their environment are less likely to survive and reproduce, which means that their genes are less likely to be passed to the next generation.

Evidence for Evolution

• Most evidence comes from the fossil record

• Fossils show how much or how little organisms have changed over time

• Fossil record does contain gaps

• Not all organisms fossilise well

• Many fossils have been destroyed by movement of the earth or not discovered

Fossils of ammonites - sea creatures that became extinct about 65 million years ago

The Horse

• One of the few animals that has a complete evolutionary record is the horse because all the main stages of the evolution of the horse have been preserved in fossil form. Over 60 million years, the horse evolved from a dog-sized creature that lived in rainforests into an animal adapted to living on the plains and standing up to 2 metres high.

Only a Theory

• This is one reason why the theory of evolution is still a theory, not a law. Since no-one was around millions of years ago to make observations, take notes and carry out experiments, evolution cannot be proved in the usual scientific sense. However, rapid changes in species have been observed that support the theory.

Extinction

• Individuals that are poorly adapted to their environment are less likely to survive and reproduce than those that are well adapted. Similarly, it is possible that a species that is poorly adapted to its environment will not survive and will become extinct.– changes to the environment, such as a change in

climate – new diseases – new predators – new competitors

There’s always two sides to an argument…

• What is the other side of this one? (What criticisms of the theory of evolution can you find?)

How did life begin?

• Discuss with reference to religious and scientific viewpoints