Transcript Planet Earth

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
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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