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The many different species of living things on
Earth (and many species that are now extinct) evolved from very simple
living things.
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Life on Earth began about 3500 million years ago.
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Evidence for evolution is provided by fossils and
from analysis of similarities and differences in DNA of organisms.
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The first living things developed from molecules
that could copy themselves.
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These molecules were produced by the conditions
on Earth at that time, or may have come from elsewhere.
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Evolution happens due to natural selection.
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The process of natural selection involves variation,
competition, increased chance of survival and reproduction, and increased
number of individuals with certain characteristics in later generations.
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Both environment and genes cause variation, but
only genetic variation can be passed on.
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The difference between natural selection and selective
breeding is that people have carried out selective breeding with the
aim of improving a species.
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Changes can occur in genes, they are called mutations.
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Mutated genes in sex cells can be passed on to
offspring and may occasionally produce new characteristics.
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The combined effect of mutations, environmental
changes and natural selection can produce new species.
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If the conditions on Earth had, at any stage, been
different, evolution by natural selection could have produced different
results.