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