Natural Selection

Evolution occurs via natural selection:
− individual organisms within a particular species may show a wide range of variation because of differences in their genes
− individuals with characteristics most suited to the environment are more likely to survive to breed successfully
− the genes which have enabled these individuals to survive are then passed on to the next generation.
Where new forms of a gene result from mutation there may be more rapid change in a species.

Variation occurs naturally. Each of the flowers below is genetically unique just as all humans on Earth, apart from identical twins, are unique.

Each flower is in competition with all the other for the resources it needs to live. Space, water, nutrients and sunlight. If certain individuals have an advantage over others then they will be more likely to survive and so more likely to reproduce. Their genes will be more likely to be passed on to the next generation of flowers.

For example;
Some flowers may have longer roots than others. This may give them an advantage in absorbing water and nutrients from the soil.
Some flowers may have brighter petals than others. These will have a better chance of attracting the insects needed for pollination.
Some flowers may be slightly taller. These may have an advantage in getting the sunlight needed for photosynthesis.

From generation to generation small changes will occur but over millions of years the species may change quite significantly, becoming better and better suited to its environment. This process is called natural selection.

Life in the wild is not easy. Small differences can make the difference between being able to get enough food to live or not being lunch for a predator. Only the individuals which are best suited to their environments survive.

Sometimes a significant change occurs due to a mutation. This is a genetic change caused by a mistake when genes reproduce. Most mutations are useless and the individual does not survive but sometimes it can produce a significant advantage and evolution can take a big step very quickly.

During the industrial revolution soot covered the trees of the forests near centres of industry. A mutation occurred in the white peppered moth which made it black. This happened to be excellent camouflage and these moths were much less likely to be eaten by birds. Black moths grew rapidly in numbers while white speckled moths dwindled in numbers.