What is natural selection?

A mutation of the gene leads to a change in the phenotype of the organism. For natural selection to occur this change must give the organism an advantage and therefore it has a higher chance of survival. If it has a higher chance of survival, then it is more likely to reach the age at which it will reproduce. It will pass down this mutated gene to its offspring and pass on the advantage. The proportion of the population with this mutated gene will increase due to the higher survival rate until eventually all of the population possesses it. This happens over several generations. For example, if a giraffe has a genetic mutation which gives it a longer neck it allows it to reach leaves higher in the trees than other giraffes and therefore it will have more food and a greater survival chance. This giraffes offspring will inherit the gene for this characteristic and also have the same benefits.