How does natural selection work?

Note: Keywords which are vital for marks will be highlighted in bold.

 

Within all populations, there is variation.

This is due to different alleles (types) of different genes being present in different individuals. (We are all different heights - this is an exapmple of variation).

 

Random mutations of genes are constantly occuring within individuals. These mutations form different alleles. 

 

These mutations may change something in the body. This could be disadvantageous, make no difference, or be advantageous.

 

Individuals with these advantageous alleles will survive longer than others without this advantage.

Therefore they will reproduce more, and pass on this allele more.

 

Over many generations, this will lead to an increase in frequency of these alleles - more and more people will have this allele.

 

The allele is therefore selected for. This is Natural Selection.