Explain the Theory of Natural Selection

There are four key points to natural selection:

• first, that individuals in all species show variation
• second, that this variation is genetic and therefore heritable
• third, that certain characteristics give the individuals which have them a greater chance of survival and reproduction in the environment they are in
• and finally that this results in the genes coding for favourable traits being passed on to the next generation

So genes which code for traits which aid survival and/or reproduction have a higher chance of being passed on to offspring, meaning that these traits are expressed in a higher proportion of individuals in the next generation, and eventually end up being expressed in the majority of individuals.