What a subtopic title indeed – organisms! I didn’t even make it up myself, it’s the spec. This topic is really about evolution. The basics of evolution, such as mutation, genetic drift, natural and sexual selection and allele frequency are covered in the Scottish Higher topics Evolution and Mutations, so this topic builds further on those concepts.

Previously we learned that evolution is the change in heritable traits through generations, brought about by random shifts such as genetic drift, as well as directed shifts such as selection.

In small populations, genetic drift is more powerful because the relatively small background fluctuations in allele frequency can actually result in some alleles being lost altogether rather than just slightly decreasing, as may be the case in a large population.

The variation present between organisms at the DNA sequence level is enabled through mutations of the code in genes, or the change in a…