Technological advances in biological equipment have allowed the current classification system to be developed. Three key advances have helped this development:
Originally Linnaeus’ system relied purely on human judgement in order to compare the characteristics of various organisms. The development of microscopes allowed cells to be examined in far more detail. Organelles within the individual cells could be distinguished and this allowed a more scientific approach of classification based on observations. Classification that is based purely on observations is referred to as artificial classification.
Phylogenetics is the study of how related organisms are. It helps us to work out how species have evolved from one another. Molecular phylogenetics focuses on comparing the molecules inside of organisms to see how similar they are. The more similar the molecules, the more closely related the species. This is referred to as natural classification.
Developments in biochemistry mean scientists can work out how similar organisms are on a molecular level, rather than just using characteristics that can be seen with our eyes or a microscope. For example, we can compare the structure of the proteins used in aerobic respiration between organisms to see how similar they are.
Comparing the DNA sequences of different organisms has allowed the relationships of organisms to one another to be explored even further. Species that are more closely related are likely to have fewer differences in the sequence of their DNA bases.
In the diagram, species A and B have very similar sequences of DNA so they must be closely related. Species A and E, however, have more differences in their sequence of DNA and therefore they must be more distantly related to one another than A and B.
Classification systems have continued to be developed by other scientists. Carl Woese developed the three-domain system. This system is based on evidence now available from analysing organisms on the molecular level.
The updated system divides organisms into: