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Technology associated with biology has advanced throughout the years, which has allowed the current classification system to be enhanced by using microscopes, biochemistry and DNA evidence.

Originally Linnaeus's 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.

The development and study of biochemistry and the processes undertaken inside the cells, in some cases, have allowed any ambiguities within this classification system to be clarified.

The comparisons of DNA sequences have allowed the relationship of organisms to be explored further. In some cases, species that are more closely related may have fewer differences contained within the DNA sequences.

Three-domain system

Classification systems have continued to be developed by other scientists, such as Carl Woese who developed the three-domain system. This is based on evidence now available from chemical analysis.

The updated system divides organisms into:

• Archaea (primitive bacteria usually living in extreme environments)
• Bacteria (true bacteria)
• Eukaryota (including protists, fungi, plants and animals)

Evolutionary trees

Evolutionary trees are a method used by scientists to represent the relationships between a set of organisms. The tips of the tree often represent different species and where two branches join, this represents a common ancestor for those two species. They can be created from current data such as DNA analysis and existing fossil data.

Evolutionary trees can be created using DNA sequences of different species. This allows scientists to examine the differences at a DNA level, which may have led to evolutionary splits millions of years ago.