Classification

All organisms can be grouped into different categories - called taxa - which allows us to determine similarities and differences between different organisms. Organisms which occupy the same taxonomic groups will have a more recent common ancestor than those who share fewer groups. All organisms are given a binomial (two part) Latin name which is adopted by scientists all over the world to avoid confusion when referring to living organisms.

Taxonomy

To make it easier for scientists to identify and study living organisms, each organism is organised into different groups based on their similarities and differences. The grouping of organisms according to their characteristics is called taxonomy. There are eight different taxonomic groups used to classify organisms. The groups are organised in a hierarchy from largest to smallest. The first group, domain, is the most broad category whereas the last group, species, is the most specific category. These groups do not overlap with one another, so an organism which is placed in the kingdom ‘animals’ will not share the same categories as an organism which belongs to the plant kingdom.

It’s useful to use a mnemonic to help you remember the order of the taxonomic groups. The classic one is ‘Dear King Phillip Came Over For Good Soup’ but my favourite is ‘Delicious King Prawn Curry Over Fatty Greasy Sausages’.

Binomial system

In the past, organisms were referred to by local and colloquial names and there were often hundreds of different names used to refer to the same organism. To make things more straightforward, scientists now use the binomial system for naming organisms. This two name system uses first the genus name and then the species name to refer to each organism. The scientific name for human beings is Homo Sapiens since ‘homo’ is the genus name and ‘sapiens’ is the name of our species. Likewise, the scientific name for the chimpanzee is Pan Troglodytes, which makes ‘pan’ the name of the genus and ‘troglodytes’ the name of the species.

Molecular Phylogeny

Scientists often use data from molecular phylogeny studies to decide which organisms to place into which categories. Molecular phylogeny is the study of molecules (such as DNA, RNA or amino acids) within an organism. Scientists will first choose a gene which is present in the two organisms that they want to compare and then line up the DNA base sequence or amino acid sequence. By looking at how similar these sequences are, the scientists can determine how closely related the two organisms are. The more differences in the nucleic acid or amino acid sequence, the more distantly related the two organisms and the further back in time they shared a common ancestor.

Scientists are continually discovering new species that we never knew existed. Once molecular phylogeny studies on the organism have been carried out, the data will be shared and evaluated by other scientists in scientific journals, conferences and peer review. Other scientists will repeat the experiment to confirm that they also get the same results. If the scientific community agrees with the findings, then the organism will be officially classified into particular taxonomic groups.

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