Classification refers to the categorical organisation of living organisms to help clarify the relationships between them.
Carl Linnaeus in the 1700's proposed the Linnaean system, which focuses on dividing beings using their unique characteristics.
It's a 7 category system that starts with kingdoms- like the animal kingdom or the plant kingdom!
From here, the categories are:
Phylum, Class, Order, Family, Genus, and finally Species.
Here are a few ways to remember the ordering of the Linnaean system:
But for naming organisms, biologists use the binomial system, meaning each living thing gets two Latin names, starting with the organism’s genus (to tell us its heritage) and ending with the species!
Let’s take an example: have you heard of Homo Sapiens? Well, that’s actually us- we're in the 'Homo' genus and part of the 'Sapien' species!
However, as time has passed, new biological theories and technological advancements like the microscope have furthered classification greatly.
This invention especially highlighted the internal biological processes within living things, which scientists have used to improve their classification models.
In the 1990's, Carl Woese used data from chemical analysis to make the ‘three-domain system’ of classification. He separated living things into 3 domains:
Thought to be primitive bacteria, we now know these are a type of prokaryotic cell like bacteria, and are considered to live in extreme areas like hot springs.
These are true bacteria, but have key characteristics different from Archaea.
Protists, fungi, plants and animals.
Finally, sorting organisms based on characteristics helps us understand their similarities and differences, like using evolutionary trees.
These are diagrams that help to visually display how closely related different beings are to each other.
This can be done for living life forms using up-to-date classification data but we can also look back and organise extinct beings through what we know from their fossil remains.