Classification

What is classification and why is it important?

Classification is the process of organising living organisms into groups based on their shared characteristics and evolutionary relationships. It is important because it allows scientists to identify and name organisms consistently across different languages and countries, to study and compare organisms more easily, to predict shared characteristics between related organisms, and to understand evolutionary relationships between species.

What is the taxonomic hierarchy and what are the levels in order from largest to smallest?

Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species. Each level is called a taxon (plural taxa). As you move down the hierarchy, the groups contain fewer organisms that share more characteristics with each other.

What is the binomial naming system and what are its rules?

The binomial system gives every species a unique two-part Latin name consisting of the genus name (first, capitalised) and the species name (second, lower case). For example, Homo sapiens for humans. The name is written in italics when typed or underlined when handwritten. The advantages of this system are that it is universally understood by scientists regardless of language, it is unique to each species avoiding confusion with common names, and it reflects evolutionary relationships (organisms sharing a genus name are closely related).

What is the biological definition of a species?

Under the biological species concept, a species is a group of organisms that can interbreed to produce fertile offspring and share a common gene pool.

Why is the biological species concept difficult to apply, and what is an alternative concept?

It cannot be applied to asexually reproducing organisms (e.g. bacteria) or extinct organisms known only from fossils, and it breaks down in cases of hybridisation (e.g. ligers).