Species & Taxonomy (AQA A-Level Biology): Revision Notes
Species
What is a species?
A species represents the foundational unit used in biological classification systems. Defining exactly what constitutes a species can be challenging, but scientists have established one key characteristic that unites all members of the same species.
Members of the same species can interbreed to produce living, fertile offspring. This reproductive compatibility means that when sexual reproduction occurs between individuals of the same species, their genetic material can combine successfully to create descendants that are themselves capable of reproduction.
The ability to produce fertile offspring is key - while some different species can mate (like horses and donkeys), their offspring (mules) are typically sterile, meaning they cannot reproduce. This sterility indicates that horses and donkeys are separate species despite their ability to mate.
This breeding criterion is essential because it ensures genetic continuity within the species. When individuals reproduce sexually, genes from both parents can theoretically combine with those of any other member of their species, maintaining genetic diversity within the population.
The binomial naming system
Historical development
Before standardised naming systems existed, organisms often received descriptive names based on their appearance, such as "blackbird" or "rainbow trout". This approach created significant problems because the same common names were used for completely different species across different regions, leading to scientific confusion.
Carl Linnaeus and Scientific Revolution
The Swedish botanist Linnaeus solved this problem over 200 years ago by developing a universal naming system that scientists still use today. His work, published in "Systema Naturae" (1735), revolutionised biological classification and established the foundation for modern taxonomy.
This system ensures that every species has a unique, internationally recognised scientific name.
How binomial nomenclature works
The binomial system assigns each organism exactly two names, creating a unique identifier for every species:
- Generic name: This first name indicates the genus to which the organism belongs. Think of this as equivalent to a family surname - it groups together closely related species that share similar characteristics and evolutionary history.
- Specific name: This second name identifies the exact species within that genus. Unlike human naming systems, each specific name is unique within its genus, ensuring no confusion between different species.
Rules for scientific naming
Essential Rules for Scientific Naming
- Names derive from Latin or Greek terminology to ensure universal understanding
- The generic name always begins with a capital letter, while the specific name uses lowercase letters throughout
- Scientific names appear in italics when printed, or are underlined when handwritten to distinguish them from common text
- When the exact species is unknown, scientists can write the generic name followed by "sp." (for example, Felis sp.)
Dynamic nature of naming
Scientific names change as our understanding of organisms develops. New discoveries about evolutionary relationships, physical characteristics, biochemical properties, and behavioural patterns can lead to reclassification of species, reflecting the ongoing advancement of biological knowledge.
Key Points to Remember:
- Species are defined by their ability to interbreed and produce fertile offspring - this is the key characteristic that unites all members of a species
- The binomial system gives each species two names: a generic name (genus) and specific name (species), creating a unique scientific identifier
- Scientific names follow specific rules: generic names are capitalised, specific names are lowercase, and both appear in italics when printed
- Courtship behaviour evolved to help individuals recognise their own species and assess mate suitability, ensuring successful reproduction
- Courtship serves multiple functions including species recognition, mate assessment, pair bonding, and reproductive timing coordination