Understanding Zoological Nomenclature: Valid vs. Invalid Scientific Names
In the scientific community, precision is essential for communication. When researchers discuss animals, they rely on a standardized system known as zoological nomenclature. This system ensures that every taxon—a specific group of organisms, such as a species or genus—has a unique and universally recognized name. However, determining which name is the "correct" one can be a complex process governed by strict rules.
A valid name is the correct scientific name for a taxon, given a specific circumscription (the defined boundaries or description of that group). To be considered valid, a name must first be an available name under the rules set by the International Code of Zoological Nomenclature (ICZN). If a name is not "available" according to these rules, it cannot be classified as either valid or invalid.
The Concept of Invalid Names
An invalid name is a name that is considered "available" under the ICZN rules but is not the correct name for a particular taxon. Invalid names are categorized into two distinct groups: those based on scientific opinion and those based on indisputable facts.
Subjectively Invalid Names
Subjectively invalid names are those rendered invalid by individual scientific judgment or opinion. Because taxonomy often involves interpretation, what one researcher considers invalid, another may consider valid. These include:
- Junior subjective synonyms: These occur when different types are described as separate taxa, but researchers later believe they actually belong to the same taxon. The "junior" (later) name is only treated as invalid as long as the scientific opinion holds that the two names refer to the same group.
- Junior secondary homonyms: This happens when two different species, originally described in different genera, are later placed into the same genus and end up sharing the same name. Generally, only the "senior" (older) name remains valid. If a name became a secondary homonym before 1961 and was replaced, the original name may be permanently invalid.
- Conditionally suppressed names: These are special cases where the ICZN rules that a name is only valid under specific conditions. This often occurs when a junior synonym has achieved much wider and longer common usage than the older, senior synonym.
Objectively Invalid Names
Unlike subjective names, objectively invalid names are rendered invalid for indisputable reasons. These names are universally accepted as invalid and do not depend on individual scientific opinion. They include:
- Junior objective synonyms: These are synonyms described from the exact same types. In these cases, the ICZN follows the Principle of Priority, which dictates that the oldest available name for a taxon is generally the valid one.
- Junior homonyms in the family and genus group: These are names of families or genera that have identical spellings but refer to different taxa. Only one can be valid; junior family-rank names must usually change their spelling or be replaced, while junior genus-rank homonyms must be replaced.
- Junior primary homonyms in the species group: This occurs when two different organisms are originally described with identical names within the same genus. Typically, only the senior homonym is valid, though they may both be valid if they are later moved to different genera.
- Completely suppressed names: These are names that the ICZN has ruled are completely suppressed. They are treated as if they had never been published and are never to be used.
- Partially suppressed names: These names are acknowledged as having been published but are used only for the purpose of homonymy (identifying identical names) rather than for establishing priority.
Comparison of Invalid Name Categories
| Feature | Subjectively Invalid Names | Objectively Invalid Names |
|---|---|---|
| Basis of Invalidity | Scientific judgment or opinion | Indisputable facts |
| Consistency | May vary between researchers | Universally accepted |
| Key Example | Junior subjective synonyms | Junior objective synonyms |
Differences in Botanical Nomenclature
It is important to note that the rules for naming plants, algae, and fungi differ from those in zoology. Under the International Code of Nomenclature for algae, fungi, and plants, the terminology changes:
- The botanical equivalent of a zoological "available name" is a validly published name.
- The botanical equivalent of a zoological "valid name" is a correct name.
Key Facts
- A name must be available under the ICZN to be considered either valid or invalid.
- Subjective invalidity is based on the varying opinions of taxonomists.
- Objective invalidity is based on undeniable scientific facts.
- The Principle of Priority ensures the oldest available name is usually the valid one.
- Suppressed names are special cases managed by the ICZN to maintain nomenclatural stability.
Frequently Asked Questions
What is the difference between a valid name and an available name?
An available name is one that has been published according to the formal rules of the ICZN. A valid name is an available name that is also the correct name for a specific taxon.
What is the Principle of Priority?
The Principle of Priority is a fundamental rule in zoological nomenclature stating that the oldest available name applied to a taxon is generally the one that must be used as the valid name.
Why are some names considered "subjectively" invalid?
Subjective invalidity occurs when scientists disagree on whether two different descriptions actually belong to the same organism. Because this is a matter of scientific interpretation, the status of the name can change depending on the researcher's opinion.
What is a homonym in taxonomy?
A homonym occurs when two different taxa are given the same name. To maintain clarity, the rules of nomenclature generally require that only one of these names (usually the older one) remains valid.
How does botanical naming differ from zoological naming?
While the concepts are similar, botany uses different terms. In botany, the term "correct name" is used instead of "valid name," and "validly published name" is used instead of "available name."