Species—Definition and Nomenclature | Geology Optional for UPSC PDF Download

Introduction

• Taxonomic Classification: Taxonomic classification refers to the system of categorizing and naming organisms based on shared characteristics. This system was first proposed by Linnaeus, and it involves organizing organisms into a hierarchy of categories, starting from the broadest category, kingdom, and moving to more specific categories.
• Hierarchy of Categories: The hierarchy of categories includes seven obligate categories, which are the essential levels of classification. These categories are arranged in a descending order, with each level becoming more specific. In addition to the seven obligate categories, certain intermediate categories have been added to make the taxonomic position of species more precise.
• Species Concept and Taxonomic Limitation: When studying a particular taxon, a taxonomist must adopt a species concept and provide a limitation to define the taxon. This is important because defining and recognizing a species can be controversial, and different concepts may lead to different conclusions about the variation and limitation between species.

What is a Species?

• The term 'Species' comes from a Latin word that means 'appearance' or 'kind'.
• Linnaeus, an early scientist, described species based on their morphology, which is the study of the form and structure of organisms.
• However, modern taxonomists have expanded this concept by considering genetic and behavioral differences when defining species.
• A species is now understood to be a natural population of individuals or a group of populations that can interbreed freely and produce fertile offspring.
• Members of the same species resemble each other in all essential morphological and reproductive characteristics.

Different Concepts of Species

A species is both the unit of evolution and the unit of classification. Only a species undergoes the processes of reproduction and modification. There are various concepts regarding the definition of a species, which can be categorized into historical and modern concepts.

Historical Concepts:

• Static Concept: Proposed by Linnaeus, this concept views species as unchangeable. According to Linnaeus, the characteristics of species do not change over time; the species present today are the same as those in the past and will remain the same in the future. He believed in the theory of special creation, which posits that all living organisms were created by God, who provided them with a basic size and shape that has not changed.
• Typological Concept: This concept focuses on the idea that species are defined by a set of fixed characteristics or a typical example.
• Nominalistic Concept: According to this concept, species are considered to be mere names or labels for groups of individuals that share similar characteristics.
• Dynamic Concept: This concept acknowledges that species can change and evolve over time.

Modern Concepts:

• Evolutionary Concept: This concept views species as groups of organisms that share a common ancestry and are capable of evolving over time.
• Biological Concept: According to this concept, species are groups of individuals that can interbreed and produce fertile offspring.

Dynamic Concept of Species

The dynamic concept of species was proposed by Lamarck as a counter to the static concept. According to Lamarck, species are not fixed but are always changeable. He believed that changes occur in the characteristics of species from one generation to another, and this process is known as evolution.

Typological Concept of Species

The typological concept of species was proposed by ancient philosophers Aristotle and Plato. According to this concept, there is a specific type or pattern of characteristics that define each species of living organisms, and all members of a species closely resemble this pattern.

This concept includes:

1. Monotypic Species: Species that have a single, uniform pattern or resemblance among all their members.
2. Polytypic Species: Species that exhibit more than one type or pattern of characteristics within their members.

Nominalistic Concept

The nominalistic concept, as proposed by Buffon and Robinet in 18th century France, argues against the existence of "real" universals in nature. According to this view, only individual organisms exist, and species are mere abstractions created by humans.

Buffon and Robinet believed that "Nature produces individuals and nothing more. Species have no actual existence in nature." This perspective contrasts with the evolutionary concept of species, which acknowledges the reality of species in the natural world.

Evolutionary Concept

An evolutionary species refers to a group of organisms that share a common ancestor. Over time, as evolution occurs, members of this group may diverge from one another. When this divergence becomes sufficiently clear, the populations are recognized as separate species.

Phenetic Species Concept: This concept focuses on phenetic similarity as the primary criterion for recognizing separate species. Phenetic characters encompass all observable or measurable traits, including behavioral, anatomical, and morphological characteristics.

Mayer's Concept of Species

Mayer defines a species as a group of individuals that can interbreed with one another and produce fertile offspring.

Biological vs. Taxonomic Species

• Biological Species: This concept is based on the ability of organisms to interbreed. For example, all humans belong to the same biological species because they can interbreed and produce fertile offspring.
• Taxonomic Species: This concept is based on other characteristics, such as morphology (physical appearance). For instance, two organisms might have similar physical traits and be classified as the same taxonomic species, even if they cannot interbreed.

Example: Euglena sanguinea and Euglena laciniata

These two organisms have similar morphological characteristics and belong to the same taxonomic species. However, they are different biological species because they cannot interbreed.

Limitations of Mayer's Concept

• Asexual Reproduction: The concept is incomplete because it only applies to sexually reproducing organisms. Many organisms reproduce asexually, and this definition does not account for them.
• Interbreeding: While interbreeding is a key factor in determining species, it is not always used in taxonomy.

Few Terms Related to Species

Ecotypes. Members of the same species living in different environments and having some genetic variations are called ecotypes. These members can interbreed among themselves, but due to geographical barriers, they cannot interbreed with others.

For example, crows ( Corvus splendense. found in different regions are ecotypes of one species:

• Corvus splendense splendense. Indian crow
• Corvus splendense insolence. Myanmar crow
• Corvus splendense protegatus. Sri Lankan crow

Ecads. Members of the same species with genetic variations due to environmental factors are called ecads.

Sibling Species. Sibling species are members of a species that are morphologically similar but reproductively isolated from each other.

Conclusion

There isn't a single definition of "species" that all naturalists agree on, yet every naturalist has a general idea of what they mean when they use the term. From a biological standpoint, a species can be defined as a group of organisms within a population that can interbreed freely and produce fertile offspring. While this concept is still valid today, it is considered incomplete.

Nomenclature of Fossils

The nomenclature of fossils refers to the system of naming and classifying fossilized remains of organisms. This system is crucial for organizing and identifying the vast diversity of species that once inhabited our planet. Here are some key points about the nomenclature of fossils:

• Linnaean Nomenclature: The system of nomenclature for species, widely adopted today, was developed by the Swedish naturalist Carl Gustav Linnaeus. It involves giving every species a double name, consisting of a generic name and a specific name. This system is known as binomial nomenclature.
• Example: For instance, the scientific name Stegodon ganesha refers to a specific species of elephant. "Stegodon" is the generic name, indicating the genus to which the species belongs, while "ganesha" distinguishes this particular species.
• Description of New Species: When describing new species, paleontologists often assign them to existing genera, requiring the invention of only one name. If a new species is distinct from all established genera, a new generic name is created simultaneously.
• Language of Names: The names for species and genera must be Latin words or Latinized forms. There is flexibility in choosing words for names, which can include Latinized place names, names of scientists, mythological characters, or descriptive compound words of Latin or Greek origin.
• Sub-generic Names: Paleontologists may introduce sub-generic names to provide additional details about the denomination. The sub-generic name is written in parentheses between the binomen (generic and specific name).
• Suffixes for Generic Names: As the number of generic names increases, there is a tendency to develop similar generic names for related classes. For example, crinoids often end with "crinus," corals with "phyllum" or "phyllia," and echinoids with "aster."
• Specific Names: The specific name may describe a feature of the species, indicate its first locality, or be a noun. Popular names may be rejected in favor of new names, with earlier names indicated in brackets.
• Higher Categories: Categories higher than genus are designated in Latin, using conventional suffixes such as "inae" for sub-family, "idae" for family, "acae" for super family, "ina" for sub-order, "ida" for order, and "oidae" for class.
• Fossil Plants: Fossil plants are named according to the same rules, but the names usually refer to parts rather than complete organisms. The generic name may apply to only a seed, leaf, or other parts, leading to the use of form genera or artificial genera. For example, the arborescent lycopod Lepidodendron represents the whole plant, while its roots, leaves, cones, and spores have separate names like Stigmaria, Lepidophyllum, Lepidostrobus, and Triletes.

Note: The generic name Stigmaria is also applied to similar roots of different plants such as Lepidophlois, Bothrodendron, and Sigillaria.

Rules for Writing Organism Names

When writing or printing the names of organisms, certain rules must be followed to ensure clarity and consistency. These rules apply to both generic names and specific names.

• Generic Names: Generic names should always be written with an initial capital letter. This helps distinguish the genus to which the organism belongs.
• Specific Names: Specific names should be underlined to indicate their significance. This differentiation is important as it specifies the particular species within the genus.
• Printing in Italics: When printing organism names, they should be printed in italics. This includes adhering to the rule of using an initial capital letter for the generic name and an initial small letter for the specific name. For example, "Panthera leo" (Lion) follows this format.