Species Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Species is a definitional unit used by biologists and other life scientists to systematically classify the enormous numbers of life forms on the earth. The basic unit of classification is species, followed by larger groupings of related plants or animals. The term species was first used by the ancient Greeks. Taken from the Greek, the word ideos meant the shape or visible form of something-its form made it rationally comprehensible. Logically specifying the form of something as a specie of some species answered the question, “What is it?”

Millions of species have been identified and many more are discovered virtually every day. In general, a species includes all of the individual members of its natural population that are descended from common ancestors and that can breed indefinitely with each other. The interbreeding population share similar characteristics including appearance, genetics, and relatively recent ancestors. The factor of interbreeding is a very important defining characteristic. The interbreeding members of a species exchange hereditary material or genes with each other to produce offspring after their own kind, and a common gene pool is established within the species. Generally, differences between species prevent interbreeding through reproductive isolating mechanisms.

There are many species that are closely related to other similar species that do not normally interbreed. For example, wolves and dogs are closely related but do not normally interbreed, although in this particular case, they are capable of interbreeding. In some species, interbreeding produces hybrids, most of which are sterile and cannot breed. For example, horses and donkeys can and do interbreed, but the offspring are usually sterile mules produced by a male donkey and a female horse.

Classification

The term species is used in the scientific classification of plants and animals in order to provide a taxonomic system for organizing all plants and animals. The current system groups all individual plants and animals into a basic group called a “species.” The individuals in a species are assigned two names in Latin, which are often derived from Greek or Latin words.

The Latin naming system is called a binomial system because it uses two names as identifiers assigned to a new species. The first name is the genus name of the species and the second name is the special identifying name of the species. The binominal system of nomenclature enables scientists to name the plants and animals in exactly the same standard way regardless of individual variations. The binomial nomenclature enables individuals to be grouped into a useful category everywhere around the world. For example, dogs, found everywhere, are classified as the species Canis domesticus. The domesticus refers to its ancient taming by humans and close association with human domiciles. The naming of species is done by scientific bodies. They may use a name that is descriptive of a characteristic of the species or that recognizes the discoverer of a newly identified species. To aid in the work there are now international codes of ontological and botanical nomenclature.

However, many biologists and other life scientists who regularly engage in taxonomic work doubt whether one single scheme of classification will fit all life forms. Among biologists and other life scientists the so-called “species problem” is a controversial subject. There is considerable disagreement about how best to identify species, what constitutes a useful name, what is a genuine species, and how it is to be distinguished from similar but apparently different species that are not really different species but just differences in individuals. For example, black and blonde-colored cocker spaniels are not different species, but rather individuals with different characteristics. Such obvious differences are not always apparent among some of the more obscure forms of life.

Development of the System

Humans have been naming plants and animals from the beginning of human history. For example, Aristotle sought to develop a system for naming plants and animals. However, most names have been common names that are used locally and may change from one language to another. For example, the mountain lion, found throughout the Americas, is also called a cougar, puma, and panther. Its name varies in English, Spanish, Portuguese, and French. While its common name differs from language to language, its scientific name, Pelis concolor, is always the same.

Without a standard method for naming plants and animals, neither science nor related economic or cultural practices can advance. For example, there are many plants used in medicines. Ancient and medieval medical or pharmacological books will name these, but there is often uncertainty about which plant is really designated by the names used. The making of compounds for consumption as medicines or for other purposes from plants that may be different but similar species could result in harmful or ineffective products. The practical nature of efficient and economical human life has not only warranted the development of terminology for biological taxonomic use, but has compelled it.

A Swedish botanist and physician, Carolus Linnaeus, first developed the naming system, or taxonomy, for scientifically classifying plants and animals that is used today. He worked in the mid-1700s at a time when the voyages of the Age of Discovery were bringing a growing volume of information about plants and animals from around the world. Great numbers of these plants and animals, such as kangaroos and black swans, had been previously unknown to European scientists. In other cases, the plants or animal resembled those already known.

The need for a rigorous system of classifying plants and animals presented Linnaeus with a challenge he met in two ways. First, Linnaeus used the resemblances between closely related plants or animals to place them into specific species; the specific species were put in categories of classification after a close study of the specific traits of the species revealed its diagnostic characteristics. Second, Linnaeus began the work of organizing groups of similar species into broader categories. Today, the system most widely used divides all living things into kingdom (plants or animals), phylum, class, order, family, genus, and species.

Since the 1960s, some biologists have sought to expand the number of kingdoms by adding three more kingdoms. The three additional kingdoms in this proposed scheme are: the kingdom Monera, which includes all bacteria and other Prokaryotic cellular forms of life; the kingdom Protista, which includes algae and single-celled Eukaryotes; and the kingdom Fungi, which includes all fungi, yeasts, and molds that are currently classified as plants.

Advances in transportation since the beginning of the 20th century have allowed scientists to penetrate into ever more remote areas of the world. This has also included the development of technologies that have allowed exploration of the ocean depths. As a result, newly discovered plants and animals have poured into scientific centers, where the task of defining them as species has become almost overwhelming. There are several reasons for this problem.

The classification of species requires detailed study of the characteristics of individual specimens. The study has to not only record a description of the individual’s characteristics such as the color, number of feathers, type of feathers, beak characteristics, or other characteristics in a bird, but these characteristics then have to be compared with other similar species. There is no single standard way to do this kind of work.

Using observational characteristics does not automatically guarantee that the individuals in a new set of specimens being studied for classification as a new species will be seen as the same by all observers. The fact is that there are peculiarities in the individuals of a species. These individual characteristics may give rise to debates among biologists, ornithologists, or others depending upon the type of plant or animal in question. The debates could include issues about whether the characteristics are sufficient to create a different species, whether they make for subspecies, or whether the differences are unique at all.

Speciation

Speciation-the development of new species-proceeds with the breeding of members of subspecies. Interbreeding can, however, lead to the production of sterile males in significant numbers or it may be that all the male members of interbreeding subspecies are sterile. This will lead to the development of a second stage of speciation in which subspecies are distinguishable as incipient species. These semispecies no longer mate and produce offspring from the original gene pool. The natural selection process will have sorted the members of the original species into subspecies and then into semi-species and then into new species.

These new species may look very much alike in morphology and in behavior, but they will no longer mate and no longer share the same gene pool. When this happens, a new set of species will have evolved. It may be the case that the subspecies that evolves into a new species will survive, but the members of its “cousins” in the other subspecies from which it emerged will not survive as separate species because they were not successful in adapting to the changing environment. These older and nonadaptive species will die out or become extinct. Nature is filled with the fossils of extinct species from earlier times.

Speciation may occur because of geographic separation. The rise and fall of mountains, of islands, or the drifting of continents can lead to geographic separation in which the populations undergo changes into new species from original common ancestors. The process of adaptive radiation may also occur as new niches occur in the environment. The Galapagos Islands has finches that Charles Darwin and others have studied that exhibit changes because of adaptive radiation.

When a species undergoes a rapid process of development in reproductive isolation, chromosomal mutations may occur in one part of the isolated population. The mutant population may then interbreed with its original parent population. Their offspring can be successful as new species or in many cases will be hybrids that are sterile and are thus pruned from off of the evolutionary tree.

In plants, a quantum speciation can occur that creates the form of speciation called polyploidy. The effect is to create the beginning of a new species in just a few generations. It occurs because at the gamete state of cell division, abnormal cells develop four sets of chromosomes instead of the normal two sets inherited from two parents. Self-fertilization adds the additional sets of chromosomes in the flowering stage. The resulting hybrids will be able to be reproductively active, but will not be able to reproduce with the original parent species because the changes have made it reproductively isolated.

Extinction of species can also occur because the members of a species become too specialized in the foods they eat or in a behavior. Or they may not reproduce in sufficient numbers to sustain their population or may have lost a specialized habitat.

Besides the fossil evidence for speciation, there are now genetic studies that show species arise without great morphological changes. The use of DNA is enabling researchers to trace the genealogical linage of species back to often long-extinct common ancestors.

There are problems with the idea of speciation defined in part as a breeding population. There are life forms that are asexual or that engage in self-fertilization. These life forms violate the criterion of interbreeding. As a result, these species are defined in terms of their morphology or physiological resemblances to other members of their population group. There are also cases of populations of crossfertilizing organisms. Their species cannot be determined experimentally and can only be recognized by characteristics. These forms of organisms are a challenge to the whole idea of using species as a unit of classification.

Controversy

Philosophical issues have been a part of the use of species as a basic classifying unit. Some of these issues arose among the Greeks and have gained new life in the modern world. For Plato and Aristotle, the species were fixed. The Platonic theory of forms or species was that they were eternal and unchangeable. They were ideas or the forms of things that were mixed with matter to create the visible objects in the visible world. To Aristotle, a philosopher who sought after the forms in the objects of the world by collecting specimens of shellfish at ancient lakes, forms were unchangeable and inherent in the visible objects of the world. Aristotle used the term species to designate natural species, which he studied and described in his natural history.

The idea of the fixity of the species was current in Europe prior to the publication of The Origin of the Species by Charles Darwin in 1859. A few decades previously, some theologians had adopted the Aristotelian idea of the fixity of the species as the correct interpretation of the meaning of the Biblical description in Genesis that says that God created each plant and animal “after its own kind.” The idea of the changeability of the species through an evolutionary process was taken by many as a challenge to the veracity of scripture rather than a challenge to the thinking of Aristotle. The adherence to the idea of the fixity of the species has been a characteristic of fundamentalist and other Christian groups that have rejected an evolutionary model for describing the great biological diversity of the earth.

Bibliography:

Michael T. Ghiselin, Metaphysics and the Origin of Species (State University of New York Press, 1997);
Jody Hey, Genes, Categories, and Species: The Evolutionary and Cognitive Cause of the Species (Oxford University Press, 2001);
Michael A. Huston, Biological Diversity: The Coexistence of Species (Cambridge University Press, 2002);
Harold Mooney and Richard J. Hobbs, eds., Invasive Species in a Changing World (Island Press, 2000);
Matt Ridley, Genome: The Autobiography of a Species in 23 Chapters (HarperCollins Publishers, 2000);
Dov F. Sax, Steven D. Gaines, John J. Stachowicz, and Steven Gaines, eds., Species Invasions: Insights into Ecology, Evolution, and Biogeography (Sinauer Associates, Inc., 2005);
Randall T. T. Schuh, Biological Systematics: Principles and Applications (Cornell University Press, 2000);
David N. Stamos, The Species Problem: Biological Species, Ontology, and the Metaphysics of Biology (Rowman & Littlefield Publishers, Inc., 2003);
Don E. Wilson and DeeAnn Reeder, Mammal Species of the World: A Taxonomic and Geographic Reference (Johns Hopkins University Press, 2005);
Edward O. Wilson, Diversity of Life (W.W. Norton, 1999);
Judith E. Winston, Describing Species: Practical Taxonomic Procedure for Biologists (Columbia University Press, 2005).