We are constantly confronted with the concept of species criteria in life - determining the types of flowers in a flower bed or fish in an aquarium. Very useful may be the ability to distinguish between the species of edible mushroom and poisonous. But, despite the apparent simplicity of this concept, in biology, the criteria for a species and the very concept of “species” remain the most ambiguous.
Historical excursion
The very concept of “species” has existed in the concept of people since ancient times. For a long time, by a species was meant a group of homogeneous objects or objects meeting the criteria of the species. Examples: types of kitchen appliances (frying pan, pot, cauldron) and types of ducks (pintail, teal and mallard). This term was introduced into biology by Karl Linney - under the guise of he understood constant, discrete (different), objectively existing groups of living organisms. At that time, a typological approach prevailed in biology - the selection of the species was based on several external characteristics.
Today, this approach has remained in biology as a morphological criterion for a species. With the accumulation of knowledge in biochemistry, genetics, biogeography and ecology, the requirements for the classification and systematization of all living things on the planet expanded. In modern biology, by the term understand the group of organisms (populations), in which individuals can freely interbreed and produce prolific offspring. In this case, the main criterion for a species is the impossibility of crossing them with representatives of other species.
Why this approach is not applicable
But not for all living organisms, this approach in determining the species affiliation is applicable. The species criterion based on reproductive isolation is not applicable to organisms that reproduce asexually and by parthenogenesis. The first includes all prokaryotes (prenuclear, bacteria), the second - only a few eukaryotes (nuclear), such as rotifers. It is incorrect to apply the term “species” to extinct animals.
Typology Change Evolution
In 1859, an event occurred that changed the worldview of naturalists and biologists. Charles Darwin’s work, “The Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life,” saw Charles Darwin's work. The author considered the concept of “species” artificial and introduced for convenience.
The advances in genetics and the development of the theory of evolution have led to the fact that species of organisms are determined not by differences, but by their similarity or the general gene pool. Now a species is a collection of populations with a geographical and ecological community, capable of free crossbreeding, and having similar morphophysiological characters.
Extension of the definition of the concept
Today, many species criteria are used to systematize the position of the body. Each deep-sea ocean trawl lifts new creatures from the depths, which biologists are trying to put into the general system of the organic world on the planet. At the same time, a lot of view criteria are used, and this work is not as easy as it might seem. But for widespread use in biology, the main criteria of the species are used, which we all studied at school. We will focus on them.
Classification of species criteria in biology
Species criteria in biology are considered to be traits inherent in only one species. The combination of these characteristics determines the species affiliation of the body. The main criteria for the species are:
- Morphological - the totality of all similar features in the structure of the body. It includes all material structures: from chromosomes to the structure of organs, systems and appearance.
- Physiological - the similarity of all the vital processes of organisms of one species. It is at this level that the reproductive isolation of representatives of one species in relation to others is usually fixed.
- Biochemical - this criterion includes the specificity of proteins and nucleic acids, as well as the specificity of enzymatic processes.
- Ecological and geographical - sometimes this criterion is divided into two separate ones. It characterizes the territory of a certain type of residence.
- Genetic - based on a unique set of hereditary material of the species, its quality and structure.
Fractional unit of life organization
The main feature of the species is the community of the gene pool of its representatives. The unity of the species and its historical stability is ensured by free crossing, which maintains a constant flow of genes within the species. At the same time, the gene pool of the species is constantly changing as a result of mutations, recombinations and natural selection, which becomes the source of the emergence of new species in the process of evolution. Therefore, the species exists, figuratively speaking, only at the moment strictly observed by us.
Types of species
Description of new species is associated with a mismatch of the criteria of already known species - one or more. First of all, the morphological and genetic criterion is taken as the basis for the description of the species . The first draws parallels between external characters, and the second focuses on the genotype. In this regard, the following species species are distinguished in biology:
- Monotypic species - all characters, including external ones, are common to all representatives of the species.
- Polytypic species - individuals within a species can have various phenotypes (external qualities), which directly depend on the environment of their habitat. In this case, the taxonomy uses the category “subspecies”.
- Polymorphic species - in this case, there are several morphoforms (groups of individuals with different colors or other characters) inside the species that freely interbreed.
- Double species. These are species that are morphologically similar, inhabit the same territory, but do not interbreed with each other. About this concept in more detail later.
- "Half-species", borderline cases - sometimes the process of speciation gives a group of organisms signs that change the status of the group. This is a rather difficult category in taxonomy and often the selection of a species as a semi-species meets a lot of controversy among specialist biologists.
Intraspecific diversity
Most species of living organisms on the planet are polymorphic. Many insects (bees, termites, ants) have developed working polymorphism. Inside the species, females, males and working individuals are distinguished. Such categories are called "castes."
Under the influence of various environmental factors, ecological polymorphism arises. In deer beetles there are males with different lengths of mandibles - their development is directly related to the development conditions of the larva. Under the influence of seasonal factors, seasonal polymorphism occurs when different generations of the same species differ from each other. For example, in the variegated butterfly (Araschnia levana), the generation born in early spring has red wings with black spots, and the summer generation has black wings with white spots.
An example of polymorphism in the biological species Homo sapiens is the presence of four blood groups, a variety of colors of hair and skin colors. That is why all racial prejudices have no biological validity, since all people on the planet are just different morphoforms of a single species, Homo sapiens, and all human races are on the same biological level of development. Indisputable evidence of this statement are interracial marriages, as well as the presence of talented artists and scientists among representatives of all races and nationalities.
Doubles in nature
Not too common in nature is the existence of two species on the same territory, very similar in appearance, morphology and anatomy, but incapable of interbreeding with each other. Most often, such species are found among those animals that choose a sexual partner by a specific criterion, for example, by smell (insects or rodents) or by the acoustic characteristics of singing (birds).
An example of double species is the fact that we call malaria mosquitoes 6 species of outwardly identical insects that differ in the shape and color of the eggs.