Taxonomy
There are many kinds of living organism having different properties in the earth. Scientist state that there are approximately 10 million types of living organism. As I said before, biology deals with living things however, it is difficult to examine 10 million different organism one by one. Thus, scientists decided to organize them according to their common properties.History of Classification
Organizing living things according to their common properties is called taxonomy. Aristotle is the first scientist who group organism under two titles; plant and animals and they have also subtopics. Picture given below summarizes taxonomy of Aristotle.
As you can see from the schema, he groups living things according to their appearances and medium they live. Classification done by only appearances of living things is called empirical classification. It is not a scientific classification method.
However, in 17th century John Ray stated that organisms having similar properties should be in same group. For example, not all living things in water are fish or all flying things are bird.
Today species can be defined as, kinds of fertile living things having similar properties.
In 1707-1778, Carl Von Linnaeus used binomial nomenclature for grouping species. This naming method gives information about genus and species (or epithet) of living things.
Example:
Homo sapiens : Human
Canis lupus : Wolf
Felis domesticus: House Cat
Felis tigris: Tiger
Pinus nigra: Black Pine
We use capital letter while writing first letter of genus and use small letters while writing complimentary name as given in the examples above.
Example: Which ones of the following species show similar properties?
I. Capra domesticus
II. Felis domesticus
III. Canis lupus
IV. Felis leo
Answer:
The first word of the genre name indicates the genus to which it belongs. In this case, both living things called Felis domesticus and Felis leo are more similar to each other since the genus name is Felis.
Taxonomic Categories
In the classification of living things, organisms take place in hierarchical groups, from small to large and covering more species. Classification units from small to large are listed as follows.Species → Genus → Family → Order → Class → Phylum → Kingdom → Domain
Species: It is the basic classification unit.
Genus: It is the step formed by the combination of similar species.
Family: It is the step formed by the combination of similar genera.
Order: It is the step formed by gathering similar families.
Class: It is the step formed by the gathering of similar orders.
Phylum: It is the step formed by the gathering of similar classes.
Kingdom: It is the step formed by the gathering of similar phylums.
| House cat | Human | |
| Kingdom | Animalia | Animalia |
| Phylum | Chordata | Chordata |
| Class | Mammalia | Mammalia |
| Order | Karnivora | Primates |
| Family | Felidae | Hominidae |
| Genus | Felis | Homo |
| Species | Felis domesticus | Homo sapiens |
Since there will be an increase in the number and variety of individuals as we go from the species to the domain, the similarities of individuals decrease while their differences increase. As the individuals move from the domain to the species, similar individuals will increase, the common features increase and the different features decrease.
Phylogenetic Classification
Phylogenetic classification is a form of classification that is based on the evolution of organisms, their anatomical similarities, protein similarities and evolutionary steps. Today, biologists use this type of classification. While determining the classification units, scientists make use of branches such as homology, analogy and physiology.Homology: Organs with the same origins but different functions are called homologous organs. The branch of science that studies these organs is called homology. The arm of the human, the wing of the bird are homologous organs.
Analogy: Organs with different origins and same functions are called analogue organs. The branch of science that studies these organs is called analogy. The cat's leg and the fly's leg are analog organs. Although their task is the same, it appears that their evolutionary origin is completely different when examined.
Physiology: The branch of science that explains the functions of organs and tissues in the organism based on the rules of physics and chemistry is called physiology.
The Original Author: Mrs. Şerife (Erden) SARICA
