**Systematics** is the branch of biology that deals with classification, nomenclature and taxonomy. Carolus Linnaeus states that two names are applied to organism (internationally) i.e Generic and Specific name. **Biological classification** is the study of the bio-diversification of living forms (past and Present) and their relationship among living things through time.
Systematics is defined as the entire field of study which deals with the kind of organisms, their distribution, classification and evolution. Simpson (1966) defined systematics as the scientific study of the kinds and diversity of organisms and of the relationship that exist between them. The arrangement of organisms into categories that express their phylogeny based on information such as structure, development, physiological function and evolutionary history of organism is known as **Biological Classification.**

**Phylogeny** is the hypothetical relationship between organisms being compared. Phylogeny tree is also known as phylogeny. Phylogeny tree is a diagram that depicts the line of evolutionary descent of different species, organisms or genes from a common ancestors. 

![1199px-Phylogenetic_tree.svg.png](https://images.hive.blog/DQmV3JHs92G8KJX3DP69CKXUf2SLfisTm4LtPrYB7TETzjD/1199px-Phylogenetic_tree.svg.png)
<center>[Phylogenetic tree](https://upload.wikimedia.org/wikipedia/commons/7/70/Phylogenetic_tree.svg)</center>
The important/purpose of phylogeny tree is to provide a clear and practical way to organize information about organism. It also shows relationship between the ancient and modern group, indicate the evolutionary descent by which the modern day group may have developed and provide a basis for comparing animal group. The principle intends to bring in knowledge or update us on the present classification that organism share a common genetic heritage in their DNA are closely related to each other than to any other group of the same rank. However, this classification system are modified as ideas of their phylogeny change.

## HISTORY Of BIOLOGICAL CLASSIFICATION
History of biological classification. Those that contributed to the classification are:
ARISTOTLE (384-322BC)
JOHN RAY (1627-1705)
CAROLUS LINNAEUS (1707-1778)
R.H WHITTAKER (1950)
ERNEST HAEKEL

### Aristotle (384-322BC)
Aristotle is known as the father of biological classification. His classification skill referred to readily apparent group such as whales, fishes, bats and birds. He recognizes the need for group and group name of organism. He classified the type of creatures based on similarity. i.e Animal with blood and animal without blood, Aquatic and terrestrial organism were also classified. His view of life was hierarchical. He assumed that organism should be classified from the lowest to the highest and human species being the highest.

### John Ray (1627-1705)
John Ray uses anatomical differences as the prime criterion for bringing out the resemblance and differences among group, e.g lung breathing and Gill breathing. It is still a preferred method in classify organism. John Ray recognized that variation in organism
may because by genotypic and phenotypic factors. He classified more than 20,000 plants and animals. His highly descriptive strategy distinguished animals by their hooves, nails, flocks, teeth and toes. Yet, his inability to see microscopic distinction placed him to classify Algae, Lichen, Fungi and Coral together. A lichen is a compound organism that contain an Alga and a Fungus but Coral is an animal. The standard universal binomial nomenclature for species is attributed.

### Carolus Linnaeus (1707-1778)
He applied the method of classification consistently to plant as in planetarium in 1753 and to animal in system naturae in his tenth edition in 1758. Linnaeus system was readily applicable to charle's Darwin New concept of evolution which is published in his book in 1859. Charle's Darwin propose the theory that organism evolve from the process of natural selection. This classification system do not have effect on the existing classification but provide a new explanation nearness of descent for the natural grouping of organism. This approach is fundamental to modern classification scheme.

**LINNEAN SYSTEM**
Linnaeus change classification category as a series of nested sets. His sequence from broadest to smallest is kingdom, class, order, genus and species. Relationship between each species is determined by the many shared characteristics and he stressed on especially those that have to do with substance, digestion and feeding. Species is given a unique two parts name in Latin and the name is always underline or italicized in print or written. The name consist of genus which is a group of species more closely related to
one another than to any other group followed by the specific name which identifies a particular species within the genus. The first letter of the genus is capitalized while the specific name is in lower case letter as in Homo sapiens (Human) and Sciurus carolinensis (Grey squirrel).

### R.H Whittaker (1950)
He classified organism based on prokaryotic (single celled) or Eukaryotic (composed of one ormore cell). He proposed the five kingdom of classification.
These are:
* Kingdom Monera
* Kingdom fungi
* Kingdom protists
* Kingdom plantae
* Kingdom Animalia

### Ernest Haeckel
 He represented phylogeny as a means of training and branching diagram further sophisticated improvement and a new biological outlook e.g ecological, geographical and morphological characteristics. Haeckel is a German zoologist, artist, marine biologist, professor, musician e.t.c. He classified thousand of plants and animals. He discovered and name thousand of new species.

He practiced and formularized Charle's Darwin law and develop the influence but no longer widely based on the calculation theory (ontogeny to recapitulate phylogeny) claiming that an individual organism undergo evolutionary development or phylogeny. Theory of recapitulation is called bio-genetic law or embryological parallelism often expressing Earnest Heackeal phase. Ontogeny recapitulate phylogeny is the historical hypothesis that the development of embryo from fertilization to gestation or hatching both two stages representing or resembling a successful adult stage in the evolution of animal from a remote ancestor (phylogeny). It was formulated in 1820 based on the work of Joan Mecken.

A species is a group of organism that are capable of interbreeding and reproducing a fertile Offspring in nature. The genetic differences between species are:
* Differences in Anatomy
* Behaviour 
* Ecology
* Physiology
* Cellular chemistry.