Hierarchy of classification

Hierarchy refers to organization system in which groups are nested in each level. Higher levels are the most general and contain a collection of groups and so on down each level to the most specific. Biological classification is a hierarchy from general groups (such as domains) down to specific groups (genus and species).
Hierarchy of classification
Kingdom
Phylum
• Sub-phylum
• Super-class
Class
• Sub-class
• Super-order
Order
• Sub-order
• Super-family
Family
• Sub-family
Genus
• Sub-genus
Species
• Sub-species

There is a specific hierarchy by which all living things are classified
example of the hierarchy - classification of the house cat:

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Felidae
Genus: Felis
Species: Felis domesticus

Classification of Humans
Kingdom Animalia :
Usually motile, multi-cellular organisms, without cell walls or
chlorophyll; usually, internal cavity for digestion of nutrients
Phylum Chordata:
Organisms that at one time in their life history have a dorsal
hollow nerve cord, a notochord, and pharyngeal pouches
Class Mammalia:
Warm-blooded vertebrates possessing mammary glands; body
more or less covered with hair; well-developed brain
Order Primates:
Good brain development, opposable thumb and sometimes big
toe; lacking claws, scales, horns, and hoofs
Family Hominidae:
Limb anatomy suitable for upright stance and bipedal locomotion
Genus Homo:
Maximum brain development, especially in regard to particular
portions; hand anatomy suitable to the making of tools
Species Homo sapiens:
Body proportions of modern humans; speech centres of brain
well developed

What is a species: special problems for paleontology
A group of individuals that interbreeds.
A group of individuals that shares a common set of genetic characteristics .