Biological Classification: Kingdom Animalia

Origin of life: Even the oldest human observation (like the Rig Vedic period of India) recorded in history, supports the thought that most primordial life forms might have began in water only.
(reference: pictures 1, 2 & 3 of a hymn from Rig Veda shown are in old Sanskrit language text translated in Hindi & English).

Later Miller-Urey experiment (1952-53) and Oparin proved it so in laboratory conditions for the modern mind.
Primordial Soup: This first life form, sort of naked protoplasm kind of thing took the shape, which was named Cell by Robert Hooke (1665) and life began to grow and took a route of simple to complex forms, towards two major branches, as animal and plant cell.
(reference: picture 4, 5 & 6).

Need of Classification: As number of life forms were in millions with much variety, a need arose to name and classify them. As we all know the credit goes to Carolus Linnæus a Swedish botanist, physician, and zoologist, father of modern taxonomy. Credit for Binomial nomenclature also goes to Linnæus. The application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are the International Code of Zoological Nomenclature (ICZN) for animals and the International Code of Botanical Nomenclature (ICBN) for plants.
(reference picture: 7, 8 & 9)

System of Classification and their Units: All the types of classifications proposed & followed from Linnaeus (1735) to Cavalier-Smith (2004) follow almost the same domain name of units as: Kingdom-Phylum-Class-Order-Family-Genus-Species.
(reference picture: 11, 12 & 13)

Interesting Evolutionary Trend: The classification patterns followed is so interesting that this itself is an Evidence in the support of Darwin's theory of Organic Evolution.
As we move from base of the classification, we find the life forms they them self are arranged in simpler to complex forms like: Unicellular Prokaryote-Unicellular Eukaryote- Multicellular Tissue level- Multicellular organ level- Multicellular Organ System level.
(reference picture: 14)