We’ve all heard of the five kingdoms of life, but a few decades ago a new type of bacteria that caused the reorganization of life into three domains was discovered. Supported by genetic analysis, domain classification system is replacing the five kingdoms of life.
Previously, the organization for five kingdoms coexisted with another classification of two general groups: prokaryote and eukaryote. But more recently, scientists realized that the system of the five kingdoms is no longer adequate.
Classification domains was proposed by Carl Woese because of two events. First, in the seventies several new species of organisms that live in extreme environments such as hot springs, acidic lakes, etc., where it was believed that there could not be any living organism were discovered. These bacteria and organisms seemed “archaea” is called, which means “ancient bacteria”.
It is controversial whether viruses should be included because viruses do not meet the seven characteristics of living things.