"Ur-organism" is the term loosely given to the hypothetical "first life" species, from which all other life presumably evolved. The term was used first by Charles Darwin

Charles Darwin

Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...

, and has been picked up by various subsequent thinkers addressing the same questions of origin of species. Not to be confused with the Last universal ancestor

Last universal ancestor

The last universal ancestor , also called the last universal common ancestor , or the cenancestor, is the most recent organism from which all organisms now living on Earth descend. Thus it is the most recent common ancestor of all current life on Earth...

 (LUA), the term "ur-organism" refers to the first universal ancestor common to all life existing on earth today. It is therefore the ancestor of the LUA.

The ur-organism is not necessarily the first instance of life arising abiogenically

Abiogenesis

Abiogenesis or biopoesis is the study of how biological life arises from inorganic matter through natural processes, and the method by which life on Earth arose...

 on Earth. As with the concept of the "Mitochondrial Eve

Mitochondrial Eve

In the field of human genetics, Mitochondrial Eve refers to the matrilineal "MRCA" . In other words, she was the woman from whom all living humans today descend, on their mother's side, and through the mothers of those mothers and so on, back until all lines converge on one person...

, "the existence of the ur-organism does not imply the existence of a population bottleneck

Population bottleneck

A population bottleneck is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing....

 or a first organism. It is estimated to have lived some 3.9 to 4.1 billion years ago.

See also

• Abiogenesis
  Abiogenesis
  Abiogenesis or biopoesis is the study of how biological life arises from inorganic matter through natural processes, and the method by which life on Earth arose...
  
  
• Aleksandr Oparin
  Aleksandr Oparin
  Alexander Ivanovich Oparin was a Soviet biochemist notable for his contributions to the theory of the origin of life, and for his authorship of the book The Origin of Life. He also studied the biochemistry of material processing by plants, and enzyme reactions in plant cells...
  
  
• Last universal ancestor
  Last universal ancestor
  The last universal ancestor , also called the last universal common ancestor , or the cenancestor, is the most recent organism from which all organisms now living on Earth descend. Thus it is the most recent common ancestor of all current life on Earth...
  
  
• Common descent
  Common descent
  In evolutionary biology, a group of organisms share common descent if they have a common ancestor. There is strong quantitative support for the theory that all living organisms on Earth are descended from a common ancestor....