Last Common Ancestor

Last Common Ancestor (LCA) is the most recent common ancestor of two populations that came to be separated by a species barrier.

LCA of two species


The more distantly related two species are, the more ancient their LCA will be. The LCA of elephant and earthworm, for example, lived an ancient two billion years ago. The LCA of two more similar species, the elephant and the tyrannosaurus, lived three hundred million years ago, while the LCA of the elephant and mammoth, two closely related species, lived only seven million years ago.

Other common ancestor titles
Last Universal Ancestor (LUA) or Last Universal Common Ancestor (LUCA), or either name without the "Last", are the names given to the hypothetical and controversial unicellular organism or single cell that gave rise to all life on Earth three to four billion years ago.

Mitochondrial Eve: DNA studies show human mitochondria can trace their lineage to a “mitochondrial Eve”, the matrilineal most recent common ancestor for all humans alive today, who lived approximately 150,000 years ago.

Y-chromosomal Adam: DNA studies show that all Y chromosomes in currently living men are descended from a “Y-chromosomal Adam”, the patrilineal most recent common ancestor for all humans alive today, who lived approximately 60,000 years ago.

Concestor: Term coined by Richard Dawkins as a possible replacement for "Last Common Ancestor."

Common ancestor: Any two species have millions of plain “common ancestors”. The ancestors of the elephant and mammoth, for example, were common to both animals for billions of years &mdash; up to their split seven million years ago, this being the date of their last common ancestor.

The term "common ancestor" is often used in a lineage sense, which is different from the species sense discussed here. You and your cousin have three grandfathers between you, one of whom is a "common" grandfather. You share a great grandfather with your second cousins, and share a great great great great great grandfather with perhaps a thousand of your 6th cousins. It has been estimated that Genghis Khan is a common grandfather to some 16 million men.

“Most Recent” Common Ancestor: Until 1999 the terms “Last” and “Most recent” common ancestor had been used more or less interchangeably. In papers published since then, however (Rohde, Olson, and Chang; see reference, below), the term MRCA has come to mean a particular ancestor within a species &mdash; for example, a common grandfather &mdash; rather than the species’ founder. Computer simulations suggest that every person living today could share a common ancestor who lived as few as 2,000 to 3,000 years ago. This person (name lost to history) has been entitled the Most Recent Common Ancestor (MRCA) of All Mankind.