Last Common Ancestor

This cladogram shows that the LCA of beetles and flies is more ancient than the LCA of moths and flies. It does not, however, indicate which of the branches represents the original line and which represents the branching species.

A Last Common Ancestor (LCA) is a term given to the most recent common ancestor of any two clades, for example species that came to be separated by a species barrier.

LCA of three 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 600 million 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 — 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 0.5 percent of the male population in the world, or roughly 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, the term MRCA has come to include an ancestor within a species — for example, a common grandfather — rather than a cross-species ancestor. For example, 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. But there have not been any speciation events in Homo sapiens during the past 3,000 years, so this person cannot have been the LCA with any other species.

See also

• Y-chromosomal Adam
• Mitochondrial Eve
• Most Recent Common Ancestor
• Last universal ancestor
• Cladistics
• Phylogenetic tree
• Genetic genealogy
• Genealogical DNA tests
• Founder effect
• Piltdown man
• Lowest common ancestor
• Urbilaterian, the conjectured last common ancestor of bilaterian animals

References

• About the last common ancestor, the universal life-tree and lateral gene transfer
• Modern African Ape Populations as Genetic and Demographic Models of the Last Common Ancestor of Humans, Chimpanzees, and Gorillas
• Recent African Origin of Modern Humans Revealed by Complete Sequences of Hominoid Mitochondrial DNAs
• Estimating the age of the last common ancestor of extant primates using the fossil record