Most Recent Common Ancestor - MRCA of Different Species

MRCA of Different Species

Further information: Last universal ancestor, List of concestors in The Ancestor's Tale

It is also possible to use the term MRCA to describe the common ancestor of two or more different species. In the past, the term MRCA was used interchangeably with last common ancestor (LCA) to denote both the common ancestor within a species and that between species. But MRCA is now more frequently used to describe common ancestors within a species. On the other hand, LCA now describes the common ancestor between two species.

The concept of the last common ancestor is described in Richard Dawkins' book, The Ancestor's Tale, in which he imagines a 'pilgrimage' backwards in time, during which we humans travel back through our own evolutionary history and as we do so are joined at each successive stage by all the other species of organism with which we share each respective common ancestor. Dawkins uses the word "concestor" (coined by Nicky Warren) as an alternative to LCA.

In The Ancestor's Tale, following the human evolutionary tree backwards, we first meet the concestor which we share with the species that are our closest relatives, the chimpanzee and bonobo. Dawkins estimates this to have occurred between 5 and 7 million years ago. Another way of looking at this is to say that our (approximately) 250,000-greats-grandparent was a creature from which all humans, chimpanzees and bonobos are directly descended. Further on in Dawkins' imaginary journey (imaginary, in that the journey is going backwards in time), we meet the concestor we share with the gorilla, our next nearest relative, then the orangutan, and so on, until we finally meet the concestor of all living organisms, known as the last universal ancestor.

A common mistake made by the public as well as some authors is to refer to a proposed last common ancestor as an earliest ancestor. Examples include the book The Link: Uncovering Our Earliest Ancestor by Colin Tudge, and a documentary of the same name screened on the History Channel (US) and BBC One (UK), both referring to the primate fossil dubbed Ida.