The most recent common ancestor is the furthest internal node that connects two or more tips/groups. You’ll often see Most Recent Common Ancestor abbreviated as MRCA.

Lets take a very simple example using a phylogeny of the Vipers.

A phylogeny of vipers. Tips read from top to bottom: Corn Snake, Saw Scale Viper, Puff Adder, Bushmaster, Fer-De-Lance, Eyelash Viper, Rattlesnake, Cottonmouth, Copperhead

 

If we zoom in on Copperheads (Agkistrodon contortix) and Cottonmouths (Agkistrodon piscivorous), we find their most recent common ancestor is at the node highlighted here in Red.

A phylogeny. Tips read top to bottom: Rattlesnake, Cottonmouth, Copperhead. A red dot is found at the node connecting cottonmouths and copperheads

 

But know that it doesn’t have to be just the tips of a phylogeny! We can also do entire groups of organisms. For example, the figure below shows the MRCA highlighted in red for all rattlesnakes and the group containing Copperheads and Cottonmouths (otherwise known as the “Agkistrodon genus”).

 

A phylogeny. Tips read from top to bottom: Rattlesnake, CottonMouth, Copperhead. A brown box highlights the Cottonmouth and Copperhead tips as well as their most recent common ancestor. Text below the group reads Genus: Agkistrodon. A red dot is found at the node connecting rattlesnakes with the Agkistrodon group

Last modified: Thursday, 27 November 2025, 8:18 AM