Components of a coalescence tree
A coalescence tree
works backward in time. This tree has nine Leaf nodes, corresponding to
the nine contemporary individual sampled in the current
generation. Each leaf node is connected by an External lineage to its MRCA
with the next most closely related entity, typically
another leaf node, or sometimes a group: cf. Leaf node #7
from the left. These connections occur at Internal nodes. Internal lineages connect
these Internal nodes (which are also MRCAs
for their groups) into successively more inclusive groups.
Note that all leaf nodes with a common MRCA are more
closely related to each other than they are to any
other leaf node. Ultimately, all sampled individuals will coalesce
into a single MRCA at the base of the tree.
The existence of a common MRCA at any particular point in time does not imply that that individual was the only individual alive at that time.The existence of the human mitochondrial DNA "Eve", a particular woman who lived about 200,000 years in East Africa as the coalescent maternal ancestor of all human beings, is a powerful meme of the essential unity of the human species. In some minds, the idea 'coalesced' with the "Eve" in the creation stories of the Book of Genesis, which is an incorrect reading of the Book of Genetics.
The existence of a common MRCA at any particular point in time does not imply that that individual was the only individual alive at that time.The existence of the human mitochondrial DNA "Eve", a particular woman who lived about 200,000 years in East Africa as the coalescent maternal ancestor of all human beings, is a powerful meme of the essential unity of the human species. In some minds, the idea 'coalesced' with the "Eve" in the creation stories of the Book of Genesis, which is an incorrect reading of the Book of Genetics.
Figure © 2013 by Sinauer; Text material © 2022 by Steven M. Carr