Κλάδος: Διαφορά μεταξύ των αναθεωρήσεων

| page = 217 }}</ref> In principle, the ancestor is an individual, but in [[Sexual reproduction|sexually reproducing]] species, there will always be at least two ancestors, and in virtually all instances there will be an influx of genes from the rest of the [[gene pool]] in the descendant lines. The individual ancestor is thus often a theoretical construct, and in practical terms the ancestor of a clade of sexual organisms is a set of [[species]] or in the best cases a [[population]]s. The common ancestor of any group of reasonable size and most of that ancestor's descendants have typically been long extinct.<ref group=note>This may not be true in very small and recent clades, where the common ancestor and all descendants are still living.</ref> It is not necessary for a clade to contain any living representatives.