Classical taxonomy divides living beings and inanimate objects of nature into kingdoms, composed successively of phyla, classes, orders, families, genera and so on until reaching species.

This way of ordering nature presented a very static image. It did not explain where or how the genera within a family or the species within a genus had originated.

The way of giving an explanation was achieved with the introduction of the term CLADO.

The etymology tells us that CLADO comes from the Greek term CLADOS κλαδιa or κλάδος, which means branches and which in biology can be used as a group of beings that includes a common ancestor and all its descendants (extinct or currently alive).

Thus, when explaining the process of the appearance of new species, we can use the term cladogenesis (origin of the CLADES) which in classical taxonomy would be appropriate to interpret as the origin of the species.

But if we go the other way, from a current or previous species, backwards passing from the branches to the trunk, we will undoubtedly end up with the term L.U.C.A. (Last Universal Common Ancestor) that is, the individual that through the process of cladogenesis has given rise to all the living beings currently alive or extinct.

But at this stage of the reasoning the doubt arises as to whether there was a single L.U.C.A. or whether at some point there was a CLADE of L.U.C.A.