Last universal common ancestor

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The last universal common ancestor of all cells (LUCA, progenote) is an evolutionary concept none the less relevant to medicine as it defines what all cellular life presently in the biosphere has inherited from a common ancestral cell. Between two or more species the genetic term that is used to define the identical ancestors point (IAP) is the last common ancestor (LCA). The similar concept applied to homo sapiens defines the Y chromosomal Adam and the mitochrondrial Eve although as this is a single species the correct genetic term to use is most recent common ancestor (MRCA). Due to the complexities of inheritance some paradoxes with respect to the LCA and MRCA concepts are possible. Whatever the concept is inconsistent with there being a first couple (Adam and Eve) for any organism as at the time of any MRCA or LCA there is a population of organisms that could exchange genetic information and some of those organisms could still be contributing to part of the genome of at least one organism in the current comparison, but not all. As of 2016 it is understood that RNA[1] and a small number of critical proteins ( about 355) [2] define this phylogenetic inheritance of the LUCA.