Genealogic Tree and its Root LUCA

at the molecular level, biological evolution is — at least in part — about changes in the primary structures of biopolymers. 

An important thing for physics is that a DNA double helix s shape does not really depend very much on the sequence of monomers. (This is because the pairs are mutually complementary and are hidden inside the double helix.) In this sense, DNA is like a piece of paper or a computer memory — a media suitable for recording any message. It is for precisely this reason that the DNA texts can be altered. Otherwise, the result of evolution would be not the best suited organisms, but merely DNA molecules with lower energy. In contrast, the tertiary structures of proteins strongly depend on their primary structures this allows different proteins to carry out so many different functions, and does not allow proteins to serve as inheritable information storage. 

Typically sequences of DNA and the set of sequences of proteins do not change during the life time of a particular cell, but changes do occur infrequently, from time to time, due to mutations, rephcation errors, and other mechanisms. What does it lead to  

Large scale sequencing of biopolymers and the growth of corresponding rich data bases produced an unprecedented wealth of data to address the genetic closeness of various species or even different individuals. 

The idea of LUCA started to crystallize in 1960s, when genetic code was cracked and turned out to be universal in all of the biosphere (with some marginal variations) — that was naturally interpreted as a sign of common ancestry. Now the idea of LUCA seems well established, although genetic and other features of it are not yet clear. 

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