LUCA – Analizando a versão acadêmica (de LUA)

Estou estudando o excelente paper abaixo, acho que um dos mais completos sobre a matéria. O paper pode ser visto em:

The Universal Ancestor

  1. Carl Woese*

+ Author Affiliations

  1. Department of Microbiology, University of Illinois at Urbana-Champaign, B103 Chemical and Life Sciences Laboratory, MC-110, 601 South Goodwin Avenue, Urbana, IL 61801
  1. Contributed by Carl R. Woese

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A genetic annealing model for the universal ancestor of all extant life is presented; the name of the model derives from its resemblance to physical annealing. The scenario pictured starts when “genetic temperatures” were very high, cellular entities (progenotes) were very simple, and information processing systems were inaccurate. Initially, both mutation rate and lateral gene transfer levels were elevated. The latter was pandemic and pervasive to the extent that it, not vertical inheritance, defined the evolutionary dynamic. As increasingly complex and precise biological structures and processes evolved, both the mutation rate and the scope and level of lateral gene transfer, i.e., evolutionary temperature, dropped, and the evolutionary dynamic gradually became that characteristic of modern cells. The various subsystems of the cell “crystallized,” i.e., became refractory to lateral gene transfer, at different stages of “cooling,” with the translation apparatus probably crystallizing first. Organismal lineages, and so organisms as we know them, did not exist at these early stages. The universal phylogenetic tree, therefore, is not an organismal tree at its base but gradually becomes one as its peripheral branchings emerge. The universal ancestor is not a discrete entity. It is, rather, a diverse community of cells that survives and evolves as a biological unit. This communal ancestor has a physical history but not a genealogical one. Over time, this ancestor refined into a smaller number of increasingly complex cell types with the ancestors of the three primary groupings of organisms arising as a result.

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Biologists have long subscribed to the powerful, unifying idea that all life on Earth arose from a common ancestor (1). Nothing concrete could be said about the nature of this ancestor initially, but it was intuitively assumed to be simple, often likened to a prokaryote, and generally held to have had little or no intermediary metabolism (2). Only when biology could be defined on the level of molecular sequences would it become possible to seriously question the nature of this ancestor.

The unrooted universal phylogenetic tree that emerged from ribosomal RNA (rRNA) sequence comparisons provided the first glimpse of our ultimate ancestor,

( com o tempo vamos acrescentando aqui a critica sob o ponto de vista da Teoria da Matriz/DNA)

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