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The universal ancestorA 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.
Document ID
Document Type
Reprint (Version printed in journal)
External Source(s)
Woese, C. (University of Illinois at Urbana-Champaign, B103 Chemical and Life Sciences Laboratory MC-110, 601 South Goodwin Avenue, Urbana, IL 61801, United States)
Date Acquired
August 22, 2013
Publication Date
June 9, 1998
Publication Information
Publication: Proceedings of the National Academy of Sciences of the United States of America
Volume: 95
Issue: 12
ISSN: 0027-8424
Subject Category
Distribution Limits
NASA Discipline Exobiology
Non-NASA Center