Falta de capacidade evolutiva nas redes autocatalíticas autosustentadoras: uma limitação no 'metabolismo primeiro' na origem da vida

Lack of evolvability in self-sustaining autocatalytic networks: A constraint on the metabolism-first path to the origin of life

Vera Vasas a,b, Eörs Szathmáry a,b,c,1 and Mauro Santos a,d

- Author Affiliations

aCollegium Budapest, Institute for Advanced Study, H-1014 Budapest, Hungary

bInstitute of Biology, Eötvös University, H-1117 Budapest, Hungary

cParmenides Center for the Study of Thinking, Munich D-80333, Germany

dDepartament de Genètica i de Microbiologia, Grup de Biologia Evolutiva, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain

Edited by Gerald F. Joyce, The Scripps Research Institute, La Jolla, CA, and approved December 3, 2009 (received for review November 3, 2009)

Abstract

A basic property of life is its capacity to experience Darwinian evolution. The replicator concept is at the core of genetics-first theories of the origin of life, which suggest that self-replicating oligonucleotides or their similar ancestors may have been the first “living” systems and may have led to the evolution of an RNA world. But problems with the nonenzymatic synthesis of biopolymers and the origin of template replication have spurred the alternative metabolism-first scenario, where self-reproducing and evolving proto-metabolic networks are assumed to have predated self-replicating genes. Recent theoretical work shows that “compositional genomes” (i.e., the counts of different molecular species in an assembly) are able to propagate compositional information and can provide a setup on which natural selection acts. Accordingly, if we stick to the notion of replicator as an entity that passes on its structure largely intact in successive replications, those macromolecular aggregates could be dubbed “ensemble replicators” (composomes) and quite different from the more familiar genes and memes. In sharp contrast with template-dependent replication dynamics, we demonstrate here that replication of compositional information is so inaccurate that fitter compositional genomes cannot be maintained by selection and, therefore, the system lacks evolvability (i.e., it cannot substantially depart from the asymptotic steady-state solution already built-in in the dynamical equations). We conclude that this fundamental limitation of ensemble replicators cautions against metabolism-first theories of the origin of life, although ancient metabolic systems could have provided a stable habitat within which polymer replicators later evolved.

autocatalysis graded autocatalysis replication domain model units of evolution

Footnotes

1To whom correspondence should be addressed. E-mail: szathmary@colbud.hu.

Author contributions: V.V., E.S., and M.S. designed research; V.V., E.S., and M.S. performed research; V.V. and M.S. analyzed data; and V.V., E.S., and M.S. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

This article contains supporting information online at www.pnas.org/cgi/content/full/0912628107/DCSupplemental.

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