Before enzymes and templates: theory of surface metabolism.

Woese's three kingdoms (161-166) constitute the deepest branching of the known biosphere. His suggestion to search for a common ancestor has led to the present hypothesis. It is proposed here that, at an early stage of evolution, there are precursor organisms drastically different from anything we know. These organisms are acellular and lack a mechanism for division, yet they can grow. They possess neither enzymes nor a mechanism for translation, but they do have an autocatalytic metabolism. They do not have nucleic acids or any other template, yet they have inheritance and selection. Although they can barely be called living, they have a capacity for evolution. Central to the proposed theory is the idea that life at this early stage is autotrophic (cf. reference 53) and consists of an autocatalytic metabolism confined to an essentially twodimensional monomolecular organic layer. These surface organisms (surface metabolists) are anionically bonded to positively charged surfaces (e.g., pyrite) at the interface of hot water. The adherence to the positively charged mineral surface is not the result of adsorption ( as suggested by Bernal [6] in his clay theory) but rather of in situ autotrophic growth of anionic constituents acquiring their surface bonding in statu nascendi. Instead of adsorption, the organism is faced with desorption, that is, a selective detachment of its constituents. This means a negative selection favoring higher anionic bonding strength. Large polyanionic constituents with ever stronger surface bonding are automatically selected: first, polyanionic coenzymes, and eventually nucleic acids and polypeptides. The primitive surface metabolists grow by spreading onto vacant surfaces; they reproduce by