Robert Shapiro

Scientific American, June 2007; Cover and pages 24-31

Summary: The sudden appearance of a large self-copying article such as RNA was exceedingly improbable. Energy-driven networks of small molecules afford better odds as initiators of life.

Brief overview: The idea that life began with small molecules (sometimes called "metabolism-first") has circulated for decades, but has received little attention because of the popularity of another theory. In the more-favored theory the origin of life involved the appearance, by chance, of a very large molecule that could copy itself ("RNA-first"). In this article I summarized the arguments that support the former position. A longer, more technical version was published in 2006 in the Quarterly Review of Biologh, Volume 81, pages 105-125, under the title "Small Molecule Interactions Were Central to the Origin of Life."

The key requirements needed to start life (as listed in the Scientific American article) were:
1. A boundary is needed to separate life from nonlife.
2. An energy source is needed to drive the organization process.
3. A coupling mechanism must link the release of energy to the organization process that produces and sustains life.
4. A chemical network must be formed to permit adaptation and evolution.
5. The network must grow and reproduce.

The dispute between these two theories has broad implications. I can quote the last two paragraphs of the Scientific American article:

If the general small-molecul paradigm were confirmed, then our expectations of the place of life in the universe would also change. A highly implausible start for life, as in the RNA-first scenario, implies a universe in which we are alone. In the words of the biochemist Jacques Monod: “The universe was not pregnant with life nor the biosphere with man. Our number came up in the Monte Carlo game.”

The small molecule alternative, however, is in harmony with the views of biologist Stuart Kauffman: “If this is all true, life is vastly more probable than we have supposed. Not only are we at home in the universe, but we are far more likely to share it with as yet unknown companions.”