NASA Astrobiology Institute (NAI)

My project is exploring philosophical issues in astrobiology. My central focus this year was on the origin of life: what is the proper level of analysis for a successful theory of the origin of life? Among other things, I compared and contrasted contemporary scientific theories of the origin of life in light of what philosophers of science have learned about the structure and justification of scientific theories.

Theories of the origin of life may be roughly classified as metabolism-first theories (e.g., Wächtershauser, de Duve, Segre & Lancet, and Kauffman), genes-first theories (e.g., Woese, Orgel, Joyce, and Cairns-Smith), and co-origin theories (e.g., Dyson, and Copley). The question is what is the proper level of analysis for such a theory. I discovered that although these theories are sometimes portrayed as rivals, they are neither logically nor empirically incompatible but rather pitched at different levels of explanation. For example, theories of the origin of life and theories of the nature of life can cut across each other in important ways. “Metabolism-first” theories might be true for the origin of life despite the fact that the capacity to reproduce and transmit to progeny adaptive modifications in structure are more important to the nature of life than the capacity to self-organize and maintain self organization. Similarly “genes-first” theories might be true for the origin of life despite the fact that the capacity to self-organize and maintain self-organization is more fundamental to the nature of life than the capacity to store and transmit hereditary material. Interestingly, this theme is reflected in different versions of the RNA world. What unites them all under the rubric “RNA world” is not a commitment to RNA (or an RNA-like precursor) preceding peptides but the idea that the latter can’t by itself qualify as life. One important issue that is sometimes ignored is that RNA doesn’t qualify as a “genes-first” view unless it actually “codes” for something, and it isn’t clear that a community of self-catalyzing RNA molecules can be described as “coding” for better replicators any more than a “compositional genome” can be characterized as “coding” for a self-reproducing chemical network; the concept of a gene in origin of life theories is not clearly defined. Finally, theories of the origin of life often assume that there is only one causal pathway for the emergence of life but this isn’t true of other chemical phenomena, and there is little reason to suppose that it is true of life. Different environmental conditions produce different chemistries (e.g., energy gradients and molecular building blocks). Under one set of environmental conditions, gene-like structures might emerge first, followed by metabolic networks, and under another metabolic networks might emerge first, followed