Our knowledge of the genetic and biochemical basis of evolution centered on DNA enables us to understand the unity of life on earth. DNA provides the molecular continuity that connects us and all other organisms to our distant ancestors—anaerobic microorganisms living around 3.5 billion years ago. But before the last universal common ancestor (LUCA), where did the DNA come from? How do we connect the primordial chemical soup of small biochemically important molecules produced in the classic Miller-Urey experiment to the complex macromolecules in our earliest ancestors? The "warm little pond" envisioned almost 150 years ago by Darwin for the origin of life may have some relevance, but it was pure speculation with little empirical evidence. While we may never know the actual path to life, constructing scientifically reasonable models for the process has occupied great minds and has narrowed the conceptual gap. As Francis Crick wrote, "to show no interest in the subject is to be truly uneducated." In recent years, consensus has developed around the RNA World hypothesis as the precursor and one step in the evolution of our DNA World. I will review the evidence for that hypothesis based on projecting back in time from existing life and highlight some of the major conceptual challenges that remain in generating a reasonable model for the emergence of the biosphere from the inorganic world of the geosphere.
Hal White Bio:
Prior to his recent retirement, Hal White earned his living as a Professor of Biochemistry in the Department of Chemistry and Biochemistry where he worked since 1971. Much of his research, teaching, and natural history pursuits have been motivated by an encompassing interest in evolution ranging from the molecular to the organismal. As a high school student, he roamed the woods of central Pennsylvania, worked part time in a Drosophilagenetics lab, and first read Darwin's Origin of Species. Later his research focused on comparative biochemistry of dehydrogenase enzymes and the evolution of vitamin-transport proteins. He was one of the first people to recognize the possibility of an RNA World. Throughout his career at the University of Delaware, he taught a course in Biochemical Evolution. He served on the editorial board of the Journal of Molecular Evolution for 20 years.