with very low complexity due to their error-prone translation apparatus ("noisy genetic transmission channel"), which produced high mutation rates that limited the specificity of cellular interaction and the size of the genome. This early translation apparatus would have produced a group of structurally similar, functionally equivalent proteins, rather than a single protein. Furthermore, because of this reduced specificity, all cellular components were susceptible to horizontal gene transfer, and rapid evolution occurred at the level of the ecosystem. The transition to modern cells (the "Darwinian Threshold") occurred when organisms evolved translation mechanisms with modern levels of fidelity: improved performance allowed cellular organization to reach a level of complexity and connectedness that made genes from other organisms much less able to displace an individual's own genes. In later years, Woese's work concentrated on genomic analysis to elucidate the significance of horizontal gene transfer (HGT) for evolution. He worked on detailed analyses of the phylogenies of the aminoacyl-tRNA synthetases and on the effect of horizontal gene transfer on the distribution of those key enzymes among organisms. The goal of the research was to explain how the primary cell types (the archaeal, eubacterial, and eukaryotic) evolved from an ancestral state in the RNA world. Perspectives on biology Woese shared his thoughts on the past, present, and future of biology in Current Biology: The "important questions" that 21st century biology faces all stem from a single question, the nature and generation of biological organization. . . . Yes, Darwin is back, but in the company of . . . scientists who can see much further into the depths of biology than was possible heretofore. It is no longer a "10,000 species of birds" view of evolution—evolution seen as a procession of forms. The concern is now with the process of evolution itself. I see the question of biological organization taking two prominent directions today. The first is the evolution of (proteinaceous) cellular organization, which includes sub-questions such as the evolution of the translation apparatus and the genetic code, and the origin and nature of the hierarchies of control that fine-tune and precisely interrelate the panoply of cellular processes that constitute cells. It also includes the question of the number of different basic cell types that exist on earth today: did all modern cells come from a single ancestral cellular organization? The second major direction involves the nature of the global ecosystem. . . . Bacteria