Another approach, “Top-Down,” uses current taxa to infer the nature and timing of the origin of life on Earth. To do so, we take current examples of life on Earth and trace their ancestry, by comparing the nearly hundred shared genes, primarily associated with biological translation (Koonin 2011). All life shares a last universal common ancestor, “LUCA” for short. There may have been several origins of life, but our evidence is insufficient to distinguish this scenario from a single origin. Nevertheless, at least one origin, presumably in Earthly pre-biotic conditions, led to the existence of LUCA, an important constraint upon theorizing about the origin of life. It is widely expected that LUCA was merely one creature in a larger population and existed long after the origin of the first organism. There are also a variety of concerns with respect to LUCA: whether it was simple or complex (Mariscal &amp; Doolittle 2015); whether it had a membrane that resembled any of the current membranes (Koonin 2011); whether the genes it contained were ancestors of our own genes or subsequently acquired (Doolittle &amp; Brown 1994, Woese &amp; Fox 1977; Woese 1998); whether its genome was made of DNA (Forterre 2006a), whether it was a heterotroph or autotroph; where it lived; and when it lived.