If we trace the Tree of Life to the base of its trunk, we find the Last Universal Common Ancestor (LUCA): a single-celled, bacterium-like organism that is the distant progenitor of all living things, humans included. This one shared antecedent is the reason why everything from blue whales to giant redwoods to bacteria have inherited common features such as DNA to store genetic information and a molecule called ATP that is the universal source of energy.
