He labeled the trunk Moneres, by which he seems to have meant the simplest of single-celled organisms, resembling bacteria. (For technical reasons, their name, meaning “single,” was later corrected to Monera.) This hypothesis, among his three, was the boldest application of Darwinian theory that could be made at the time. It asserted that all living creatures, including humans, have descended from some common ancestor resembling a bacterium. But in 1866 and for some years after, Haeckel himself was still undecided about which of his three hypotheses was correct.
