A freak event created the ancestor of all multicellular life on Earth. Without this unconventional genesis, we might never have become more than bacteria
Life is what you make of it. For the first organisms on the newly watery Earth, that was little. For a billion years or more, single-celled entities simply morphed, multiplied and colonised the oceans. Photosynthesis was one innovation: from about 2.5 billion years ago, blooms of sea bacteria supplied Earth's atmosphere with its first whiff of oxygen. But when the next turning point came, it was in a rather unexpected direction.
Life on Earth stands either side of a chasm. On one side are the prokaryotes - bacteria and archaea - whose simple cells are not much more than tiny bags of chemicals. On the other are the eukaryotes, whose complex cells have internal membranes, skeletons ...