From humanity's point of view, one of the most important events in history was the evolution of the eukaryotic cell-the sort from which people's bodies are made. Without this innovation, which happened about 2 billion years ago, life on Earth would consist only of bacteria and a group of similarly simple creatures called archaea. Plants and animals, not to mention algae, fungi and myriad single-celled organisms like amoebae, would never have come into existence. Even today, bacteria and archaea are probably more important than eukaryotes to the smooth running of the biosphere. But because they are invisible to the naked eye, they are easily overlooked. Eukaryotes are what people think of when they think of living things.
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