Andrew Knoll

Life On A Young Planet

Wandering through an alpine forest or snorkeling above a coral reef, we observe an ecology shaped by plants (or seaweeds) and animals, with large vertebrates at the top of the food chain and other creatures below. Ecosystems also contain many organisms that we can't see, but concern for their contributions is generally fleeting—surely bacteria and other microorganisms, tiny and simple, eke out their living in a world of our making?

As large animals, we can be forgiven for holding a worldview that celebrates ourselves, but, in truth, this outlook is dead wrong. We have evolved to fit into a bacterial world, and not the reverse. Why this should be is, in part, a question of history, but it is also an issue of diversity and ecosystem function. Animals may be evolution's icing, but bacteria are the cake.

Plants, animals, fungi, algae, and protozoa are eukaryotic organisms, genealogically linked by a pattern of cell organization in which genetic material occurs within a membrane-bounded structure called the nucleus. Bacteria and other prokaryotes are different—their cells lack nuclei. In terms of biological importance, eukaryotes would seem to have a decisive edge; eukaryotic organisms display a variety of form that ranges from scorpions, elephants, and toadstools to dandelions, kelps, and amoebas. In contrast, prokaryotes are mostly minute spheres, rods, or corkscrews. Some bacteria form simple filaments of cells joined end to end, but very few are able to build more complicated multicellular structures.