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Darwin and Microbiology

For the Darwin bicentennial, microbiologists examine how their research continues to elucidate evolution
Roberto Kolter and Stanley Maloy Roberto Kolter is Professor of Microbiology and Molecular Genetics at Harvard Medical School, Boston, Mass., and Stanley Maloy is Professor of Biology, San Diego State University, San Diego, Calif. Galapagos Islands, August, 2009.Charles Darwin spent a few weeks during September and October of 1835 exploring the Galapagos Islands. His observations during that time reverberate deeply in the history of science because the features of the plants and animals that Darwin saw there contributed greatly to the development of his ideas of evolution by natural selection. Of these islands he remarked in the Voyage of the Beagle (1939):"The natural history of this archipelago is very remarkable: it seems to be a little world within itself. . ." But compared to the myriad microscopic worlds present in every handful of Galapagos soil that Darwin set foot on, the archipelago would not be a "little world within itself" but a vast universe containing countless worlds of unimaginable diversity. For every grain of soil, every drop ofwater of our planet is rich with microbial life that lies there, waiting to be discovered. It is this vast unknown that led Edward O. Wilson, probably the most highly regarded naturalist alive today, to end his Pulitzer-winning autobiography Naturalist with the following lines: "If I could do it all over again, and relive my vision in the twenty-first century, I would be a microbial ecologist. Tenbillion bacteria live in a gram of ordinary soil, a mere pinch held between thumb and forefinger. They represent thousands of species, almost none of which are known to science. Into that world I would go with the aid of modern microscopy and molecular analysis. I would cut my way through clonal forests sprawled across grains of sand, travel in an imagined submarine through drops of waterproportionately the size of lakes, and track predators and prey in order to discover new life ways and alien food webs. All this, and I need venture no farther than ten paces outside my laboratory building. The jaguars, ants and the orchids would still occupy distant forests in all their splendor, but now they would be joined by an even stranger and vastly more complex living world virtually withoutend."

Indeed there are "forests of bacteria" in a grain of sand. How can one come to understand the working of these "forests of bacteria" that cannot be perceived through direct observation? Ecologists that venture into tropical rain forests seek understanding in two ways. First, they tabulate the species present. Second, they investigate the interactions among those species as accurately aspossible. In doing so, their aim is to develop models that allow them to predict how such forests might respond to changes. Ideally, we would like to pursue the investigation of the "forests of bacteria" in similar ways. That is a daunting task at present because we are just beginning to get a glimpse of how extremely complex the microbial world really is! Just attempting to tabulate the number ofspecies present in any given location reveals this remarkable complexity. Yet, describing

how we learned to tabulate the number of extant bacterial species will illuminate the dramatic change in worldview-regarding the planet's biodiversity-that we have undergone in the last 30 years. Already during Darwin's time naturalists were cognizant of the need to determine the relationship among species asa first step in understanding their ecology and evolution. To do so, they compared visible characteristics of each organism with other. The classic example that comes to mind about this is the comparison of the various species of finches that Darwin noted inhabited different islands in the Galapagos archipelago. Comparing the lengths and widths of the finches' beaks, it was possible to obtain a...
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