[Marxism] complexity and mobility

Andrew Pollack acpollack2 at yahoo.com
Wed Nov 29 10:23:41 MST 2006


What's  particularly intriguing about this study is not just the rise of new  and more complex life forms after a catastrophic event, but the impact  of a particular style of life -- mobility, and thus interaction with  other kinds of life -- on the nature of that complexity.
  I think it would be productive to look at this scenario through the  framework of Niles Eldredge's schema of how different levels of the  genetic and ecological hierarchies in evolution interact.
  
  http://www.nytimes.com/2006/11/28/science/28mari.html?_r=1&oref=slogin
  
  
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  November 28, 2006
        Marine Life Leaped From Simple to Complex After Greatest Mass Extinction          By ANDREW C. REVKIN
                  At least five mass extinctions,  most presumably caused by asteroids that struck the earth, have  transformed global ecology in the half-billion years since the  emergence of multicelled life, lopping entire branches from the  evolutionary tree and allowing others to flourish. 
  The greatest “great dying,” 251 million years ago, erased 95 percent  of species in the oceans (and most vertebrates on land). But new  research suggests that it was followed by an explosion of complexity in  marine life, one that has persisted ever since.
  Moreover, it happened quite suddenly, according to the study, which  was led by scientists at the Field Museum of Natural History in Chicago  and published  in the current issue of the journal Science. The shift to complicated,  interrelated ecosystems was more like a flip of a switch than a slow  trend.
  The researchers detected the change by analyzing records of marine  fossils from 1,176 sites around the world, which are part of a new  international archive, the Paleobiology Database (pbdb.org).
  They found that marine life before the biggest global die-off, the  Permo-Triassic extinction, was evenly split into two types of  communities: simple ones, in which most species were anchored in place  and got by without interacting with neighbors (like eating them or  being eaten by them), and complex ones, with many interrelationships.
  But since then, complex communities filled with grazers, scavengers,  predators, burrowers and other mobile creatures have been three times  as common as simple ones, said Peter J. Wagner, the lead author of the  study. 
  The shift essentially took the oceans from a norm in which anchored  (or sessile) creatures, including brachiopods and sea lilies, filtered  food carried in currents to one dominated by roaming (or motile) fauna  like snails, urchins and crabs.
  Dr. Wagner said it was not clear why this particular extinction  spasm had this permanent effect on the character of communities, while  others did not. 
  A 2002 study led by Richard K. Bambach, an emeritus professor at Virginia Tech,  found the general shift to a higher abundance of motile fauna from the  early Triassic Period onward, but it did not examine patterns in  individual communities.
  But Dr. Wagner said motility was an enduring characteristic of the more variegated biological webs.
  “The increased diversity of mobile species would have contributed to  more complex ecological communities,” he said. “With sessile guys,  everybody is just living next to one another and that’s it. With  mobility and higher metabolism, you bump into each other more often,  both literally and figuratively, and you end up with a greater number  of potential interactions.”
  Wolfgang Kiessling, a paleoecologist at Humboldt University in  Berlin who assessed the study in an accompanying article in Science,  said it represented “a major step forward,” particularly in finding a  reliable way to distinguish simple ecosystems from complex ones through  500 million years of life history.
          
      
  
 
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