Submitted on: 18 May 2010.
Revised on: 22 June 2010.
Accepted on: 28 June 2010.
QUARTERLY REVIEW OF BIOLOGY---UNIV CHICAGO PRESS
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Submitted on: 24 May 2010.
Revised on: 17 June 2010.
Accepted on: 11 July 2010.
QUARTERLY REVIEW OF BIOLOGY
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