Changing Environments 2,
the sequel


Reality rarely, if ever, has constant conditions

  • if it is consistent,
    . . . -it is by limits on its variability
    . . . -it has a variance

  • I suspect that actual environmental conditions
    . . . -vary as a complex series of additive cycles
    . . . . . ranging from very short (minutes to hours)
    . . . . . to very long (thousands to millions of years)

    The critical issue in adaptation is the relative lengths of:

  • species generation time, compared to
  • environmental cycle return period

  • if generation time long relative to cycle time
    . . -environment appears to alternate between two alternative values
    . . -species adapts by maintaining genetic diversity
  • if cycle time long relative to generation time
    . . -environment appears to exhibit trends
    . . -species adapts by following the trend


  • {AA, Aa, aa} = {wAA*p2, wAa*2pq, waa*q2}
  • this time w is function of environment
    . . . w = G(X)



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    © 2004 Prof. LaFrance, Ancilla College