 The founding ecological geneticists dismissed any significant role for random genetic drift in evolution (see the entry on  genetic drift).  The theoretical interaction of random genetic drift and natural selection for single genes with constant effects can be seen in  Figure 1.  Fisher in his evolutionary theory  assumed that natural populations achieved or sustained very large  sizes as seen in his correspondence with S. Wright (letter from  R. A. Fisher to S. Wright, August 13, 1929, as quoted in Provine  1986: 255) where he stated that “I believe N must  usually be the total population on the planet, enumerated at sexual  maturity”. Similarly, according to his intellectual biographer  W. Ewens: 