Page 156 - Once Upon a Time There Was Darwinism

And Edward S. Deevey, a bi-
ologist and ecologist at the
University of Florida, points out

that there is a limitation to vari-
ation in nature: "Wheat is still
wheat, and not, for instance,
grapefruit; and we can no
Once Upon a Time There Was Darwinism
Lo ren Eis ley
more grow wings on pigs
than hens can make cylin-
drical eggs." 105

Experiments conducted on fruit flies
also struck the wall of "genetic limitation." In all of
these experiments, fruit flies underwent changes to a certain
extent, but beyond that limit, no change was observed. Ernst
Mayr, a well-known neo-Darwinist, reports from two experi-
ments done on fruit flies:
In the starting stock, the combined average bristle number of
males and females on these segments was about 36. Selection
for low bristle number was able to
lower this average after 30 genera-
tions to 25 chaetae, after which the
line soon died out owing to sterility.
. . In the "high line" (selection for
high bristle number), progress was
at first rapid and steady. Within
20 generations bristle number
had risen from 36 to an aver-

Ernst Mayr

154