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habitat or respond to changing condi- 
tions with billions of individuals. Also, 
because microorganisms are haploid, 
mutations are expressed, and genetic 
adaptations tested, immediately. 
There is another aspect to the poten- 
tial benefit of a pollen selection system. 
George Williams of the State Univer- 
sity of New York at Stony Brook and 
V.C. Wynne-Edwards of the University 
of Sussex have asked what are the con- 
tributions that sexual reproduction 
makes to the process of adaptation. 
Granting that it provides new and pos- 
sibly adaptive genetic combinations, 
they point out that sexual reproduction 
also has a negative effect. The sexual 
process takes two perfectly good genet- 
ic types (good enough, that is, to sur- 
vive to, and perhaps through, the rigors 
of parenthood) and scrambles them to- 
gether, risking the loss of the good qual- 
ities of both parents. Williams and 
Wynne-Edwards suggest that unless 
populations are huge, on the order of 
tens of millions of individuals, sexual 
reproduction may cost more than it 
gains. Here is where pollen tube compe- 
tition may become important. 
In both angiosperms and gymno- 
sperms, for each individual that reaches 
maturity, large numbers of seedlings 
are started. However intense this selec- 
tion among seedlings may be, the angio- 
sperms, as we have seen, possess yet 
another level of selection. Pollen tube 
competition may mean that the angio- 
sperms, when compared with the gym- 
nosperms, are relatively free to 
recombine genetic types, and that the 
selected products of this recombination 
are quite certain to possess a reasonably 
well-balanced, vigorous gene set. The 
gymnosperms, lacking the opportunity 
for intensifying pollen tube selection, 
would be forced to adopt a relatively 
conservative genetic system, one that 
preserves adaptive genetic types rather 
than producing vast numbers of new 
adaptations. 
Intense pollen tube competition, an 
accidental consequence of the shift 
from wind to insect pollination, may 
thus have granted the angiosperms 
carte blanche for genetic experimenta- 
tion. This evolutionary plasticity may 
have led early and often to adaptive fea- 
tures, rare or absent within the gymno- 
sperms, that enabled the flowering 
plants to reach their present position of 
dominance in the world’s flora. 
David L. Mulcahy is a professor in the 
Botany Department of the University of 
Massachusetts at Amherst. 
Ydu never forget 
your firstGirl. 
