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b. Potential long-term evolutionary consequences 
Section IV-A of this EIS describes the mechanisms by which DNA 
segments may be moved from one organism to another, either within 
a given species or between species. As pointed out there, natural 
recombinations across species lines have been observed between a 
limited number of microorganisms. Natural recombination between 
single -celled organisms such as those used as host cells in recombinant 
DNA experiments and more complex animals and plants has not been 
observed. 
It has been suggested that the latter recombinations do not, or 
cannot, occur (17, 18) or else occur very seldom (19). Further, it has 
been argued that the formation of recombinants between distantly 
related species in the laboratory, and the accidental release of such 
recombinants into the biosphere, might lead to unpredictable evolu- 
tionary consequences (17, 19). Because the detailed processes of 
evolution are not well understood, the nature of those possible con- 
sequences has not been and cannot be described. Similarly, no 
mechanism by which a recombined DNA would alter evolution has been 
suggested. 
On the other hand, it has been argued that evolutionary consequences 
of recombinant DNA research are not likely to be serious (20). This 
argument states that natural recombinations between distantly related 
species are probably more frequent than available data would suggest- - 
that there is no 'barrier' between prokaryotes and eukaryotes. Natural 
recombinants have not been observed because no one has looked for 
them. Opportunities for such recombination are frequent in nature, 
since prokaryotes live in close proximity to and, in some instances, 
within cells of eukaryotes. And given the likelihood that such recom- 
binants will usually be at a selective disadvantage (see Section IV-C-l-a 
of this EIS), they would be short-lived and hard to find. The argument 
concludes that man-made recombinants are probably not novel and 
are not likely to lead to novel evolutionary consequences. 
The Guidelines recognize this issue by requiring stricter contain- 
ment for experiments involving organisms not known to exchange DNA 
in nature than for those involving organisms known to do so (Section 
III-B-2-ii of the Guidelines). But the indefinite and remote nature of 
the concern indicates that more restrictive action is unwarranted. 
c. Other considerations 
The foregoing descriptions of the kinds of possibly hazardous situations 
that might arise from organisms obtained through recombinant DNA 
experiments must be considered in the light of certain more general 
issues. 
