25 
Assume that a new organism constitutes 90 percent of 
a population, but grows 10 percent less rapidly than its 
natural counterpart. The new organism will drop from 
a concentration of 90 percent to a concentration of 0.0001 
percent (1 part in 1,000, 000) in 207 generations. If the 
generation time of the natural organism is one hour, 
this decline in concentration will occur in about 8-1/2 
days. 
Although unlikely, there is a chance that a bacterial host of 
recombinant DNA will grow more rapidly than if it were lacking 
the foreign DNA, especially if the cells encounter new environments 
in which the new gene provides some adaptive advantage. (The 
calculation given above can also be applied. ) A relevant example 
of such a situation can be found in the rapid and widespread increase 
in the resistance of bacteria to clinically important antibiotics during 
the last 20 years. It is well known that such resistance is genetically 
determined and occurs by natural recombination, and genes specifying 
resistance have been described (11). Furthermore, it is well known 
that such genes may be transferred, by natural DNA recombination, 
from one species of microorganism to another (11). In this instance, 
the foreign DNA may significantly enhance the survival rate of a 
bacterial recipient whose environment contains the antibiotic in 
question, while cells sensitive to the drug will be destroyed. Thus, 
increased use of antibiotics to cure or prevent infectious disease 
has been accompanied by increased prevalence of organisms resistant 
to these antibiotics. 
The ability of recipient bacterial host cells to survive and multiply 
might also be enhanced by acquisition and expression of a foreign gene 
conferring the ability to metabolize a particular nutrient. In an environ- 
mental niche containing the nutrient, such a recombinant might compete 
successfully against organisms native to the niche. Thus, not only 
an important nutrient there might be destroyed, but any beneficial 
functions performed by native organisms could be lost upon the 
successful establishment of the recombinant in the niche. 
These two examples serve to illustrate some of the complexities 
involved in determining whether the insertion of a given fragment of 
foreign DNA will be advantageous or disadvantageous to the recipient 
organism: the nature of the inserted genes, the nature of the environ- 
ment, and the relation between the two must be considered. However, 
this analysis is necessarily simplistic. In the absence of the highly 
specific relationships that are, for example, apparent in the case of 
antibiotic resistance, very little is understood about how the totality 
of the genetic make-up of a given organism or species contributes 
to its competitive advantage even in a defined ecological niche. Modern 
evolutionary theory does not provide useful frameworks for analysis. 
There are in fact current major controversies concerning the role of 
natural mutations in evolution, and the same questions are relevant 
to the issues raised by recombinant DNA research. 
