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The effect of foreign DNA on the survival of recipient species is 
important to the discussion of possible hazards of recombinant DNA 
experiments. A recipient species may acquire a potential for harmful 
effects as a result of the foreign DNA, but the possibility of the occur- 
rence of the harmful effects will depend on the survival of the altered 
recipient and its ability to multiply. If acquisition of foreign DNA 
increases the probability of survival and multiplication, the possibility 
of harmful effects will increase. Similarly, if acquisition of foreign 
DNA decreases the probability of survival or multiplication, the pos- 
sibility of harmful effects will decrease. It is important to recognize, 
in evaluating the potential for harmful effects, that significant 
infections of animals and plants by bacteria or viruses usually require 
contact with far more than a single organism. The critical number 
of infectious agents will vary, depending on both the agent and the 
recipient. 
Survival of Host Cell . There are multiple indications that both 
host bacteria - and plasmid or virus vectors containing inserted foreign 
DNA are less likely to survive and multiply than are the original 
organisms, except for the very unusual instances where the foreign 
DNA supplies some function, such as antibiotic resistance, that favors 
the organism in a particular, non-natural environment.* Natural 
selection results in the survival of only well-balanced and efficient 
organisms; unneeded genetic material tends to be lost. Essential 
functions are carefully controlled and are switched on and off as 
needed. The activity of a particular gene product depends upon, 
and in turn influences, many other functions of a cell. It is unlikely 
that uncontrolled, nonessential properties such as might be introduced 
by foreign genes would result in any advantage to the survival and 
multiplication of an otherwise well-balanced organism. Similarly, 
it is unlikely that elimination of a normal gene product caused 
by insertion of a foreign DNA sequence would be advantageous. More 
likely than not, any new properties derived from insertion of foreign 
DNA would confer some relative disability to the recipient organism. 
Therefore, it is probable that bacterial cells, plasmids, or viruses 
containing inserted foreign DNA would multiply more slowly in nature 
than the same cells or vectors without foreign DNA; and in a natural 
competitive environment, those organisms containing recombinant 
DNA would generally be expected to disappear. For bacterial hosts, 
the rate of disappearance would depend on the rate of growth relative 
to that of competing bacteria. The following calculation demonstrates 
this point. 
*See reference 10 for a general discussion of the analysis in this 
paragraph. 
