MUTAGENS OF POTENTIAL SIGNIFICANCE 215 



Goldstein: Then I make the assumption that the DNA's of all species 

 are equal, or at least the genetic effects on all species are about the 

 same. Without this assumption, I can do nothing, because the only 

 data that we have to work with are on bacteria and Drosophila. If we're 

 going to make any first approximations to man, we're going to have to 

 do it by assuming that the susceptibility to the mutagenic effect is the 

 same in man as in these other species. I don't believe this assumption 

 for one moment, but as a first approximation — 



Benzer: You can cross that one out, too. Nobody else believes it, 

 either. 



Neel: If you cross that one out, you would have to cross out quite 

 a few extrapolations about radiation effects. Are you willing to cross 

 them out? 



Auerbach: No. 



Novick: The genetic material is the same in both cases, specifying 

 the exact nature of these events. 



Neel: Would you accept that correction — the genetic material? 



Goldstein: Yes. I was trying to say, if we are to make any calcula- 

 tion at all, we must forget for the moment possible differences in 

 susceptibility to caffeine between bacteria and Drosophila and man; 

 otherwise, we would be talking about — 



Lederherg: The listing of assumptions in this fashion lets you 

 inquire where the biases might come in. That could include the best 

 judgment you can make of the final conclusion. If you have no infor- 

 mation that suggests that this ought to be modified in one direction or 

 another, with respect to the final conclusion, we will all agree this is a 

 statement about which there is considerable doubt. But we are unable 

 to say whether we are making an over- or an underestimate of the 

 final result. I think, however, it is important to expose where the 

 biases might be, by making assumptions of this kind. 



Auerbach: The second assumption does seem doubtful; as far as we 

 know at present, caffeine produces mutations in bacteria and not in 

 Neurospora. 



Lederherg: Are you prepared to suggest whether human DNA is 

 more or less susceptible to caffeine than bacterial DNA? 



Goldstein: To emphasize what Josh says, I have made assumptions 

 which I know are false, as well as assumptions about which there are 

 doubts, precisely for the purpose of putting down on paper what the 

 assumptions have been that underlie any calculation one is going to 

 make. 



On the one hand, we have data on the mutagenic effect of caffeine in 



