Health and Disease 
to me that natural selection is an adequate way to account for 
these various survivals, even at the molecular level. 
Huxley: Yes. Szent-Gyodrgyi said he couldn’t understand 
it happening by mutation. Of course nobody can understand it 
by mutation alone. Mutation is merely the raw material; it is 
natural selection that does the guiding and screening. 
Szent-Gyérgi: But one mutation wouldn’t do; you must 
have many more simultaneously, or the whole system would no 
longer fit together. Then on top of all this, there is an addi- 
tional complication: if the body has to build a substance, say 
protein X, it cannot do so directly. It must first have a factory 
which can turn out protein X; that is, it has to build the nucleic 
acid system into which it has to code the blueprint for protein X. 
All this becomes so complicated that I am unable to form a 
clear picture of how it all can happen. That is the mystery to 
me; maybe you understand it better. 
Crick: I think you are a neo-vitalist, Dr. Szent-Gyérgyi, 
and it is characteristic of the neo-vitalist that he says he isn’t! 
You made a great number of provocative statements, and apart 
from your remark on the hierarchies of organization, I think I 
disagree with almost everything you said, although I enjoyed 
your paper very much. Take, for example, the argument about 
the importance of quantum mechanics: I don’t believe that a 
large new field relevant to chemistry remains to be discovered. 
Our basic knowledge of physics and chemistry is, I think, 
sufficiently complete for much of biology, though this is admit- 
tedly a very dangerous statement to make. Secondly, the argu- 
ment about the amount of complexity is grossly exaggerated. 
The atomic nucleus is certainly extremely complex, and we do 
not in fact understand it, but the effect of changing the mass of 
the nucleus of an atom (a change which leaves its chemical 
properties intact) is extremely slight. Therefore, what one 
wants to know is, what are the significant alternatives involved, 
not just how complicated an atom is to put together. It 
also seems to me that mutation and natural selection 
are very powerful, and are potentially capable of explaining 
evolution. 
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