412 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



is converted to oxygen by a similar process. In this and other known 

 ways all the elements are formed. As one goes up the scale, the 

 number of possibilities rapidly increases. As elements begin to inter- 

 act to give inorganic molecules, the number of possibilities becomes 

 still greater. I do not know how many inorganic molecules are pos- 

 sible, but I do know there must be a very large mmiber. With organic 

 molecules the number becomes truly enormous, particularly with large 

 molecules like proteins and nucleic acids. For example, there are 

 something like 4 raised to the 10,000th power ways a modest-sized 

 DNA molecule can be made. There appears to be no stage at which 

 there is a true qualitative change in the nature of evolution. The 

 number of possibilities goes up gradually, the complexity goes up 

 gradually, and there appears to be no point at which the next stage 

 cannot be reached by simple mutation. 



Let us suppose we have a small piece of DNA protected by a protein 

 coat and capable of replication in the presence of the proper building 

 blocks and a suitable environment. During replication, the system 

 will occasionally make mistakes. It is a mutable system. Given 

 sufficient time there will eventually occur a combination of mutations 

 of such a nature that the protein coat will become enzymatically active 

 and capable of catalyzing the formation of a nucleotide or amino acid 

 from a slightly simpler precursor. If this particular building block 

 happens to be limiting in replication, the mutant type will obviously 

 have a selective advantage. It can replicate in the absence of an 

 essential building block by making it from a simpler precursor. If 

 two such units with protein coats having different catalytic functions 

 combine to form a two-unit system, they will be able to make two 

 building blocks from simpler compounds and will be able to survive 

 under conditions in which their ancestral forms would fail. In the 

 same way it is not too difficult to imagine systems arising with suc- 

 cessively three, four, five, and more units with every additional unit 

 serving a catalytic function. With each additional unit the total 

 system would become one step less dependent on spontaneously pre- 

 formed precursors. With perhaps ten thousand such units the system 

 might be able to build all its necessary parts from inorganic materials 

 as we know present day green plants do. 



How many units to reach the stage of man ? Perhaps one hundred 

 thousand units carrying out one hundred thousand functions are 

 necessary. However many it is, we know they carry the specifications 

 for the development of a complex nervous system by which we supple- 

 ment blind biological inheritance with cultural inheritance. We 

 reason, we communicate, we accumulate knowledge, and we transmit 

 it to future generations. No other species we know of does this to 

 anything like the same degree. We have even learned about organic 

 evolution and are on the verge of learning how to start the process. 



