44 SCIENTIST 



popular books as the recent Calories Don't Count, but 

 they have no standing in the scientific community. 



In the present century, the opposition to mechanical 

 explanations has centered on the problem of growth and 

 differentiation of individual organisms and the evolution 

 of new species. It is admittedly not very easy to explain 

 how a single germ cell determines the development of a 

 complete and highly compficated organism. Early in this cen- 

 tury Hans Driesch further comphcated the problem by show- 

 ing that in certain lower forms (the sea urchin, for example) 

 a single cell of the adult animal is capable of developing 

 a completely new individual. He and some other biologist 

 found this phenomenon impossible to understand on me- 

 chanical grounds and returned in effect to Aristotle's 

 notion of "final causes," which states that in some way 

 the oak is the cause of the growth and development of 

 the acorn. Again, however, this view proved unproduc- 

 tive of new experiments giving clearer insight into the 

 problem. 



Conversely, the plodding and unimaginative mechanist 

 has continued to devise better ways of looking at the indi- 

 vidual cell and of guessing how the blueprint of the 

 developed organism is engraved on its nucleic acids. We 

 are still far from a complete picture of how the process 

 of differentiation and development is timed and guided, 

 but every attempt to explain it in terms of antecedent events 

 has given us new knowledge. The converse attempt to 

 interpret it as the working out of a future purpose has 

 only served to stop people from having useful thoughts 

 on the matter. This is the primary reason that purpose 

 has become a "bad word" among scientists. 



Admittedly the most complex behavior of hving systems 

 at present eludes mechanical analysis. Nevertheless, prog- 

 ress in analyzing such systems without interfering too 



