426 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



The discovery of how crossing-over happens had long-range conse- 

 quences beyond the previous limits of genetics, for it enabled us to 

 split up the processes of life into two parts. First there are those con- 

 cerned with determining the character of individuals. These are 

 processes of physiology in which the greatest certainty of determina- 

 tion, the strictest predictability in reaction with the environment, a 

 chemical determinism, is achieved ; and second there are the processes 

 of meiosis. These, reinforced by the chances of fertilization which are 

 derived from them, determine the differences in character of indi- 

 viduals. They are the processes of classical genetics in which the 

 greatest uncertainty of determination is organized and achieved. 



This contrast, as I believe, between two kinds of process — the one 

 deterministic, the other spuriously nondeterministic — also provides 

 one of the several ways of splitting genetics into two. It means that 

 instead of speaking of the laws of heredity, as the early Mendelians 

 were fond of doing (making biology echo the physics of the time), we 

 should speak rather of the "paradoxes" of genetics. For heredity is a 

 relation between parent and offspring which is variably compounded 

 of the certain and the uncertain elements, according to how like the 

 parents or grandparents may have been; indeed, accordmg to the 

 effects of their system of breeding. 



THE CONTINUING ISSUE 



I have given an eye-witness account of a battle. I believe it is a 

 battle that we won. The pursuit of the enemy has, to be sure, taken us 

 far away from the original site of the conflict; and it could have 

 taken us much farther with the elasticity of the gene, the organization 

 of the chromosome, or the physiology of the nucleus. But the site of 

 the struggle matters less than its purpose. The enemy, although de- 

 feated and dispersed, has not been destroyed. They will, in my 

 opinion, have to be fought many times again. For mankind, if it hap- 

 pens to take note of the argument, will not willingly admit that its 

 destiny can be revealed by the breeding of flies or the counting of 

 chiasmata. 



REFERENCES 



1. MoKGAN, T. H. Random segregation versus coupling in Mendelian inherit- 



ance. Science, n.s., vol. 34, p. 384, 1911. 

 Morgan, T. H. The theory of the gene. New Haven, 1926. 



2. Janssens, F. A. La th^orie de la chiasmatypie. Cellule, vol. 25, pp. 387-411, 



1909. 



3. MacBride, E. W., et al. The relation of chromosomes to heredity. Nature, 



vol. 98, pp. 424-425, 1915. 

 MacBride, E. W. The present position of the Darwinian theory. Science 

 Progress, vol. 18, pp. 76-96, 1923. 



