418 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



At this point Morgan recalled that the previous year the cytologist 

 Janssens [2] at Louvain had made a general proposal about chromo- 

 some behavior. He had noticed that after the pairing of maternal and 

 paternal chromosomes in germ cell formation they fell apart but re- 

 mained touching or attached at various points which he called "chi- 

 asmata." At these points, Janssens suggested, the mating chromosomes 

 might exchange parts by breakage and reunion. Such behavior would 

 give a statistical association or linkage of elements in the same chro- 

 mosome of a kind already to be suspected from Bateson's breeding 

 experiments. Conversely it would lead to the formation of new 

 chromosomes by a recombination of parts. 



Taking Janssens's hint, Morgan and his collaborators proceeded to 

 make crosses between pairs of flies differing in many pairs of respects. 

 They fomid that hundreds of elements could on this assumption be 

 fitted into the four observed pairs of chromosomes of Drosophila. 

 Moreover, if the proportion of regrouping or crossing-over was itself 

 assumed to be related to the distance apart of the elements along each 

 cliromosome, they found that the whole assembly fitted into fixed 

 linear orders. Thus the elements of heredity, or, using Janssens's 

 word, the genes, could be put on a map which, like other maps, showed 

 one how to find one's way about. 



It soon seemed reasonable to advance from these direct inferences 

 to more general principles. Morgan argued that all heredity in all 

 organisms was carried by chromosomes as it was in DrosophUa. 

 Further, all chromosomes were composed of units of crossing-over 

 or mutation which might be known as genes. Hence, he appeared to 

 argue, the genes would add up to give the whole of heredity ; and the 

 differences between them would add up to give the whole of variation 

 and of evolution. 



THE OPPOSITION 



Morgan's "Theory of the Gene" appeared in 1926 ; its reception in 

 England could scarcely have been more unfavorable. Seven men 

 might have been willing to assert their belief in the chromosome 

 theory and give their reasons for it. But against this view there were 

 seven hmidred who held a contrary opinion. The supporters felt 

 liberated by the new theory, its opponents felt confined and oppressed 

 by it. The grounds they gave for their opposition were both general 

 and specific [3]. 



The general objections were that the theory was naive and mechani- 

 ical and yet self-contradictory. For it was both statistical and deter- 

 ministic. It left too much room to chance yet no room to free will. 

 In evolution, moreover, its hard particulate basis shut out the hope of 



