EVOLUTION 1097 



(scrutinised, as it were) in relation to what has been estabhshed, 

 those that are congruent being favoured, those that are incongruous 

 being handicapped. 



12. As to the causes of germinal variations, our ignorance remains, 

 as in Darwin's day, "immense"; yet some illuminating suggestions 

 have been made: 



[a) In the early history, maturation divisions, and fertilisation- 



amphimixis of the germ-cells, there are many opportunities 

 for novel permutations and combinations in the chromosomes 

 which carry many (if not all) of the hereditary initiatives 

 (representative factors or genes). In the phenomenon of 

 "crossing over", in which there is exchange of parts between 

 two adjacent chromosomes, there are obvious possibiHties 

 of new arrangements. So in the meiotic division which 

 reduces the number of chromosomes by a half during the 

 maturation of egg-cell and of sperm-cell. So again in the 

 pooling of the paternal and maternal hereditary contribu- 

 tions in the process of fertilisation. 



[b) The germ-cells contain a very intricate equipment of hereditary 



factors, implying an inconceivable chemical complexity; 

 and it may well be that changes are induced (i) by altera- 

 tions in the nutritive stream of the parental body, wherein 

 the germ-cells do not live a charmed life in spite of their 

 segregation, or (2) by modifications induced in the parental 

 body, or (3) by deeply saturating environmental changes, 

 such as change of climate or in irradiation with gamma rays. 



[c) A germ-ceU is an implicit organism; it is richly endowed with 



ancestral contributions; it is alive. So perhaps its varia- 

 bility is in part intrinsic or spontaneous or creative — as 

 primary a quality as irritability. Moreover, the germ-cell 

 is an implicit mind-and-body organism, and it may be that 

 part of the difiiculty of the problem of the origin of the 

 new, is just that it is a psycho-biological phenomenon. 



13. There is little usefulness in speaking of variations as "fortuitous", 

 unless we mean to emphasise the fact that they are usually unpre- 

 dictable; or unless we mean, as Darwin meant, that they are often 

 the outcome of a complex of imperfectly known pre-conditions; 

 or unless we mean that the quantitative amounts of a variation 

 occurring at the same time in a species will show when plotted out 

 the weU-known curve of frequency; or .unless we mean that there 

 may be great diversity in the progeny of the same two parents. In 

 a deeper sense a variation is anything but a chance affair, for it is 

 a re-arrangement of parental or ancestral items, it is the outcome of 

 a pre-established association of genes, unified at the beginning of 

 each new life in the system of the mature germ-cell or of the fertilised 



