DARWINISM ATTACKED. 59 



in sexually produced generations ; also, Biometrika, Vol. I, pp. 129- 

 154, 1902, in which Warren shows the variation in parthenogenetic 

 .series of the plant-louse Hyalopterus trirliodus to be as large as 

 the variability exhibited in sexual forms. 



See also Haycraft, J. B., "The Role of Sex," Nat. Science, Vol. 

 VII, pp. 245-250, 342-344, 1895, in which paper is presented an ingen- 

 ious argument to show that sexual reproduction tends not merely not 

 to increase variation but to decrease it : "the convergence to the mean 

 is, then, a result of sexual reproduction : it may be termed the role 

 of sex, and one indeed of no secondary order. The tendency con- 

 stantly to vary is a property inherent in protoplasm, yet often for 

 long periods of time the environment may be the same. In order 

 that a species may continue to live in such a constant environment, 

 the effects of variation must be checked. Sexual multiplication, a 

 conservative function, antagonises the progressive tendency of varia- 

 tion." 



Other naturalists have also held strongly to this view of the role 

 of amphimixis. See Bailey, L. H., "The Plant Individual in the 

 Light of Evolution," address before the Biological Society of Wash- 

 ington. January 12. 1895. Science, N. S., Vol. I, p. 281, 1895, in which 

 paper the author points out the importance of a clear recognition 

 of the tremendous possibilities and actuality of asexual variation 



i 



in plants. 



In a paper by Winslow and Rogers (Science, N. S., Vol. XXL, 

 p. 486. 1905), referring to the classification of bacteria, there is the 

 following statement: "Since the swamping of minor differences by 

 sexual reproduction is absent from bacteria, every inheritable 

 variation is maintained, and instead of true species, we find an infi- 

 nite series of minutely differing but constant races. The only prac- 

 tical method of handling and systematising these, is to establish cer- 

 tain fairly distinct groups and types about which the individual 

 variations may be grouped." 



8 By using a large series of individuals, and carefully tabulating 

 the noted conditions of variation of one or more parts, using, pref- 

 erably, attributes whose variability is capable of being 



Variation ac- mathematically expressed, such as dimensions, num- 

 cording to the law 

 of probabilities. b ers o * spines, or spots, etc., many students have 



shown that these variations seem to occur in most 

 cases according to the law of probabilities, and that a curve plotted 

 so as to express graphically the actual conditions of variation for a 

 given character would be nearly identical with the curve that could 

 be plotted so as to express what variation would exist in the given 

 case if this variation occurred exactly according to the laws of 

 chance. This means that in a thousand individuals collected at 



