440 weismann's theory of heredity. 



constituting the condition to the principle of natural selection having 

 been called into play at all. Or in other words, we can not attribute 

 to natural selection the origin of sexual reproduction without involving 

 ourselves in the absurdity of supposing natural selection to have origi- 

 nated the conditions of its own activity.* What the causes may have 

 been which originally led to sexual reproduction is at present a matter 

 that awaits suggestion by way of hypothesis ; and therefore it now 

 only remains to add that the general structure of Professor Weismann's 

 system of hypotheses leads to this curious result, namely, that the 

 otherwise ubiquitous and (as he supposes) exclusive dominion of nat- 

 ural selection stops short at the protozoa, over which it can not exercise 

 any influence at all. For if natural selection depends for its activity 

 on the occurrence of congenital variations, and if congenital variations 

 depend for their occurrence on sexual modes of reproduction, it follows 

 that no organisms which propagate themselves by any other modes can 

 present congenital variations, or thus become subject to the influence 

 of natural selection. And inasmuch as Weismann believes that such 

 is the case with all the protozoa, as well as with all parthenogenetic 

 organisms, he does not hesitate to accept the necessary conclusion that 

 in these cases natural selection is without any jurisdiction. How, then, 

 does he account for individual variations in the protozoa ? And still 

 more, how does he account for the origin of their innumerable species ? 

 He accounts for both these thiugs by the direct action of external con- 



* Since tbia paper was sent to press, Professor Weismann has published in Nature 

 (February 6, 1890 : vol. XLi, pp. 317-323) au elaborate answer to a criticism of 

 his theory by Professor Vines (October 24, 1889: vol. XL, pp. 621-626). In the 

 course of this answer Professor Weismann says that he does attribute the origin of 

 sexual reproduction to natural selection. This directly contradicts what he says in 

 his essays, and for tiie reasons given in the test, appears to me an illogical departure 

 from his previously logical attitude. I herewith append quotations in order to reveal 

 the contradiction : 



*' But when I maintain that the meaning of sexual reproduction is to render possi- 

 ble the transformation of the higher organisms by means of natural selection, such a 

 statement is not equivalent to the assertion that sexual reproduction originally came 

 into existence in order to achieve this end. The eft'octs which are now produced by 

 sexual reproduction did not constitute the causes which led to its first appearance. 

 Sexual reproduction came into existence before it could lead to hereditary individual 

 variability (i. e., to the possibility of natural selection). Its first appearance must, 

 therefore, have had some other cause [than natural selection] ; but the nature of this 

 cause can hardly be determined with any degree of certainty or precision from the 

 facts with which we are at present acquainted." — ("Essay on the Significance of Sex- 

 ual Reproduction in the Theory of Natural Selection : English Translation," pp. 281- 

 282.) 



"I am still of opinion that the origin of sexual reproduction depends on the advan- 

 tage which it aflbrds to the oj)eratiou of natural selection. - - - Sexual reproduction 

 has arisen by and for natural selection as the sole meaus by which individual varia- 

 tions can be united and combined in every possible proportion." — (Nature, Vol. XLi, 

 p. 322.) 



How such opposite statements can be reconciled I do not myself jierceive. — G. J. 

 R., February 17, 1890. 



