440 wki.s.mann'.s theory of heredity. 



oonstitutin<> tlu' condition to tbc i)iincij)le of natural selection having 

 been called into play at all. Or iu otlier ^^•ords, \ve can notattiibnte 

 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.* AVhatthe causes may have 

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

 that awaits suggestion by way of hypothesis; and tlurefore 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 ubi(]uitous and (as he supposes) exclusive dominion of nat- 

 ural selection stO])s short at the protozoa, over which it can not exercise 

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

 on the occun-enco 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 intluence 

 of natural selection. And inasmuch as Weismauu believes that such 

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

 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 si)ecies? 

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



* Since this iiaper was sent to press, Professor Weismann Las published iu Nature 

 (February 6, 1890: vol. XLi, ]}\}. 317-323) an elaborate answer to a criticism of 

 his theory by Professor Vines (October 24, 1869: vol. XL, pp. 621-626). Iu the 

 course of this auswcr Professor AVeismanu says that hQ'does attribute the origin of 

 sexual reproduction to natural selection. This directlj' contradicts what he says iu 

 his essays, and for tlie reasons s^iveu in the text, appears to nic 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 e<|iiivaleut to the assertion that sexual rejtroduction originally came 

 into existence in order to achieve this end. The eil'ects which are now ])roduced bj' 

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

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

 variability (i. c, to the possibility of natural selection). Its lirst appearance mnst, 

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

 cause can hardly be determined with any degree of certainty or i»recision from the 

 facts with which we are at i)resentac<iuainted." — (" Essay on the Siguilicance of Sex- 

 ual Keprodnclion 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 alVords to the operation of uatural. selection. - - - Sexual reproduction 

 has arisen by and for natural selection as the sole nu'ans by which individual varia- 

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

 p. 322.) 



How such opposite statements cau be recouciled 1 do not myscli' perceive. — G. J. 

 K., February 17, 1890. 



