FACTS 



229 



Neo-Darwinians, with Weismann, deny the heredity of 

 acquired characters and find no other causes of variation 

 than the mixing of sexes or amphimixis. Consequently they 

 consider successive fecundations as bringing into the living 

 world a series of fortuitous variations, among which natural 

 selection chooses. 



Neo-Lamarckians, with Herbert Spencer, on the contrary, 

 consider that sexual reproduction makes chance variations 

 disappear and, consequently, maintains the average type of 

 the species. Observation seems to verify the theory of 

 Herbert Spencer ; on the other hand, a moment's reflection 

 is enough to understand that, in our way of conceiving 

 sexual phenomena, amphimixis takes an evident part as 

 guardian of the average type of the species. 1 Conse- 

 quently, the role of sexual reproduction in the formation 

 of species appears to us as & simple regulator of adaptive 

 evolution. 



In our next part, however, we shall see that amphimixis 

 may realize, in certain cases, the sudden variations which 

 De Vries has so thoroughly studied under the name of 

 mutations, also called sportive variations. But the part 

 played by mutations in the formation of species does not 

 seem to have the importance now attributed to it by the 

 Neo-Darwinian school. 



Secondary Sexual Characters 



In this matter of sex, it is necessary to point out the notable 

 differences existing between the male and female of certain 

 animals in which sex is separated, like man and other mam- 

 mals. Experiments in castration prove that the genital 

 organ plays a morphogenic part in the production of such 

 differences. But we must also admit that, while the male 



1 See development of this in author's Traite de Biologie. 



