126 THE EVOLUTION OF LIVING BEINGS. 



nize the great importance of hybrids for evolution 

 shows on p. 570, where he states that the number of 

 such hybrids growing wild in Europe, which has beco- 

 me known in the last 40 years preceding the writing of 

 his book, can safely be estimated at 1000 and that the 

 41 Linneons of Coniferae growing in Europe have pro- 

 duced no less than 7 hybrids. 



When we consider further, that not only different 

 Linneons but also different genera intercross f. i. 

 Secale and Triticum, Triticum and Aegilops etc. and 

 that up to the present, we know with certainty of no 

 other way of the formation of new species and new Lin- 

 neons than as a result of crossing, we may, I think, ac- 

 cept safely that the imderlying cause of the diversity of 

 the different t5^es which people the earth, the under- 

 lying cause of evolution, at least as far as diploid orga- 

 nisms is concerned, is hybridization. 



It draws a more complete paralell between the ori- 

 gin of individuals and that of species, on which Darwin 

 insisted already, than his theory did, because according 

 to his conception, species had but one parent, the vary- 

 ing ancestral species, while individuals had two pa- 

 rents ; while according to our view, species as well as in- 

 dividuals have two parents, the first the two parental 

 species from whose cross the new species arose, the lat- 

 ter their father and mother. 



