134 THE EVOLUTION OF LIVING BEINGS, 



gotes, and these homozygotes will be decimated in the 

 struggle for Ufe; while if intercrossing continues, selec- 

 tion of the dominant type which seems to be the rule, 

 causes apparent uniformity within suchLinneons.asin 

 the case of the grey rabbits. 



The result is, that from the large number of types 

 arisen from the cross, finally but a few survive. 



Exactly what we see en grand after the appearance 

 of a new Class of organisms. 



Within each Linneon the number of smaller units, 

 of Jordanons, decreases also by selection, — which 

 spells: extermination (of the less fitted types) — 

 until finally but a few or even but one survives. 



If one survives only within a self-fertilising Linneon, 

 its „ variability" is at an end, and therefore it must soo- 

 ner or later die out, and the same must happen if, wi- 

 thin a Linneon, while intercrossing of the different 

 types it contains continues, selection leads to the sur- 

 vival of the recessive tj^e, in stead of to that of the do- 

 minant one, because then its „variabihty" is at an end 

 also, and extinction must foUow. 



That exclusive survival of recessives is one of the 

 chief-reasons of extinction, gains support from the fact 

 that the recent forms of ancient groups are all weak 

 ones, compared to the older ones, and experience goes 

 far to prove that the recessive types are usually the 

 weaker ones. 



Crossing therefore is the cause of the origin of new 

 types, heredity perpetuates them, selection is the cause — 

 not of their origin as was formerly supposed — but of 

 their extinction. 



