ORGANIC EVOLUTION — THE FACTORS 75 



evolution of the horns of deer with the evokition of 

 worker bees. 



Mr. W. I. T. Cunuinfrhame, in his EngUsh translation 

 of Eimer's Organic Evolution, says, " No other mammals 

 have been stated to possess two little symmetrical ex- 

 crescences on the frontal bones as an occasional variation. 

 What caused such excrescences to appear in the ances- 

 tors of horned ruminants ? Butting would produce 

 them, and no other cause can be suggested which 

 would." The last sentence may be amj^lified as follows. 

 " Butting would so irritate or stimulate the periostial 

 cells of the frontal bone as to cause them to deposit 

 more bone, thus giving rise to bony excrescences which, 

 transmitted to descendants, and increased during many 

 generations by more butting, would at last result in 

 horns ; thus, and thus only, can we account for the 

 evolution of horns." Mr. Cunniuffliame notwithstand- 

 ing, it seems to me easy enough to account for the 

 evolution of horns by the theory that inborn variations 

 are alone transmitted, but in doing so we must not 

 seek, as he imagines is necessary, for instances of other 

 mammals which " possess two little symmetrical excres- 

 cences on the frontal bones as an occasional variation." 

 Such excrescences would be rare and abnormal, and evo- 

 lution does not proceed on lines of rare and abnormal 

 variations, which are soon swamped by interbreeding, but 

 on lines of normal variations, as regards which every in- 

 dividual of the species rises above or falls below the spe- 

 cific mean. All ruminants have frontal bones ; when 

 butting became of importance in the unconscious 

 struggle for descendants waged by the hornless ancestors 

 of horned ruminants, it is surely clear that those in- 

 dividuals whose skulls were best adapted to butting, 

 who had varied so that their frontal bones were thick 

 and solid, were, other things equal, at an advantage, and 

 were able to kill or drive away from the females their 



