322 PLEASANT WA YS IN SCIENCE. 



net for the use of the ideological retiarius as it will be 

 difficult for his Lucretian antagonist to evade, even with the 

 countless turns and doublings of Darwinian evolutions." 



It appears to me that when we observe the analogy be- 

 tween the relationships of individuals, families, and races of 

 man, and the relationships of the various species of animals, 

 the difficulty indicated by Mr. Mivart disappears. Take, for 

 instance, the case of the eight allied families above con- 

 sidered. Suppose, instead of the continual intermarriages 

 before imagined an exceptional order of events, be it re- 

 membered that the more usual order of things prevails, 

 viz., that alliances take place with other families. For sim- 

 plicity, however, imagine that each married pair has two 

 children, male and female, and that each person marries 

 once and only once. Then it will be found that the pair A 

 have ten families of cousins, two first-cousin families, and 

 eight second-cousin families ; these are all the families which 

 share descent from the eight great-grandparents of the pair. 

 (To have third-cousin families we should have to go back to 

 the fourth generation.) Thus there are eleven families in 

 all. Now, in the case first imagined of constant intermarry- 

 ing, there would still have been eleven families, but they 

 would all have descended from eight great-grandparents, 

 and we should then expect to find among the eleven families 

 various combinations, so to speak, of the special charac- 

 teristics of the eight families from which they had descended. 

 On the other hand, eleven families, in no way connected, 

 have descended from eighty-eight great-grandparents, and 

 would present a corresponding variety of characteristics. 

 But in the case actually supposed, in which the eleven 

 families are so related that each one (for what applies to the 

 pair A applies to the others) has two first-cousin families, 

 and eight second-cousin families, it will be found that instead 

 of 88 they have only 56 great-grandparents, or ancestors, in 

 the third generation above them. The two families related 

 as first cousins to the pair A have, like these, eight great- 

 grandparents, four out of these eight for one family, being 



