EVOLUTION 499 



whence we find - = -2 about. Thus the non -selective 



death-rate is about 20 per cent, the selective death-rate 

 about 80 per cent of the total death-rate. Taking fathers 



20^ 



4S 50 55 60 05 70 75 80 85 80 95 100 105 



Mean Age of First Broftier . 



Fig. 33. 



and sons, who do not live so nearly as brothers under the 

 same environment, a like investigation for the separate 

 series showed a selective death-rate amounting to about 

 65 per cent of the total death-rate. Thus we see that 



