Data for the Problem of Evolution in Man. 



299 



nately our records do not give enough data to determine its form in a 

 reliable manner. 



Fig. 1 seems to indicate a great approach to the Galtonian value 

 towards youth, and we should not be surprised to find the selective 

 death-rate in youth and infancy even more predominant than in old age. 

 This would be the inheritance of the reverse of longevity, of "brachy- 

 bioty." The regression curve for this portion of life cannot be deter- 

 mined from our present statistics, but we hope to return to it in a second 

 study when more data have been collected.* So far as we are able to 

 judge at present the inheritance of the duration of life breaks up into 

 two parts, an inheritance telling its tale in youth and another after 

 middle life. It is the former part which seems to us to have most 

 bearing on the fertility and survival of stocks, most individuals having 

 reproduced themselves by 50 years of age. It is the latter part only, 

 the true inheritance of longevity, to which it would appear that 

 Weismann and Wallace's arguments apply : — f 



"For it is evident than when one or more individuals have pro- 

 vided a sufficient number of successors, they themselves, as consumers 

 of nourishment in a constantly increasing degree, are an injury to 

 those successors. Natural selection therefore weeds them out, and in 

 many cases favours such races as die almost immediately after they 

 have left successors." 



7. We now turn to the third series, giving the correlation between 

 the ages of death of brothers. The data give the following numerical 

 results : — 



M B = 60-971 years. 

 <r B = 16-8354 „ 

 r BB = 0-2602 ±0*0199. 

 E BB = 0-2602 ±0-0216. 



The results here are in good agreement with those for sons in the 

 Landed Gentry, i.e., in the second series. The mean age of one of 

 a pair of brothers is slightly greater and the variability of one who has 

 a brother slightly less than in the case of sons. But this is exactly what 

 we might expect, considering that "brothers" are a selection from 

 "sons," and a brother is likely to have greater vitality than a son. The 

 group sons covers sons of fathers who did not live to have more than one 

 son, and who therefore came of any early dying stock, while brothers 

 denotes at least two sons, and therefore on the average some years 

 more life than is necessary for one son. 



The values of the coefficients of correlation and regression are some 

 13 times their probable errors, and we have a substantial correlation,. 



• 



# This collection has already commenced, and we hope shortly to give more- 

 definite information on this point, 

 f Wallace, loc. cit., svpra. 



z 2 



