280 



J. Maynard Smith 



population were due to uncontrolled variations in environ- 

 mental conditions. But all the correlations between relatives 

 of like sex were significant and positive, whereas only one of 

 the four correlations between relatives of unlike sex was 

 significantly different from zero. 



The presence of sex-limited genetic variance of longevity is 

 understandable in view of the physiological findings described 

 earlier. Since the causes of ageing in males and ki females are 



Table VII 



CORREL/V-TIONS BETWEEN RELATIVES AMONG THE DESCENDANTS OF 

 FEMALES CAUGHT IN GaLILEE 



at least in part different, it is to be expected that gene dif- 

 ferences should exist with different effects on the longevity of 

 the two sexes. The moral seems to be that the genetics of a 

 character can often be better understood if something is 

 known of its physiology. 



To sum up, the most important conclusion which has 

 emerged from this work seems to be that ageing in Drosophila 

 subobscura is "multiple" in character. The processes re- 

 sponsible for death at 30-5° are reasonably regarded as pro- 

 cesses of "ageing" or "senescence", since they are not 

 reversed or repaired at 20°, and since they take an appreciable 

 time to reach completion. Yet they are not the same as the 

 processes responsible for ageing and death at 20°. Further, 

 the process of egg-laying either accelerates the normal 



