238 General Discussion 



Blood sugar levels were determined at ten minute intervals for a period 

 of two hours. In all instanees the rate of (lisapi)earanee of glueose from 

 the blood of the older grouj) was substantially less than it was for the 

 young and middle-aged groups. Sinee we also ran standard intravenous 

 glucose tolerance eiuA^es on each subject we were able to show that 

 insulin had a greater effect in the young than in the old. 



Lewis: Dr. Freeman, had any of these schizophrenics received 

 electroconvulsive therapy? 



Freeman: No. 



GENERAL DISCUSSION 



Tunbridge: I think that Prof. Brull and Prof. Verzar suggested almost 

 complementarily that any assessment of ageing should be related to 

 function, and that the functional reserve or the capacity of the indivi- 

 dual under strain was much more likely to give an indication of ageing. 

 In other words, failure of function could be used as a measure of ageing. 

 Prof. Medawar suggested that there might be a heredity factor, and in 

 addition what he referred to as traumatic or environmental factors. Dr. 

 Comfort, would you say something on the role of heredity? We can 

 discuss other aspects afterwards. 



Comfort: I have been waiting in the hope that somebody who knows 

 some genetics would say something about this, but I don't feel that we 

 can just let it pass, and I only hope that you will correct me where I'm 

 wrong. I think we agreed that longevity in laboratory stocks such as 

 we use is hereditary, and longevity in man is "hereditary", but it is 

 rather difficult to specify exactly what we mean by that. We know that 

 some strains we work with live longer than others. In Gruneberg's book 

 on the mouse there are two very nice life tables for inbred lines of mice, 

 showing a very distinct characteristic difference between the two 

 strains. And we know that it is to some extent possible to breed for 

 longevity. Strong conducted some experiments on those lines, but in 

 most cases I think it is fair to say he was selecting against "short-evity", 

 or against specific causes of death. And we know that longevity in man 

 runs in families to some extent also. Now the point I want to make is 

 this. Beeton and Pearson (Biometrika, 1901, 1, 50) a long time ago 

 studied the sib-sib and parent-sib correlations of ages in a long-lived 

 family, and they showed very clearly that there was far greater inter-sib 

 correlation than there was parent-child correlation. In the same series, 

 moreover, the parent-child correlation was, I think, only about one- 

 quarter of that which one would expect in the case of stature. That is, 

 the correlation between tall father and tall son was about four times that 

 between long-lived father and long-lived son. Haldane (Ann. Genet., 

 1949, 14, 288) pointed out that this type of pattern is what you 

 w^ould expect in any case where the heterozygote was inherently fitter 

 than the homozygote, and that does raise some considerable difficulties. 



I don't want to comment on this at great length, but I wonder if I 

 might show you two figures to demonstrate rather briefly the sort of 

 genetical difficulty that arises. Fig. 1 shows the survival curves of 



