134 Discussion 



reasoning, as is shown in Gumbel's treatise (1958). Moreover, life 

 expectations or the median survival times are available for only 

 about six of the 100 or so species that ideally we would like to use in 

 this sort of comparative analysis. Finally, as I pointed out in my 

 paper, maximum lifespan is a better estimator of the intrinsic 

 ageing characteristics of the population than is the median or 

 average survival. However, I do not advocate its use in the analysis 

 of laboratory data, or in any situation where life-tables are available. 



Incidentally, I have been concerned about the problem of what is 

 proper to use as a lifespan for man. Zoo animals are not kept under 

 ideal conditions, as they get little individual attention or medical 

 care. Therefore perhaps some earlier state of human culture would 

 be more comparable. It is interesting that you can get data on the 

 ages of fossil skulls back to the Palaeolithic (Vallois, H. V. (1937). 

 Anthropologic, Paris, 47, 499; Weidenreich, F. (1939). Chin. med. J., 

 55, 34). Peking man, in a sample of only six skulls, yielded one that 

 probably had an age of over 50 years. They lived under far poorer 

 conditions than our zoo animals today. Neolithic man lived to more 

 than 70 years, even according to rather small samples. 



Comfort: I think you have been taking much more plausible 

 maximum ages than Rubner did, Mr. Sacher. Rubner gave the life- 

 span of a dog as nine years and of a cat as eight years, which is 

 quite arbitrary. Cats can quite possibly live for 30 years and the 

 extreme credible record for a dog is between 20 and 25. There are 

 much greater discrepancies between the modal and maximum records 

 for animals, and the acceptable mode and maximum for man. I 

 think most people would agree that 110 to 120 is the extreme limit 

 for which there is any good evidence in man, in spite of the 140- 

 year-old Russians. Most cats die before they are 16, but a few have 

 lived very nearly twice that time. One has also to beware among 

 animals of the possibility of very long-lived genotypes and of the 

 differences between hybrid and inbred strains. 



Sacher: The extreme error in the individual lifespan records is 

 probably a factor of 2 or so, but if the errors are random, their only 

 effect is to weaken the degree of order observed. 



Holt: Have you looked at data for aquatic mammals ? They have 

 some exceptionally large body sizes, without corresponding increases 

 in brain size, and there are many published age determinations for 

 them, but perhaps not maximum lifespans. 



Sacher: When I did this work I did not have enough data on 

 aquatic mammals, but I want to study them in future. 



Maynard Smith: There is a possibility of bias in estimates of this 

 kind since most of the small mammals in your sample are rodents, 



